Secondary batteries and electronic devices
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NINGDE AMPEREX TECHNOLOGY LTD
- Filing Date
- 2024-09-30
- Publication Date
- 2026-06-02
Smart Images
Figure CN122139255A_ABST
Abstract
Description
Secondary battery and electronic device TECHNICAL FIELD
[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and an electronic device. BACKGROUND
[0002] With the development of electronic products, the safety performance of batteries is also increasingly required. Smart watches, smart glasses, Bluetooth earphones and mobile phones often fall during use. The electrode assembly in the battery is bonded to the shell of the battery through a glue layer. During the falling process, the electrode assembly and the shell will displace relatively, which is easy to cause the outer electrode tab of the electrode assembly to tear, and there is a safety risk.
[0003] SUMMARY
[0004] The present application aims to provide a secondary battery and an electronic device, and aims to reduce the problem of easy tearing of the electrode tab.
[0005] The embodiments of the present application adopt the following technical solutions:
[0006] In a first aspect, the present application provides a secondary battery, comprising a shell, an electrode assembly and a first tab, the electrode assembly is arranged in the shell, and the electrode assembly comprises a first electrode tab, a separator and a second electrode tab which are stacked and wound. Along the winding direction, the first electrode tab comprises a first single-sided coating section and a first empty foil section connected with each other, the outermost circle electrode tab of the electrode assembly comprises the first empty foil section, and the first tab is connected with the first empty foil section. The first empty foil section comprises a first empty foil surface facing the winding center, and the first empty foil surface is provided with a first insulating layer. The first single-sided coating section comprises a second empty foil surface away from the winding center, and the second empty foil surface is provided with a second insulating layer. The secondary battery further comprises a tailing glue layer bonding the electrode assembly and the shell, and the tailing glue layer comprises a first section, a second section and a third section. Along the winding direction, the first empty foil section comprises a first starting part provided with the first section and a first tailing part provided with the second section, and the first starting part is connected with the first tailing part. The third section is connected between the first section and the second section, and the third section is arranged in the first single-sided coating section. The first single-sided coating section comprises a first position, and along the winding direction, the bonding starting position of the tailing glue layer and the first single-sided coating section is the first position. At the first position, along the thickness direction of the first single-sided coating section, the projection of the tailing glue layer at least partially overlaps with the projection of the first insulating layer and / or the projection of the second insulating layer.
[0007] In the above technical solution, by extending the first insulating layer and / or the second insulating layer and overlapping the tailing glue layer at the first position, the first insulating layer and / or the second insulating layer can disperse part of the shear force received by the first electrode tab, so that the first insulating layer and / or the second insulating layer can resist the tearing of the first electrode tab at the first position, and the anti-collision and anti-impact performance of the secondary battery is improved.
[0008] In some embodiments, the projection of the third segment is within the projection range of the second insulating layer along the thickness direction of the first single-coated segment. By extending the second insulating layer, the impact on the energy density of the secondary battery is small, and the second insulating layer covers part of the second hollow foil segment, which can reduce the corrosion of the electrolyte on the second hollow foil segment.
[0009] In some embodiments, the second insulating layer extends from the second hollow foil surface to the first hollow foil surface, and the projection of the first insulating layer partially overlaps the projection of the second insulating layer along the thickness direction of the first tab. This can make the second insulating layer cover the connection between the first single-coated segment and the first hollow foil segment, reducing the risk of tearing at the connection; and the second insulating layer covers part of the first single-coated segment between the first position and the connection, which can also reduce the risk of tearing of this part of the first single-coated segment.
[0010] In some embodiments, the length of the overlap of the projection of the first insulating layer and the projection of the second insulating layer in the thickness direction of the first tab along the winding direction is L1, and 1mm≤L1≤10mm. This can adapt to the expansion of the tab and the thermal expansion and contraction of the first insulating layer and the second insulating layer, reduce the exposed hollow foil area, and in turn reduce the risk of tearing of the first tab, and can reduce the impact on the energy density of the secondary battery.
[0011] In some embodiments, 3mm≤L1≤5mm, which can further reduce the risk of tearing of the first tab and further reduce the impact on the energy density of the secondary battery.
[0012] In some embodiments, the first single-coated segment includes a first active material layer facing the winding center. The first insulating layer adheres to part of the first active material layer, and the length of the adhesion of the first insulating layer to the first active material layer along the winding direction is L2, and 0.2mm≤L2≤3.6mm. This can reduce the exposed hollow foil area between the first insulating layer and the first active material layer, and in turn reduce the risk of tearing of the first tab and short circuit. Also, it can reduce the edge shedding of the first active material layer, which not only reduces the exposed hollow foil area, but also improves the structural stability of the first active material layer.
[0013] In some embodiments, at the first starting portion, the projection of the first segment overlaps with the projection of the first insulating layer and / or the projection of the second insulating layer at least partially along the thickness direction of the first empty foil segment, so that the first starting portion has a partial first insulating layer and / or a partial second insulating layer, which can resist tearing of the first starting portion and improve the anti-collision and anti-impact performance of the secondary battery. In some other embodiments, at the first ending portion, the projection of the second segment overlaps with the projection of the first insulating layer at least partially along the thickness direction of the first empty foil segment. So that the first ending portion has a partial first insulating layer, which can resist tearing of the first ending portion and further improve the anti-collision and anti-impact performance of the secondary battery.
[0014] In some embodiments, along the thickness direction of the secondary battery, the electrode assembly comprises oppositely arranged first and second flat portions. Along the width direction of the secondary battery, the electrode assembly comprises oppositely arranged first and second curved portions, which are connected between the first and second flat portions. The first position and the first ending portion are both located in the first flat portion or the second flat portion. By arranging the first position in the first flat portion or the second flat portion, stress concentration can be reduced, thereby reducing the risk of tearing of the first electrode tab. Moreover, by locating the first ending portion in the first flat portion or the second flat portion, the processing and the operation of applying the ending adhesive layer can be facilitated, and the regularity and compactness of the electrode assembly can be improved.
[0015] In some embodiments, along the winding direction, the bonding length of the first segment to the first empty foil segment is L3, and 1mm≤L3≤6mm. By reducing the risk of tearing of the first electrode tab, the impact on the energy density can be reduced, thereby reducing the difficulty of the adhesive application process.
