Secondary battery and electronic device

Abstract

The present application discloses a secondary battery and an electronic device. The secondary battery comprises an electrode assembly, the electrode assembly comprises a first electrode sheet, a separator, and a second electrode sheet which are stacked and wound, and the first electrode sheet comprises a first current collector and a first active material layer. A first groove exposing the first current collector is formed in the first active material layer, and a first tab is welded in the first groove and extends out of the electrode assembly in a first direction. The electrode assembly further comprises a first insulating layer and a second insulating layer; the first insulating layer is bonded to the first active material layer and covers the first tab; the separator comprises a first separator layer arranged adjacent to the first insulating layer in a second direction perpendicular to the first direction; the second electrode sheet comprises a first electrode sheet layer arranged adjacent to the first separator layer in the second direction; the second insulating layer is arranged between the first separator layer and the first electrode sheet layer, and is bonded to the first separator layer and the first electrode sheet layer; and the second insulating layer overlaps the first insulating layer in the second direction.

Description

Secondary batteries and electronic devices Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries are widely used in electric vehicles and consumer electronics due to their high energy density, high output power, and long cycle life. However, lithium-ion secondary batteries are prone to lithium deposition during cycling. This deposition not only degrades battery performance and significantly shortens cycle life, but also limits the battery's fast-charging capacity and can potentially lead to catastrophic consequences such as combustion and explosion.

[0003] Summary of the Invention

[0004] One purpose of the present application is to provide a secondary battery and an electronic device that can improve the lithium plating phenomenon.

[0005] In a first aspect, the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising a first electrode sheet, a separator, and a second electrode sheet that are stacked and wound together, the electrode assembly further comprising a first electrode tab and a second electrode tab, the first electrode sheet comprising a first current collector and a first active material layer that are stacked together. The first active material layer is provided with a first groove that exposes the first current collector, the first electrode tab is welded to the first current collector in the first groove and extends out of the electrode assembly along a first direction. The electrode assembly further comprises a first insulating layer and a second insulating layer, the first insulating layer being bonded to the first active material layer and covering the first electrode tab, the separator comprising a first separator layer disposed adjacent to the first insulating layer in a second direction perpendicular to the first direction, the second electrode sheet comprising a first electrode sheet layer disposed adjacent to the first separator layer in the second direction, the second direction being the thickness direction of the electrode assembly, the second insulating layer being disposed between the first separator layer and the first electrode sheet layer and bonding the first separator layer and the first electrode sheet layer, the second insulating layer overlapping the first insulating layer in the second direction.

[0006] This application improves the stability of the relative position of the second insulating layer and the first pole piece by configuring a second insulating layer that adheres the first diaphragm layer and the first pole piece layer and overlaps with the first insulating layer, thereby reducing the risk of lithium plating in the area corresponding to the first insulating layer. In addition, during the external short-circuit test, the temperature rise at the first pole piece is relatively high, which can easily transfer heat to the adjacent diaphragm, causing the diaphragm to shrink, and then causing an internal short circuit, accelerating heat generation, and even the risk of combustion and explosion. By providing a second insulating layer to bond the diaphragm and the pole piece, it can play a role in fixing the diaphragm, reducing the risk of shrinkage of the diaphragm adjacent to the first pole piece during the external short-circuit test, and improving safety performance.

[0007] In some embodiments, the first electrode is a negative electrode, the second electrode is a positive electrode, and along the second direction, the projection of the first insulating layer on the second insulating layer is located in the second insulating layer, so that the CB value of the area where the first electrode is located is greater than 1, which is beneficial to improving the lithium plating problem at the location of the first electrode.

[0008] In some embodiments, along the first direction, the length of the second insulating layer is L1, the width of the first electrode layer is L2, and L1 / L2 is 0.30-0.50, which helps to improve lithium deposition or short circuit problems. Further, L1 / L2 is 0.32-0.40.