[0016] In some embodiments, along the winding direction, the bonding length of the second segment to the first empty foil segment is L4, and 1mm≤L4≤9.5mm. By increasing the bonding length of the second segment to the first ending portion, the stability of the overall structure of the electrode assembly can be improved. Moreover, by reducing the risk of tearing of the first electrode tab, the impact on the energy density can be reduced, thereby reducing the difficulty of the adhesive application process.
[0017] In some embodiments, along the winding direction, the bonding length of the third segment to the first single-sided coated segment is L5, and 1mm≤L5≤10.5mm. By sufficiently dispersing stress, the impact on the energy density can be reduced, thereby reducing the difficulty of the adhesive application process, while reducing the risk of tearing of the first electrode tab.
[0018] In some embodiments, the first insulation layer comprises a first substrate layer and a first adhesive layer, and the first adhesive layer is arranged on a surface of the first substrate layer facing the first tab; and the second insulation layer comprises a second substrate layer and a second adhesive layer, and the second adhesive layer is arranged on a surface of the second substrate layer facing the first tab. The first substrate layer and the second substrate layer each independently comprise at least one of polyethylene terephthalate, polyimide, polypropylene or polyethylene. And / or, the first adhesive layer and the second adhesive layer each independently comprise at least one of acrylic resin, polypropylene, rubber or polyurethane.
[0019] In some embodiments, along the thickness direction of the first tab, the thickness of the first insulation layer is T1, and 10 um≤T1≤31 um, which can effectively isolate the first tab from the second tab, effectively resist tearing of the first tab, and reduce the impact on the surface flatness of the first tab and the loss of energy density.
[0020] In some embodiments, the thickness of the second insulation layer is T2, and 10 um≤T2≤31 um, which can effectively isolate the first tab from the second tab, effectively resist tearing of the first tab, and reduce the impact on the surface flatness of the first tab and the loss of energy density.
[0021] In some embodiments, the secondary battery further comprises a second tab electrically connected to the second tab. Along the width direction of the secondary battery, the distance between the first tab and the second tab is D, and 1.95 mm≤D≤7.6 mm. The space can be fully utilized to improve the energy density of the secondary battery.
[0022] In some embodiments, the width of the secondary battery is W, and 7 mm≤W≤17 mm, which is particularly suitable for products with high space utilization of the secondary battery.
[0023] In a second aspect, the present application further provides an electronic device comprising the secondary battery according to any one of the embodiments of the first aspect.
[0024] Additional layers and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description, drawings, or by implementation of the embodiments of the present application. BRIEF DESCRIPTION OF DRAWINGS
[0025] One or more embodiments are illustrated by way of example in the accompanying drawings, which are not intended to be limiting of the embodiments so as to construct limitations to the embodiments. Elements having the same reference number designates the same elements throughout the drawings, unless otherwise specified. The drawings in the accompanying drawings are not intended to be to scale.
[0026] FIG. 1 is a structural schematic diagram of a secondary battery according to some embodiments of the present application;
[0027] FIG. 2 is a schematic diagram of a winding structure of an electrode assembly according to some embodiments of the present application;
[0028] Fig. 3 is a schematic view of a stack structure of a first tab, a separator film, and a second tab according to some embodiments of the present application;
[0029] Fig. 4 is a schematic view of a partially wound structure of an electrode assembly according to some embodiments of the present application;
[0030] Fig. 5 is a schematic view of a partially wound structure of a first tab according to some embodiments of the present application;
[0031] Fig. 6 is a schematic view of a partially wound structure of a first tab according to some embodiments of the present application;
[0032] Fig. 7 is a schematic view of a partially wound structure of a first tab according to some embodiments of the present application;
[0033] Fig. 8 is a schematic view of a partially wound structure of a first tab according to some embodiments of the present application;
[0034] Fig. 9 is a schematic view of a partially wound structure of a first tab according to some embodiments of the present application;
[0035] Fig. 10 is a schematic view of a partially wound structure of a first tab according to some embodiments of the present application;
[0036] Fig. 11 is a schematic view of a partially wound structure of a first tab according to some embodiments of the present application;
[0037] Fig. 12 is a schematic view of a structure of a first insulating layer and a second insulating layer according to some embodiments of the present application.
[0038] Explanation of Reference Numerals:
[0039] 100, secondary battery;
[0040] 10, case;
[0041] 20, electrode assembly; 20a, first flat portion; 20b, second flat portion; 20c, first curved portion; 20d, second curved portion;
[0042] 21, first tab; 211, first current collector; 212, first active material layer;
[0043] 21a, first empty-foil section; 21a1, first empty-foil surface; 21a2, first insulating layer; 21a21, first base material layer; 21a22, first adhesive layer; 21a3, first start portion; 21a4, first end portion; 21a5, second position; 21a6, third position;
[0044] 21b, first single-sided coated section; 21b1, second empty-foil surface; 21b2, second insulating layer; 21b3, first position; 21b21, second base material layer; 21b22, second adhesive layer;
[0045] 22 second tab; 221 second current collector; 222 second active material layer;
[0046] 23 separator;
[0047] 30 first tab;
[0048] 40 second tab;
[0049] 50 tailing adhesive layer; 51 first section; 52 second section; 53 third section;
[0050] S winding direction; Z first direction; X second direction. DETAILED DESCRIPTION
[0051] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments of the present application.
[0052] In the present application, the phrase “embodiment” means that the specific features, structures or characteristics described in connection with the embodiment can be included in at least one embodiment of the present application. The phrase appears at various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily every embodiment that is independent or alternative to other embodiments.
[0053] In the description of the embodiments of the present application, the technical terms “first”, “second”, etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of “plurality” is two or more, unless otherwise explicitly specified.
[0054] In the description of the embodiments of the present application, the term “and / or” is only a description of the association relationship between the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character “ / ” herein generally represents a “or” relationship between the associated objects.
[0055] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as there is no conflict between them.
[0056] With the development of electronic product technology, electronic products are also increasingly pursuing miniaturization design. For example, for small electronic devices such as smart watches, smart glasses, and Bluetooth headsets, the space utilization rate of secondary batteries is required to be high, and a relatively narrow secondary battery needs to be used. Because the distance between the positive and negative tabs of a relatively narrow secondary battery is relatively close, the positive tab is usually welded to the outermost circle of the positive tab, and the negative tab is usually welded to the outermost circle of the negative tab.