[0009] In some embodiments, along a third direction perpendicular to the first and second directions, the width of the second insulating layer is W1, the width of the first tab is W2, and W1 / W2 is 2.00 to 4.00, which helps to improve lithium deposition or short circuit issues. Furthermore, W1 / W2 is 2.50 to 3.50.

[0010] In some embodiments, the second electrode sheet includes a second current collector and a second active material layer stacked together, the second active material layer having a second groove exposing the second current collector, the second electrode tab being welded to the second current collector in the second groove, the electrode assembly further including a third insulating layer and a fourth insulating layer, the third insulating layer being bonded to the second active material layer and covering the second electrode tab, the diaphragm further including a second diaphragm layer disposed adjacent to the third insulating layer in the second direction, the first electrode sheet including a second electrode sheet layer disposed adjacent to the second diaphragm layer in the second direction, the fourth insulating layer being disposed between the second diaphragm layer and the second electrode sheet layer and bonding the second diaphragm layer and the second electrode sheet layer, the fourth insulating layer overlapping the third insulating layer in the second direction. Such a configuration improves the stability of the relative position of the fourth insulating layer and the second electrode tab and reduces the risk of lithium plating at the location of the second electrode tab.

[0011] In some embodiments, the first electrode is a negative electrode, the second electrode is a positive electrode, and along the second direction, the projection of the fourth insulating layer on the third insulating layer is located in the third insulating layer, so that the CB value of the area where the second electrode is located is greater than 1, which is beneficial to improving the lithium plating problem at the location of the second electrode.

[0012] In some embodiments, along the first direction, the length of the fourth insulating layer is L3, the width of the second electrode layer is L4, and L3 / L4 is 0.20-0.45, which is beneficial to improving lithium deposition or short circuit problems. Further, L3 / L4 is 0.25-0.40.

[0013] In some embodiments, along a third direction perpendicular to the first and second directions, the width of the fourth insulating layer is W3, the width of the second tab is W4, and W3 / W4 is 1.30 to 3.50, which helps to improve lithium deposition or short circuit issues. Furthermore, W3 / W4 is 2.00 to 3.00.

[0014] In some embodiments, the second insulating layer includes a first adhesive layer, a base material layer, and a second adhesive layer stacked in sequence, the first adhesive layer is bonded to the first diaphragm layer, and the second adhesive layer is bonded to the first pole piece layer.

[0015] In some embodiments, the peel strength between the first adhesive layer and the first diaphragm layer is greater than the peel strength between the second adhesive layer and the first electrode layer, so that the second insulating layer remains adhered to the first diaphragm layer when impacted, maintaining the stability of the relative position of the second insulating layer and the first electrode, which helps reduce the risk of lithium plating.

[0016] In some embodiments, the substrate layer includes ceramic particles, which reduces the risk of thermal shrinkage of the first separator layer and helps to improve the lithium plating problem.

[0017] In some embodiments, along the second direction, the thickness of the second insulating layer is 20-50 μm, the thickness of the substrate layer is 10-30 μm, and the thickness of the first adhesive layer and / or the second adhesive layer is 5-20 μm.

[0018] In some embodiments, the separator includes a laminated porous base membrane and a ceramic layer. The ceramic layer is disposed on the surface of the porous base membrane facing the second electrode, and the first adhesive layer is bonded to the ceramic layer. The ceramic layer can enhance the heat resistance of the porous base membrane and reduce the risk of shrinkage. Furthermore, the bonding of the ceramic layer to the first adhesive layer can reduce the first adhesive layer's effect on the pore channels of the porous base membrane, thereby improving cycling performance.

[0019] In some embodiments, a third groove is provided on the first electrode layer, and the second insulating layer overlaps with the third groove in the second direction, so that the electrode diaphragm interface around the second insulating layer tends to be flat, reducing the risk of lithium plating.