[0057] In order to facilitate the welding of the tabs, the outermost tab usually has a foil-free surface. The electrode assembly needs to be fixed with the shell through the tailing adhesive layer, and the tailing adhesive layer is bonded to the outermost tab of the electrode assembly. The present inventors have found that because the outermost tab of the electrode assembly is provided with a foil-free surface (the outermost circle of the positive tab and the outermost circle of the negative tab need to be provided with a foil-free surface), the strength of the outermost tab is weakened. When the secondary battery is shaken, for example, during impact, impact, etc., the electrode assembly will have a relative motion or a tendency to have a relative motion with the shell, so that the shear force at the junction between the outermost tab bonded to the tailing adhesive layer and the outermost tab not bonded to the tailing adhesive layer is concentrated, which can easily cause the tab to tear.
[0058] To reduce the above problems, in a first aspect, the present application provides a secondary battery 100, please refer to figure 1, the secondary battery 100 includes a shell 10, an electrode assembly 20, a first tab 30 and a second tab 40. The shell 10 can accommodate the electrode assembly 20 and the electrolyte (not shown in the figure), and the electrolyte infiltrates the electrode assembly 20 in the shell 10, so that an electrochemical reaction occurs. One end of the first tab 30 is connected to the electrode assembly 20 in the shell 10, and the other end of the first tab 30 extends out of the shell 10. One end of the second tab 40 is connected to the electrode assembly 20 in the shell 10, and the other end of the second tab 40 extends out of the shell 10. The polarity of the first tab 30 and the second tab 40 is opposite, which is used to lead out the positive and negative electrodes of the secondary battery 100.
[0059] For the above-mentioned electrode assembly 20, please refer to figures 2 and 3, the electrode assembly 20 includes a first tab 21, a second tab 22 and a separator 23. The first tab 21, the separator 23 and the second tab 22 are stacked and wound, for example, stacked along the thickness direction of the first tab 21 and wound along the length direction thereof, to form a wound electrode assembly 20. The separator 23 is arranged between the first tab 21 and the second tab 22, and is used to insulate and separate the first tab 21 and the second tab 22. The polarity of the first tab 21 and the second tab 22 is opposite, the first tab 30 is connected to the first tab 21, and the second tab 40 is connected to the second tab 22, so as to lead out the positive and negative electrodes of the secondary battery 100.
[0060] Referring to Figure 3, the first electrode 21 includes a first current collector 211 and a first active material layer 212. The first current collector 211 serves as the conductive substrate of the first electrode 21 and can be made of a flat aluminum foil. Aluminum foil has high conductivity and low resistance, which can improve the charge / discharge rate of the secondary battery 100. Furthermore, aluminum foil has certain strength and ductility, making it less prone to breakage or deformation during winding or stacking processes, thus ensuring the structural integrity of the first electrode 21. In other embodiments, the first current collector 211 can also be made of titanium foil, nickel foil, or stainless steel foil.
[0061] The first active material layer 212 can be disposed on at least one surface of the first current collector 211 in the thickness direction. The first active material layer 212 includes a positive electrode active material, a conductive agent, and a binder, etc. The above-mentioned material components are mixed, stirred evenly, and coated on the surface of the first current collector 211 to obtain the first active material layer 212. Among them, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium manganese iron phosphate.
[0062] Referring to Figure 3, the second electrode 22 includes a second current collector 221 and a second active material layer 222. The second current collector 221 serves as the conductive substrate of the second electrode 22 and can be made of a flat copper foil. Copper foil has high conductivity and low resistance, which can improve the charge / discharge rate of the secondary battery 100. Furthermore, copper foil has certain strength and ductility, making it less prone to breakage or deformation during winding or stacking processes, thus ensuring the structural integrity of the second electrode 22. In other embodiments, the second current collector 221 can also be made of titanium foil, nickel foil, stainless steel foil, or silver foil.
[0063] The second active material layer 222 can be disposed on at least one surface of the second current collector 221 in the thickness direction. The second active material layer 222 includes a negative electrode active material, a conductive agent, and a binder, etc. These materials are mixed, stirred evenly, and coated on the surface of the second current collector 221 to obtain the second active material layer 222. The negative electrode active material includes one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide, silicon alloy, etc.
[0064] Referring to Figures 3 to 5, the first electrode 21 includes a first single-sided coated section 21b and a first empty foil section 21a. After winding, along the winding direction S, the outermost electrode of the electrode assembly 20 includes the first empty foil section 21a. The first electrode tab 30 is connected to the first empty foil section 21a, and the connection method includes, but is not limited to, welding or conductive adhesive bonding. Optionally, the winding end of the outermost electrode of the electrode assembly 20 is located at the first empty foil section 21a.
[0065] In the embodiments of the present application, the first empty foil section 21a is not provided with an active material layer, and the outermost circle of the electrode assembly 20 is provided with the first empty foil section 21a, which provides a clean, flat and active material-free surface for the connection of the first tab 30, thereby facilitating the connection of the first tab 30 to the first tab 21 and reducing the connection resistance between the first tab 30 and the first tab 21.
[0066] The first empty foil section 21a includes a first empty foil surface 21a1 facing the winding center, and the first empty foil surface 21a1 is provided with a first insulating layer 21a2, which can isolate the first tab 21 from the second tab 22 and reduce the occurrence of short circuit, and the first insulating layer 21a2 can isolate the burrs of the first empty foil surface 21a1, reduce the contact between the burrs and the second tab 22, and further reduce the occurrence of short circuit.
[0067] The first single-sided coating section 21b includes a second empty foil surface 21b1 facing away from the winding center, and the second empty foil surface 21b1 is provided with a second insulating layer 21b2, which can isolate the first single-sided coating section 21b from the second tab 22 and reduce the occurrence of short circuit, and the second insulating layer 21b2 can isolate the burrs of the second empty foil surface 21b1, reduce the contact between the burrs and the second tab 22, and further reduce the occurrence of short circuit.
[0068] The first single-sided coating section 21b also includes a first active material layer 212 facing the winding center, please refer to FIG. 4 and FIG. 5, because the first single-sided coating section 21b has a corresponding second active material layer 222 only on one side facing the winding center, therefore the first active material layer 212 can be provided on the side facing the winding center, which can facilitate the electrochemical reaction with the corresponding second active material layer 222. And the side away from the winding center has no second active material layer 222, and the second empty foil surface 21b1 can be directly provided, thereby saving space and improving the energy density of the secondary battery 100.
[0069] During the process of being subjected to impact or shock, the electrode assembly 20 will move within the shell 10, which is easy to cause the deformation and misplacement of the positive and negative tabs, and may cause the positive and negative tabs to contact and short circuit, especially for the relatively narrow secondary battery 100, because the distance between the positive and negative tabs is small, the risk of short circuit caused by the contact between the positive and negative tabs is high. In order to reduce this problem, the secondary battery 100 of the embodiments of the present application also includes an end adhesive layer 50, which bonds the electrode assembly 20 and the shell 10, thereby reducing the relative movement between the electrode assembly 20 and the shell 10, and further reducing the short circuit caused by the deformation or misplacement of the positive and negative tabs.
[0070] Referring to FIG. 5, the tailing adhesive layer 50 includes a first section 51, a second section 52, and a third section 53, and the third section 53 is connected between the first section 51 and the second section 52. In the winding direction S, the first empty foil section 21a includes a first starting portion 21a3 and a first tailing portion 21a4, the first section 51 is arranged at the first starting portion 21a3, and the second section 52 is arranged at the first tailing portion 21a4. There is a partial first single-coated section 21b between the first tailing portion 21a4 and the first starting portion 21a3, and the third section 53 is bonded to the partial first single-coated section 21b.
[0071] The tailing adhesive layer 50 can bond the first starting portion 21a3, the first tailing portion 21a4, and the partial first single-coated section 21b, so as to improve the compactness of the electrode assembly 20 and the energy density of the secondary battery 100. In addition, when the secondary battery 100 is subjected to a collision or an impact, the arrangement of the tailing adhesive layer 50 can reduce the looseness of the electrode tab and improve the structural stability of the electrode assembly 20. In addition, the tailing adhesive layer 50 can also reduce the contact between the first tailing portion 21a4 and the shell 10, and can isolate part of the electrolyte, thereby reducing the corrosion of the first tailing portion 21a4.
[0072] It should be noted that, for the definition of the first starting portion 21a3 and the first tailing portion 21a4, in the embodiments of the present application, the first section 51 arranged at the first starting portion 21a3 of the first empty foil section 21a is regarded as the first starting portion 21a3, and the second section 52 arranged at the first tailing portion 21a4 of the first empty foil section 21a is regarded as the first tailing portion 21a4.
[0073] Referring to FIG. 5, the first single-coated section 21b includes a first position 21b3, and the bonding starting position of the tailing adhesive layer 50 and the first single-coated section 21b in the winding direction S is the first position 21b3. The present inventor has found that the tailing adhesive layer 50 has a certain elasticity and flexibility, while the first single-coated section 21b has a larger hardness and smaller elasticity, and the shear force is easily concentrated at the first position 21b3, especially when the secondary battery 100 is subjected to a collision or an impact, because of the relative movement or the trend of relative movement between the electrode assembly 20 and the shell 10, the shear force at the first position 21b3 is increased, which easily causes the first single-coated section 21b to be torn at the first position 21b3.
[0074] The tearing of the first electrode tab 21 can cause the active material layer to fall off, resulting in a loss of energy density of the secondary battery 100 and an increase in internal resistance, which affects the charge-discharge rate of the secondary battery 100. At the same time, the tearing of the electrode tab can pierce the separator 23, causing the positive and negative electrodes to directly contact and cause internal short circuit, which can cause thermal runaway, resulting in safety risks such as fire and explosion of the secondary battery 100.
[0075] To reduce the tearing problem of the first pole piece 21, in the embodiments of the present application, at the first position 21b3, the projection of the tailing adhesive layer 50 along the thickness direction of the first single-sided coating section 21b at least partially overlaps the projection of the first insulating layer 21a2 and / or the projection of the second insulating layer 21b2. By extending the first insulating layer 21a2 and / or the second insulating layer 21b2 and overlapping the tailing adhesive layer 50 at the first position 21b3, the first insulating layer 21a2 and / or the second insulating layer 21b2 can disperse part of the shearing force received by the first pole piece 21, so that the first insulating layer 21a2 and / or the second insulating layer 21b2 can resist the tearing of the first pole piece 21 at the first position 21b3, and improve the anti-collision and anti-impact performance of the secondary battery 100.
[0076] In some embodiments, as shown in FIG. 5, the second insulating layer 21b2 can be extended and beyond the first position 21b3; or as shown in FIG. 6, the first insulating layer 21a2 can be extended and beyond the first position 21b3; or as shown in FIG. 7, at the first position 21b3, the first insulating layer 21a2 and the second insulating layer 21b2 overlap along the thickness direction of the first pole piece 21.
[0077] In some embodiments, as shown in FIG. 5, the projection of the third section 53 along the thickness direction of the first single-sided coating section 21b is located within the projection range of the second insulating layer 21b2. The side of the first single-sided coating section 21b facing the winding center includes the first active material layer 212, and extending the first insulating layer 21a2 will cover part of the first active material layer 212, so that this part of the active material layer cannot participate in the electrochemical reaction, which will cause the energy density loss of the secondary battery 100. In the embodiments of the present application, it is preferred to extend the second insulating layer 21a2, which has less impact on the energy density of the secondary battery 100, and the second insulating layer 21b2 covers part of the second empty foil section 21b1, which can reduce the corrosion of the electrolyte to the second empty foil section.
[0078] The present inventors have found that there is a section difference at the connection between the first single-sided coating section 21b and the first empty foil section 21a, and the connection is also prone to shearing force concentration, and the first pole piece 20 has a high risk of tearing. To reduce this problem, in the embodiments of the present application, as shown in FIG. 5, the second insulating layer 21b2 is extended from the second empty foil surface 21b1 to the first empty foil surface 21a1, so that the second insulating layer 21b2 covers the connection between the first single-sided coating section 21b and the first empty foil section 21a, reducing the risk of tearing at the connection; and the second insulating layer 21b2 covers part of the first single-sided coating section 21b between the first position 21b3 and the connection, which also reduces the risk of tearing of this part of the first single-sided coating section 21b.
[0079] Referring to FIG. 5, at the first starting portion 21a3, the projection of the first segment 51 overlaps at least partially with the projection of the first insulating layer 21a2 and / or the projection of the second insulating layer 21b2 along the thickness direction of the first empty foil segment 21a, so that the first starting portion 21a3 is bonded with part of the first insulating layer 21a2 and / or part of the second insulating layer 21b2, which can resist tearing of the first starting portion 21a3 and improve the anti-collision and anti-impact performance of the secondary battery 100.