[0020] A second aspect of the present application provides an electronic device comprising any of the above-mentioned secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is a schematic diagram of a secondary battery provided in one embodiment of the present application viewed along a second direction.

[0022] FIG2 is a schematic diagram of an electrode assembly provided in one embodiment of the present application observed along a first direction.

[0023] FIG3 is an enlarged view of point III shown in FIG2 .

[0024] FIG4 is a schematic diagram of the unfolded first pole piece and the second pole piece provided in one embodiment of the present application.

[0025] FIG5 is a schematic diagram of the unfolded first pole piece and the second pole piece provided in another embodiment of the present application.

[0026] FIG6 is a schematic cross-sectional view of an insulating layer provided in one embodiment of the present application.

[0027] FIG7 is a partial schematic diagram of an electrode assembly provided in one embodiment of the present application.

[0028] FIG8 is a schematic cross-sectional view of a diaphragm provided in one embodiment of the present application.

[0029] Description of main component symbols

[0030] Secondary battery 100

[0031] Housing 10

[0032] Electrode assembly 20

[0033] Electrode terminal 30

[0034] Main body 11

[0035] Packaging unit 12

[0036] Second pole piece 21

[0037] First pole piece 22

[0038] Diaphragm 23

[0039] Second current collector 211

[0040] Second active material layer 212

[0041] Second tab 213

[0042] First current collector 221

[0043] First active material layer 222

[0044] First tab 223

[0045] First groove 222a

[0046] First edge 222b

[0047] Second edge 222c

[0048] First insulating layer 24

[0049] First diaphragm layer 23a

[0050] First pole piece layer 21a

[0051] Second insulating layer 25

[0052] The third insulating layer 26

[0053] Second diaphragm layer 23b

[0054] Fourth insulating layer 27

[0055] Second pole piece layer 22a

[0056] Second groove 212a

[0057] First adhesive layer 251

[0058] Base material layer 252

[0059] Second adhesive layer 253

[0060] The third groove 212b

[0061] Fourth groove 222d

[0062] First direction X

[0063] The second direction Z

[0064] The third direction Y

[0065] The following specific implementation methods will further illustrate the present application in conjunction with the above-mentioned drawings. DETAILED DESCRIPTION

[0066] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0067] Below, embodiments of the present application will be described in detail. However, the present application may be embodied in many different forms and should not be construed as limited to the exemplary embodiments illustrated herein. Rather, these exemplary embodiments are provided to make the present application thorough and detailed for those skilled in the art.

[0068] In addition, for the sake of brevity and clarity, the size or thickness of various components, layers may be amplified in the accompanying drawings. Throughout the text, the same numerical value refers to the same element. As used herein, the terms "and / or" and "and / or" include any and all combinations of one or more related enumerated items. In addition, it should be understood that when element A is referred to as "connecting" element B, or when element A is referred to as "connecting" to element B, element A may be directly connected to element B, or there may be an intermediate element C and element A and element B may be indirectly connected to each other.

[0069] Further, when describing embodiments of the present application, the use of “may” refers to “one or more embodiments of the present application.”

[0070] The technical terms used herein are for the purpose of describing specific embodiments and are not intended to limit this application. As used herein, the singular is intended to include the plural, unless the context clearly indicates otherwise. It should be further understood that the term "comprising", when used in this specification, refers to the presence of the described features, values, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, values, steps, operations, elements, components and / or combinations thereof.

[0071] It should be understood that although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are used to distinguish one element, component, region, layer, or part from another element, component, region, layer, or part. Therefore, the first element, component, region, layer, or part discussed below may be referred to as the second element, component, region, layer, or part without departing from the teachings of the exemplary embodiments.