[0080] Referring to FIG. 6, the first empty foil segment 21a includes a second position 21a5, which is the junction of the first empty foil segment 21a bonded with the tailing adhesive layer 50 and the first empty foil segment 21a not bonded with the tailing adhesive layer 50. The second position 21a5 also has shear force concentration, which is prone to tearing of the first electrode tab 21. In the embodiments of the present application, referring to FIG. 5, the second insulating layer 21b2 extends from the first single-sided coating segment 21b to the first empty foil segment 21a along the winding direction S, and the second insulating layer 21b2 exceeds the first segment 51 of the tailing adhesive layer 50, so that the first starting portion 21a3 is covered by the second insulating layer 21b2, which can sufficiently disperse stress and reduce tearing of the first electrode tab at the second position.
[0081] In other embodiments, referring to FIG. 6, at the first tailing portion 21a4, the projection of the second segment 52 overlaps at least partially with the projection of the first insulating layer 21a2 along the thickness direction of the first empty foil segment 21a, so that the first tailing portion 21a4 is bonded with part of the first insulating layer 21a2, which can resist tearing of the first tailing portion 21a4 and further improve the anti-collision and anti-impact performance of the secondary battery 100.
[0082] The first empty foil segment also includes a third position 21a6, which is also the junction of the first empty foil segment 21a bonded with the tailing adhesive layer 50 and the first empty foil segment 21a not bonded with the tailing adhesive layer 50. The third position 21a6 also has shear force concentration, which is prone to tearing of the first electrode tab 21. The first insulating layer 21a2 can be extended along the winding direction S and exceed the third position 21a6, which can disperse shear force at the third position 21a6 and reduce tearing of the first electrode tab 21 at the third position 21a6.
[0083] In some embodiments, referring to FIG. 8, the second insulating layer 21b2 extends from the second empty foil surface 21b1 to the first empty foil surface 21a1, and the projection of the first insulating layer 21a2 partially overlaps with the projection of the second insulating layer 21b2 along the thickness direction of the first electrode tab 21, so that the first starting portion 21a3 bonded with the first segment 51 and part of the first single-sided coating segment 21b bonded with the third segment 53 are covered by the first insulating layer 21a2 and / or the second insulating layer 21b2, which can reduce tearing of the first starting portion 21a3.
[0084] The inventors of the present application have found that, along the winding direction S, if the length of the overlap of the projection of the first insulating layer 21a2 and the projection of the second insulating layer 21b2 in the thickness direction of the first pole piece 21 is too small, the first pole piece 21 may have poor tear resistance. For example, during long-term charge and discharge cycles, the pole piece may expand, and the thermal expansion and contraction of the first insulating layer 21a2 and the second insulating layer 21b2 may cause the first insulating layer 21a2 and the second insulating layer 21b2 to be misaligned in the thickness direction of the first pole piece 21, causing the first pole piece 21 to expose a portion of the empty foil area. The empty foil area itself has weak strength and is prone to shear force concentration, which may also cause the pole piece to tear. If the length is too large, the energy density of the secondary battery 100 may be lost, and the first insulating layer 21a2 may cover the first active material layer 212, resulting in waste and further loss of energy density.
[0085] In embodiments of the present application, referring to FIG. 8, along the winding direction S, the length of the overlap of the projection of the first insulating layer 21a2 and the projection of the second insulating layer 21b2 in the thickness direction of the first pole piece 21 is L1, and 1 mm≤L1≤10 mm. This length can accommodate the expansion of the pole piece and the thermal expansion and contraction of the first insulating layer 21a2 and the second insulating layer 21b2, reduce the exposed empty foil area, and further reduce the risk of tearing of the first pole piece 21. Moreover, this length can reduce the impact on the energy density of the secondary battery 100.
[0086] In some embodiments, 3 mm≤L1≤5 mm, which can further reduce the risk of tearing of the first pole piece 21 and further reduce the impact on the energy density of the secondary battery 100.
[0087] In some embodiments, the first insulating layer 21a2 can also bond a portion of the first active material layer 212. If the bonding length of the first insulating layer 21a2 and the first active material layer 212 is too small, a portion of the empty foil area between the first insulating layer 21a2 and the first active material layer 212 may be exposed, which may cause the empty foil area to contact the second pole piece 22 and short circuit. If the second insulating layer 21b2 does not extend to the junction of the first single-coated section 21b and the first empty foil section 21a, the exposed portion of the empty foil area will have no corresponding insulating layer to resist tearing, and the first pole piece 21 may also be at risk of tearing. If the bonding length is too large, the portion of the first active material layer 212 that is bonded may be difficult to participate in or even unable to participate in electrochemical reactions, resulting in a loss of energy density of the secondary battery 100.
[0088] To reduce the above problems, in embodiments of the present application, referring to FIG. 9, the first insulating layer 21a2 extends from the first empty foil surface 21a1 to the first active material layer 212, and the bonding length of the first insulating layer 21a2 and the first active material layer 212 along the winding direction S is L2, 0.2mm≤L2≤3.6mm. Limiting L2≥0.2mm can reduce the exposed empty foil area between the first insulating layer 21a2 and the first active material layer 212, thereby reducing the risk of tearing of the first tab 21 and reducing the risk of short circuit. Moreover, it can reduce the edge falling of the first active material layer 212, not only can reduce the exposure of the empty foil area, but also can improve the structural stability of the first active material layer 212. Limiting L2≤3.6mm can reduce the impact on energy density.
[0089] Optionally, the first tab 21 is a positive electrode tab, and the second tab 22 is a negative electrode tab. In embodiments of the present application, limiting 0.2mm≤L2≤3.6mm, the first insulating layer 21a2 covers part of the first active material layer 212, which can facilitate the second tab 22 to have sufficient excess to embed the lithium ion discharged from the first tab 21, thereby effectively reducing the occurrence of lithium precipitation.
[0090] For the thickness of the first insulating layer 21a2, if the thickness is too large, it will cause the flatness of the surface of the first tab 21 to decrease, and also will cause the loss of energy density. If the thickness is too small, it may lead to insufficient insulation and difficulty in resisting tearing of the first tab 21. In embodiments of the present application, along the thickness direction of the first tab 21, the thickness of the first insulating layer 21a2 is T1, 10um≤T1≤31um, which can effectively isolate the first tab 21 and the second tab 22, and can effectively resist tearing of the first tab 21 and the impact on the flatness of the surface of the first tab 21, thereby reducing the loss of energy density.
[0091] Based on the same inventive concept, along the thickness direction of the first tab 21, the thickness of the second insulating layer 21b2 is T2, 10um≤T2≤31um, which can effectively isolate the first tab 21 and the second tab 22, and can effectively resist tearing of the first tab 21 and the impact on the flatness of the surface of the first tab 21, thereby reducing the loss of energy density.
[0092] In some embodiments, referring to FIG. 10, along the thickness direction (the first direction Z) of the secondary battery 100, the electrode assembly 20 includes oppositely arranged first and second flat portions 20a and 20b. Along the width direction (the second direction X) of the secondary battery 100, the electrode assembly 20 includes oppositely arranged first and second curved portions 20c and 20d, which are connected between the first and second flat portions 20a and 20b. The first position 21b3 and the first end portion 21a4 are both located in the first flat portion 20a or the second flat portion 20b.
[0093] During the use of the secondary battery 100, the bending part bears a large stress change, and the first position 21b3 located at the bending part can increase the risk of tearing of the first electrode tab 21. By arranging the first position 21b3 at the first flat part 20a or the second flat part 20b, the stress concentration can be reduced, and thus the risk of tearing of the first electrode tab 21 can be reduced. In addition, the first end part 21a4 is located at the first flat part 20a or the second flat part 20b, which not only facilitates the processing and the operation of pasting the end adhesive layer 50, but also improves the regularity and compactness of the electrode assembly 20.
[0094] For the bonding length of the end adhesive layer 50 and each part of the first electrode tab 21. If the bonding length is too small, stress concentration is easy to occur, and the first electrode tab 21 is easy to tear when the secondary battery 100 is subjected to collision or impact. If the bonding length is too large, the end adhesive layer 50 occupies too much space, which not only causes loss of energy density, but also increases the difficulty of the adhesive process.
[0095] In the embodiments of the present application, please refer to FIG. 11. Along the winding direction S, the bonding length of the first section 51 and the first empty foil section 21a is L3, and 1mm≤L3≤6mm. The bonding length can reduce the risk of tearing of the first electrode tab 21, reduce the impact on the energy density, and reduce the difficulty of the adhesive process.
[0096] Along the winding direction S, the bonding length of the second section 52 and the first empty foil section 21a is L4, and 1mm≤L4≤9.5mm. The second section 52 is bonded to the first end part 21a4, and the first end part 21a4 is the winding end section of the electrode assembly 20, which is more prone to loosen. Therefore, the bonding length of the second section 52 and the first end part 21a4 can be increased, and the stability of the overall structure of the electrode assembly 20 can be improved. In addition, by limiting 1mm≤L4≤9.5mm, the risk of tearing of the first electrode tab 21 can be reduced, the impact on the energy density can be reduced, and the difficulty of the adhesive process can be reduced.
[0097] Along the winding direction S, the bonding length of the third section 53 and the first single-sided coating section 21b is L5, and 1mm≤L5≤10.5mm. The third section 53 is the part of the first electrode tab 21 that is prone to tearing. By limiting 1mm≤L5≤10.5mm, the stress can be fully dispersed, the risk of tearing of the first electrode tab 21 can be reduced, the impact on the energy density can be reduced, and the difficulty of the adhesive process can be reduced.
[0098] In some embodiments, please refer to FIG. 12. The first insulating layer 21a2 includes a first substrate layer 21a21 and a first bonding layer 21a22, and the first bonding layer 21a22 is arranged on the surface of the first substrate layer 21a21 facing the first electrode tab 21.
[0099] The first substrate layer 21a21 includes at least one of polyethylene terephthalate, polyimide, polypropylene or polyethylene, each of which has good insulation performance and high mechanical strength, can provide support for the first adhesive layer 21a22, reduce the deformation of the entire first insulation layer 21a2, and thus effectively resist tearing of the first pole piece 21.
[0100] The first adhesive layer 21a22 includes at least one of acrylic resin, polypropylene, rubber or polyurethane, each of which has good insulation performance and better adhesion, can form a firm bond with the first substrate layer 21a21 and the first pole piece 21, and has better corrosion resistance, which can reduce corrosion by electrolyte and improve the service life of the entire first insulation layer 21a2.
[0101] Based on the same inventive concept, the second insulation layer 21b2 includes a second substrate layer 21b21 and a second adhesive layer 21b22, the second adhesive layer 21b22 being arranged on the surface of the second substrate layer 21b21 facing the first pole piece 21. The second substrate layer 21b21 includes at least one of polyethylene terephthalate, polyimide, polypropylene or polyethylene. The second adhesive layer 21b22 includes at least one of acrylic resin, polypropylene, rubber or polyurethane.
[0102] In the embodiments of the present application, the first tab 30 is connected to the outermost circle of the first pole piece 21, and the second tab 40 is connected to the outermost circle of the second pole piece 22, which can make the internal structure of the secondary battery 100 more compact. For example, referring to FIGS. 1, 2 and 4, the distance between the first tab 30 and the second tab 40 along the width direction (second direction X) of the secondary battery 100 is D, and 1.95mm≤D≤7.6mm, which can make full use of the space and improve the energy density of the secondary battery 100. Moreover, connecting the tabs to the outermost circle can simplify the process and improve the production efficiency. It is particularly suitable for relatively narrow secondary batteries 100, for example, the width W of the secondary battery 100 is 7mm≤W≤17mm, and is particularly suitable for products with high space utilization of the secondary battery 100.
[0103] In a second aspect, the present application also provides an electronic device comprising the secondary battery 100 according to any one of the embodiments of the first aspect described above. The electronic device of the embodiments of the present application is not particularly limited and can be any electronic device known in the prior art. For example, the electronic device includes but is not limited to Bluetooth earphones, mobile phones, tablets, notebook computers, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Among them, the electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric plane toys, etc., and the spacecraft can include airplanes, rockets, space shuttles and spaceships, etc.
[0104] Embodiment 1
[0105] Preparation of the positive electrode sheet
[0106] The positive electrode active material lithium cobaltate (LiCoO2), the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride were mixed in a mass ratio of 97.9:0.9:1.2, N-methyl pyrrolidone (NMP) was added as a solvent, and a slurry with a solid content of 75 wt% was prepared. After uniform stirring in a vacuum, a positive electrode slurry was obtained.