[0072] Referring to Figures 1 and 2, an embodiment of the present application provides a secondary battery 100, comprising a housing 10, an electrode assembly 20, an electrolyte, and a plurality of electrode terminals 30. The electrode assembly 20 and the electrolyte are contained in the housing 10. The electrode terminal 30 is connected to the electrode assembly 20 and extends from one side of the housing 10 along a first direction X to connect to external components. In this embodiment, the number of electrode terminals 30 is three, and the three electrode terminals 30 are configured as two positive electrodes and one negative electrode. By parallel shunting, the temperature rise of the electrode assembly 20 can be reduced. In other embodiments, the three electrode terminals 30 can be configured as two negative electrodes and one positive electrode, and the number of electrode terminals 30 can be two or more than three.

[0073] The housing 10 can be a packaging bag encapsulated with an encapsulating film (such as an aluminum-plastic film or a steel-plastic film), that is, the secondary battery 100 is a soft-pack battery. Specifically, the housing 10 includes a main body 11 and an encapsulating portion 12. The main body 11 is provided with a cavity for accommodating the electrode assembly 20. The encapsulating portion 12 extends from the edge of the main body 11 and is used to encapsulate the main body 11. The electrode terminal 30 extends through the encapsulating portion 12 along the first direction X. In other embodiments, the housing 10 is a metal housing, such as a steel shell or an aluminum shell.

[0074] Referring to Figures 1 and 2, the electrode assembly 20 includes a first electrode sheet 22, a separator 23, and a second electrode sheet 21 stacked and wound together. The separator 23 is disposed between the second electrode sheet 21 and the first electrode sheet 22. Specifically, the electrode assembly 20 is formed by stacking the second electrode sheet 21, the separator 23, and the first electrode sheet 22 in sequence along a second direction Z perpendicular to the first direction X and then winding them together. The electrode assembly 20 also includes a first electrode tab 223 and a second electrode tab 213. The first electrode tab 223 is connected to the first electrode sheet 22 and extends out of the electrode assembly 20 along the first direction X to connect to the corresponding electrode terminal 30. The second electrode tab 213 is connected to the second electrode sheet 21 and extends out of the electrode assembly 20 along the first direction X to connect to the corresponding electrode terminal 30. The first electrode sheet 22 and the second electrode sheet 21 have different polarities. In this embodiment, the first electrode sheet 22 is a negative electrode sheet, and the second electrode sheet 21 is a positive electrode sheet. In other embodiments, the first electrode sheet 22 is a positive electrode sheet, and the second electrode sheet 21 is a negative electrode sheet.

[0075] Referring to Figure 2 , the first electrode sheet 22 includes a stacked first current collector 221 and a first active material layer 222. The first active material layer 222 is disposed on at least one surface of the first current collector 221. The first electrode sheet 22 is a negative electrode sheet. The first current collector 221 and the first tab 223 may be made of copper foil, copper alloy foil, or the like. The first active material layer 222 includes a first active material, which may be selected from at least one of graphite materials, alloy materials, lithium metal, and alloys thereof. The graphite material may be selected from at least one of artificial graphite and natural graphite; the alloy material may be selected from at least one of silicon, silicon oxide, tin, and titanium sulfide. The first active material layer 222 may also include a conductive agent and a binder. The conductive agent may include at least one of conductive carbon black, carbon nanotubes, carbon fibers, or graphene; and the binder may include at least one of styrene-butadiene rubber, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, or sodium carboxymethyl cellulose.

[0076] Referring to Figures 2, 3, and 4, the first active material layer 222 is provided with a first groove 222a that exposes the first current collector 221, and the first tab 223 is welded in the first groove 222a. The first tab 223 and the first groove 222a can be interference-fitted to completely cover the first current collector 221 exposed in the first groove 222a, or can be gap-fitted to expose a portion of the first current collector 221, and this application is not limited thereto. In this embodiment, the first active material layer 222 is disposed on two opposing surfaces of the first current collector 221, each first active material layer 222 is provided with a first groove 222a, and the first tab 223 is welded in one of the first grooves 222a. In other embodiments, the first active material layer 222 is only disposed on one surface of the first current collector 221, or the first groove 222a is only disposed on one of the two first active material layers 222.

[0077] The first active material layer 222 includes a first edge 222b and a second edge 222c that are opposite to each other in the first direction X. The first groove 222a extends along the first direction X, penetrates the first edge 222b, and is separated from the second edge 222c. In other embodiments, the first groove 222a extends along the first direction X, penetrates the first edge 222b and the second edge 222c. There are many ways to form the first groove 222a, one of which is to first attach an easy-tear film or a heat-expandable film to the fixed position of the tab of the first current collector 221, then continuously apply the first active material slurry to the surface of the first current collector 221, and finally remove the easy-tear film or the heat-expandable film to form the first groove 222a that exposes the first current collector 221.

[0078] Because the first electrode tab 223 is welded to the first current collector 221, a weld mark (not shown) is formed between the first electrode tab 223 and the first current collector 221. The weld mark burr may pierce the diaphragm 23, causing the second electrode sheet 21 and the first electrode sheet 22 to short-circuit. In other embodiments, the first electrode tab 223 is connected to the first current collector 221 by a non-welding method, for example, the first electrode tab 223 is formed on the first current collector 221 by cutting. In this case, when the surface of the first electrode tab 223 is rough and uneven, or burrs appear around the first electrode tab 223, the diaphragm 23 may be pierced by the uneven surface or burrs, causing the second electrode sheet 21 and the first electrode sheet 22 to short-circuit. The electrode assembly 20 also includes a first insulating layer 24. The first insulating layer 24 is bonded to the first active material layer 222 and covers the first electrode tab 223 to reduce the risk of the first electrode tab 223 piercing the diaphragm 23, causing the second electrode sheet 21 and the first electrode sheet 22 to short-circuit. In this embodiment, there are two first insulating layers 24 , one of which is located on the same side of the first current collector 221 and the first electrode tab 223 in the second direction Z, and the other is located on opposite sides of the first current collector 221 in the second direction Z. In other embodiments, only one first insulating layer 24 is provided, which is located on the same side of the first current collector 221 in the second direction Z as the first electrode tab 223 .

[0079] In the electrode assembly 20, the wound separator 23 includes a first separator layer 23a disposed adjacent to the first insulating layer 24 in the second direction Z. The wound second electrode sheet 21 includes a first electrode sheet layer 21a disposed adjacent to the first separator layer 23a in the second direction Z. In the present application, in the second direction Z, there is no separator between the first insulating layer 24 and the first separator layer 23a, and no electrode sheet between the first separator layer 23a and the first electrode sheet layer 21a. The electrode assembly 20 also includes a second insulating layer 25. The second insulating layer 25 is disposed between the first separator layer 23a and the first electrode sheet layer 21a and bonds the first separator layer 23a and the first electrode sheet layer 21a. In the second direction Z, the second insulating layer 25 overlaps with the first insulating layer 24. A first groove 222a and a first insulating layer 24 are provided in the first active material layer 222. The lithium released from the second electrode 21 corresponding to the position of the first groove 222a and the first insulating layer 24 will not be received by the negative electrode, resulting in a lithium plating problem. By providing a second insulating layer 25 overlapping with the first insulating layer 24 and bonded to the first electrode layer 21a between the first diaphragm layer 23a adjacent to the first insulating layer 24 and the first electrode layer 21a, the lithium that can be released from the area where the first electrode layer 21a corresponding to the first insulating layer 24 is located is reduced, thereby reducing the risk of lithium plating. In addition, the second insulating layer 25 is bonded to the first diaphragm layer 23a and the first electrode layer 21a, which improves the stability of the relative position of the second insulating layer 25 and the first pole ear 223 compared to the case where the second insulating layer 25 is only bonded to the first electrode layer 21a, thereby further reducing the risk of lithium plating in this area. Furthermore, by providing the second insulating layer 25, a channel gap is formed between the first diaphragm layer 23a and the first electrode layer 21a, thereby improving the electrolyte infiltration effect and improving the problem of lithium deposition on the electrode caused by poor electrolyte infiltration. It should be noted that in Figure 3, in order to more clearly show the positional relationship of each component, the bonding of each insulating layer to the corresponding active material layer, diaphragm and / or electrode is not shown. The bonding relationship between each insulating layer and the corresponding active material layer, diaphragm and / or electrode is shown in the partial enlarged view of Figure 4.