[0107] An aluminum foil with a thickness of 8 μm was selected as the positive electrode current collector. The positive electrode slurry was uniformly coated on one surface of the positive electrode current collector aluminum foil, and the coating weight was 0.135 mg / mm 2 , and a first empty foil area was reserved on the positive electrode current collector. After drying at 110 °C, a positive electrode sheet with a single positive electrode active material layer was obtained. Subsequently, the above steps were repeated on the other surface of the aluminum foil, and a second empty foil area was reserved on the surface, the first empty foil area and the second empty foil area were arranged opposite to each other in the thickness direction of the positive electrode current collector, thereby forming a first empty foil section. The length of the first empty foil area and the second empty foil area in the length direction of the positive electrode current collector was different, thereby forming a first single empty foil section with the positive electrode active material layer on one side and the other empty foil area. The specification of the positive electrode sheet was 40.7 mm x 403.5 mm, and the thickness of the single-layer positive electrode active material layer was 39.1 μm. An aluminum sheet with a width of 2 mm was selected as the positive electrode sheet, and the positive electrode tab was welded to the first empty foil section.
[0108] Preparation of the negative electrode sheet
[0109] The artificial graphite, the binder styrene-butadiene rubber, and the conductive agent acetylene black were mixed in a mass ratio of 97.7:0.8:1.5, deionized water was added as a solvent, and a slurry with a solid content of 50 wt% was prepared. After uniform stirring in a vacuum, a negative electrode slurry was obtained.
[0110] A copper foil with a thickness of 6 μm was selected as the negative electrode current collector. The negative electrode slurry was uniformly coated on one surface of the negative electrode current collector copper foil, and the coating weight was 0.075 mg / mm 2 , and a third empty foil area was reserved on the copper foil. After drying at 120 °C, a single negative electrode sheet was obtained. After the above steps were completed, the single coating of the negative electrode sheet was completed. Subsequently, the above steps were repeated on the other surface of the negative electrode sheet, and a fourth empty foil area was reserved on the surface, the third empty foil area and the fourth empty foil area were arranged opposite to each other in the thickness direction of the negative electrode current collector, thereby forming a second empty foil section of the negative electrode sheet. A nickel sheet with a width of 2 mm was selected as the negative electrode tab, and the negative electrode tab was welded to the second empty foil section. The specification of the negative electrode sheet was 42.2 mm x 391.6 mm, and the thickness of the single-layer negative electrode active material layer was 38.6 μm.
[0111] <Preparation of the separator>
[0112] A porous polyethylene (PE) film with a thickness of 5 μm was used as the separator.
[0113] <Preparation of the electrolyte>
[0114] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate were mixed in a mass ratio of 30:50:20 to obtain an organic solvent, and then lithium salt lithium hexafluorophosphate was dissolved and uniformly mixed in the organic solvent to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.
[0115] <Preparation of the first and second insulation layers>
[0116] Polyethylene terephthalate was selected as the first base material layer, and acrylic resin was selected as the first adhesive layer. The first adhesive layer was compounded on the first base material layer to form a first insulation layer with a thickness of 20 μm. The first insulation layer was adhered to one surface of the first empty foil section. In a similar manner, a second insulation layer with a thickness of 20 μm was prepared, and the second insulation layer was adhered to the empty foil surface of the first single-sided coated section.
[0117] <Preparation of the finishing adhesive layer>
[0118] Styrene-isoprene-styrene block copolymer was heated to 150°C to form a hot melt, which was then coated on one surface of a polyethylene terephthalate film with a thickness of 8 μm, and then dried at 120°C to form a first adhesive layer with a thickness of 8 μm. Polyacrylic acid (PAA) was coated on the other surface of the polyethylene terephthalate film and dried at 80°C to form a second adhesive layer with a thickness of 4 μm, thereby obtaining a finishing adhesive layer containing the second adhesive layer, the polyethylene terephthalate film and the second adhesive layer, which were sequentially stacked.
[0119] <Preparation of the lithium ion battery>
[0120] The separator, the positive electrode sheet, the separator, and the negative electrode sheet prepared above were sequentially stacked and wound to obtain an electrode assembly. After winding, the first insulation layer faced the winding center, the second insulation layer faced away from the winding center, and the first empty foil section formed the outermost part of the electrode assembly. A part of the finishing adhesive layer adhered to the finishing part of the first empty foil section, and another part adhered to the starting part of the first empty foil section, and the finishing adhesive layer adhered to the first single-sided coated section. Among them, along the winding direction, the starting position of the finishing adhesive layer adhered to the first single-sided coated section was the first position, and at the first position, the second insulation layer overlapped with the finishing adhesive layer along the thickness direction of the positive electrode sheet.
[0121] The punched aluminum plastic film is placed in the assembly clamp with the pit facing down, and the electrode assembly is placed in the pit and pressed tightly. Then the other pit of the punched aluminum plastic film is covered on the electrode assembly with the pit facing up, and the two edges of the aluminum plastic film are heat sealed by heat pressing. One of the heat sealed edges is the side where the negative and positive tabs protrude out of the shell. Then electrolyte is injected through the unsealed edge, and the lithium ion battery is obtained after vacuum packaging, standing, heat pressing, and shaping.
[0122] The relevant parameters in examples 2 to 14 and comparative example 1 are shown in Table 1, which are different from those in example 1. In examples 3 to 14, the first insulating layer and the second insulating layer overlap in the thickness direction of the first tab, and the overlapping length L1 in the winding direction is shown in Table 1.
[0123] Drop test method: The lithium ion battery is placed in a 25℃ environment for 30 minutes, and then charged in the following steps: constant current charging at 0.5C to 4.4V, and constant voltage charging to 0.02C. After standing for 60 minutes, the voltage of the lithium ion battery is tested. The lithium ion battery is loaded into a clamp and dropped from a height of 1.5m using a drop device in the following order: back- front-left side-right side-bottom-head-right upper corner-left upper corner-left lower corner-right lower corner, and repeated for 1 round. After the drop test, the lithium ion battery is allowed to stand at room temperature for 24 hours, and the voltage of the lithium ion battery is measured and recorded. The appearance of the lithium ion battery is checked before and after the test and photographed. The drop test passes the following criteria: the lithium ion battery must be able to work, the voltage drop must be less than 30mv, and the tab must not be torn when the lithium ion battery is disassembled. The number of lithium ion batteries that pass the test is X, and the test pass rate is X / 20.
[0124] Table 1
[0125] According to Table 1 above, in combination with examples 1 to 14 and comparative example 1, when the end adhesive layer overlaps with at least one of the first insulating layer and the second insulating layer, the risk of tab tearing can be effectively reduced. This is because the first insulating layer and / or the second insulating layer can disperse part of the shear force, so that the first insulating layer and / or the second insulating layer can resist tearing of the first tab at the first position, thereby improving the anti-collision and anti-impact performance of the secondary battery.
[0126] In examples 3 to 14, the risk of drop failure is lower than that in examples 1 and 2. In examples 3 to 14, the first insulating layer and the second insulating layer overlap in the thickness direction of the first tab, which can fully cover the bonding area of the end adhesive layer and the first tab, reduce the concentration of shear force, and thereby reduce the tearing of the first tab.
[0127] In Embodiments 4-14, the drop test pass rate is higher than that of Embodiment 3. In Embodiments 4-14, the first insulating layer and the second insulating layer have sufficient overlap length to adapt to the expansion of the pole piece and the thermal expansion and contraction of the first insulating layer and the second insulating layer, reducing the exposed empty foil area and thereby reducing the risk of tearing of the first pole piece. The drop test pass rate of Embodiment 14 is close to that of Embodiments 6-10, but in Embodiment 14, the overlap length is too large, which can cause energy density loss. Therefore, in the embodiments of the present application, 1mm≤L1≤10mm can be selected.
[0128] In Embodiments 6-8, the drop test pass rate is close to that of Embodiments 9-14, but in Embodiments 5-8, the overlap length of the first insulating layer and the second insulating layer is smaller, and the impact on the energy density is smaller. Therefore, in the embodiments of the present application, 3mm≤L1≤5mm is preferred, which can further reduce the impact on the energy density while reducing the risk of tearing of the first pole piece.
[0129] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; under the idea of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other changes of different aspects of the present application as described above, which are not provided in detail for simplicity; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.
Claims
1. A secondary battery, comprising a case, an electrode assembly disposed in the case, and a first tab, the electrode assembly comprising a first electrode sheet, a separator, and a second electrode sheet stacked and wound, the first electrode sheet comprising a first single-coated section and a first empty-foil section connected in series along a winding direction, an outermost coil of the electrode assembly comprising the first empty-foil section, the first tab being connected to the first empty-foil section; The first empty foil section includes a first empty foil surface facing a winding center, and the first empty foil surface is provided with a first insulation layer; the first single-sided coating section includes a second empty foil surface facing away from the winding center, and the second empty foil surface is provided with a second insulation layer; the secondary battery further includes a finishing adhesive layer, and the finishing adhesive layer bonds the electrode assembly and the shell; characterized in that, the end-tail adhesive layer comprising a first section, a second section, and a third section; along the winding direction, the first empty-foil section comprising a first start portion and a first end portion, the first start portion being provided with the first section, the first end portion being provided with the second section; the third section being connected between the first section and the second section, and the third section being disposed on the first single-coated section; the first single-coated section comprising a first position, along the winding direction, a bonding start position of the end-tail adhesive layer and the first single-coated section being the first position; at the first position, along a thickness direction of the first single-coated section, a projection of the end-tail adhesive layer at least partially overlaps with a projection of the first insulating layer and / or a projection of the second insulating layer.
2. The secondary battery according to claim 1, characterized by along the thickness direction of the first single-coated section, a projection of the third section is located within a projection range of the second insulating layer.
3. The secondary battery according to claim 1 or 2, characterized by the second insulating layer extending from the second empty-foil surface to the first empty-foil surface, along a thickness direction of the first electrode sheet, a projection of the first insulating layer partially overlaps with a projection of the second insulating layer.
4. The secondary battery according to claim 3, characterized by along the winding direction, a length of overlap of the projection of the first insulating layer and the projection of the second insulating layer in the thickness direction of the first electrode sheet is L1, 1mm≤L1≤10mm.
5. The secondary battery according to claim 4, characterized by 3mm≤L1≤5mm.
6. The secondary battery according to any one of claims 1 to 5, characterized by the first single-coated section comprising a first active material layer facing the winding center; the first insulating layer bonding the first active material layer, along the winding direction, a bonding length of the first insulating layer and the first active material layer is L2, 0.2mm≤L2≤3.6mm.
7. The secondary battery according to any one of claims 1 to 6, characterized by at the first start portion, along a thickness direction of the first empty-foil section, a projection of the first section at least partially overlaps with a projection of the first insulating layer and / or a projection of the second insulating layer; and / or, at the first end portion, along a thickness direction of the first empty-foil section, a projection of the second section at least partially overlaps with a projection of the first insulating layer.
8. The secondary battery according to any one of claims 1 to 7, characterized by, along a thickness direction of the secondary battery, the electrode assembly comprising a first flat portion and a second flat portion disposed oppositely; along a width direction of the secondary battery, the electrode assembly comprising a first curved portion and a second curved portion disposed oppositely, the first curved portion and the second curved portion being connected between the first flat portion and the second flat portion; the first position and the first end portion are both located in the first flat portion or the second flat portion.
9. The secondary battery according to any one of claims 1 to 8, characterized by, along the winding direction: The bonding length of the first segment to the first empty foil segment is L3, 1mm≤L3≤6mm; and / or, the bonding length of the second segment to the first empty foil segment is L4, 1mm≤L4≤9.5mm; and / or, the bonding length of the third segment to the first single-coated segment is L5, 1mm≤L5≤10.5mm.
10. The secondary battery according to any one of claims 1 to 9, characterized by The first insulating layer comprises a first base material layer and a first bonding layer, the first bonding layer being arranged on the surface of the first base material layer facing the first pole piece; the second insulating layer comprises a second base material layer and a second bonding layer, the second bonding layer being arranged on the surface of the second base material layer facing the first pole piece; The first base material layer and the second base material layer each independently comprise at least one of polyethylene terephthalate, polyimide, polypropylene or polyethylene; and / or, the first bonding layer and the second bonding layer each independently comprise at least one of acrylic resin, polypropylene, rubber or polyurethane.
11. The secondary battery according to any one of claims 1 to 10, characterized by In the thickness direction of the first pole piece, the thickness of the first insulating layer is T1, 10um≤T1≤31um, and / or, the thickness of the second insulating layer is T2, 10um≤T2≤31um.
12. The secondary battery according to any one of claims 1 to 11, characterized by The secondary battery further comprises a second tab, the second tab being electrically connected with the second pole piece; In the width direction of the secondary battery, the distance between the first tab and the second tab is D, 1.95mm≤D≤7.6mm.
13. The secondary battery according to any one of claims 1 to 12, characterized by The width of the secondary battery is W, 7mm≤W≤17mm.
14. An electronic device, comprising: A secondary battery comprising any one of the secondary batteries according to claims 1 to 13.