[0080] Referring to FIG. 4 , in some embodiments, along the second direction Z, the projection of the first insulating layer 24 on the second insulating layer 25 is located within the second insulating layer 25 . In other words, when viewed along the second direction Z, the second insulating layer 25 completely covers the first insulating layer 24 . In this way, the CB value of the area where the first tab 223 is located is greater than 1, which helps to improve the lithium plating problem. The CB (Cell Balance) value represents the ratio of the negative electrode capacity to the positive electrode capacity per unit area. When the CB value is greater than 1, it means that the negative electrode capacity per unit area is greater than the positive electrode capacity, and lithium ions theoretically will not be precipitated; when the CB value is less than 1, it means that the negative electrode capacity per unit area is less than the positive electrode capacity. At this time, some of the lithium ions released from the positive electrode are not embedded in the negative electrode but are precipitated on the surface of the negative electrode; when the CB value is equal to 1, it means that the positive electrode capacity is equal to the negative electrode capacity, and lithium ions can theoretically be completely embedded in the negative electrode without precipitation. In some embodiments, along the first direction X, the length of the second insulating layer 25 is L1, the width of the first pole piece layer 21a is L2, and L1 / L2 is 0.30 to 0.50. In the present application, in the first direction X, the width of the first pole piece layer 21a is the same as the width of the first pole piece. When L1 / L2 is less than 0.30, the second insulating layer 25 may not completely cover the first insulating layer 24 in the first direction X, resulting in lithium deposition; or the second insulating layer 25 may not completely cover the first groove 222a in the first direction X, resulting in a short circuit. When L1 / L2 is greater than 0.50, the size of the second insulating layer 25 is too large, resulting in a large loss of energy density. Preferably, L1 / L2 is 0.32 to 0.40, which has a better effect of improving lithium deposition and increasing energy density.

[0081] In some embodiments, along a third direction Y perpendicular to the first direction X and the second direction Z, the width of the second insulating layer 25 is W1, the width of the first electrode 223 is W2, and W1 / W2 is 2.00 to 4.00. When W1 / W2 is less than 2.00, the second insulating layer 25 may not completely cover the first insulating layer 24 in the third direction Y, resulting in lithium deposition; or the second insulating layer 25 may not completely cover the first groove 222a in the third direction Y, resulting in a short circuit. When W1 / W2 is greater than 4.00, the size of the second insulating layer 25 is too large, resulting in a large loss of energy density. Preferably, W1 / W2 is 2.50 to 3.50, which is better for improving lithium deposition and increasing energy density.

[0082] Referring to Figure 2 , the second electrode sheet 21 includes a second current collector 211, a second active material layer 212, and a second electrode tab 213. In this embodiment, there are two second electrode tabs 213. The second active material layer 212 is disposed on at least one surface of the second current collector 211. The second electrode sheet 21 is a positive electrode sheet. The second current collector 211 and the second electrode tab 213 may be made of aluminum foil, aluminum alloy foil, or the like. The second active material layer 212 includes a second active material, which may include at least one of lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium-rich manganese-based materials, lithium nickel cobalt aluminum oxide, and combinations thereof. The second active material layer 212 may also include a conductive agent and a binder. The conductive agent may include at least one of conductive carbon black, carbon nanotubes, carbon fibers, or graphene. The binder may include at least one of styrene-butadiene rubber, polyvinyl alcohol, polytetrafluoroethylene, polyvinylidene fluoride, or sodium carboxymethyl cellulose.

[0083] Referring to Figures 2, 3, and 5, the second active material layer 212 is provided with a second groove 212a that exposes the second current collector 211, and the second tab 213 is welded to the second groove 212a. The second tab 213 and the second groove 212a can have an interference fit to completely cover the second current collector 211 exposed in the second groove 212a, or can have a clearance fit to partially expose the second current collector 211, which is not limited in this application. In this embodiment, the second active material layer 212 is disposed on two opposing surfaces of the second current collector 211, each second active material layer 212 has a second groove 212a, and the second tab 213 is welded to one of the second grooves 212a. In other embodiments, the second active material layer 212 is disposed only on one surface of the second current collector 211, or the second groove 212a is disposed only on one of the two second active material layers 212. In other embodiments, the second tab 213 can be connected to the second current collector 211 by non-welding means.

[0084] The electrode assembly 20 also includes a third insulating layer 26. The third insulating layer 26 is bonded to the second active material layer 212 and covers the second electrode tab 213 to reduce the occurrence of puncture of the diaphragm 23 due to weld marks, rough and uneven surfaces, or burrs formed on the second electrode tab 213, thereby reducing the risk of contact and short circuit between the second electrode sheet 21 and the first electrode sheet 22. In this embodiment, there are two third insulating layers 26, one of which is located on the same side of the second current collector 211 in the second direction Z as the second electrode tab 213, and the other is located on opposite sides of the second current collector 211 in the second direction Z. In other embodiments, only one third insulating layer 26 is provided, which is located on the same side of the second current collector 211 in the second direction Z as the second electrode tab 213.

[0085] In the electrode assembly 20, the wound separator 23 further includes a second separator layer 23b disposed adjacent to the third insulating layer 26 in the second direction Z. The wound first electrode sheet 22 includes a second electrode sheet layer 22a disposed adjacent to the second separator layer 23b in the second direction Z. In the present application, in the second direction Z, there is no separator between the third insulating layer 26 and the second separator layer 23b, and no electrode sheet between the second separator layer 23b and the second electrode sheet layer 22a. The electrode assembly 20 further includes a fourth insulating layer 27. The fourth insulating layer 27 is disposed between the second separator layer 23b and the second electrode sheet layer 22a, bonding the second separator layer 23b and the second electrode sheet layer 22a. In the second direction Z, the fourth insulating layer 27 overlaps with the third insulating layer 26. By configuring the fourth insulating layer 27 that adheres the second diaphragm layer 23b and the second electrode layer 22a and overlaps with the third insulating layer 26, the risk of lithium plating at the location of the second electrode tab 213 is reduced and the electrolyte infiltration effect is improved.

[0086] Referring to FIG. 5 , in some embodiments, along the second direction Z, the projection of the fourth insulating layer 27 on the third insulating layer 26 is located within the third insulating layer 26. In other words, along the second direction Z, the third insulating layer 26 completely covers the fourth insulating layer 27. This allows the CB value in the region where the second tab 213 is located to be greater than 1, which helps alleviate the lithium plating problem.

[0087] In some embodiments, along the first direction X, the length of the fourth insulating layer 27 is L3, the width of the second pole piece layer 22a is L4, and L3 / L4 is 0.20-0.45. In the present application, in the first direction X, the width of the second pole piece layer 22a is the same as the width of the second pole piece 22. When L3 / L4 is less than 0.20, the size of the fourth insulating layer 27 is too small, and the fourth insulating layer 27 may not completely cover the second groove 212a in the first direction X, resulting in a short circuit. When L3 / L4 is greater than 0.45, the size of the fourth insulating layer 27 is too large, and the third insulating layer 26 may not completely cover the fourth insulating layer 27 in the first direction X, resulting in lithium deposition, and an oversized fourth insulating layer 27 may result in a large loss of energy density. Preferably, L3 / L4 is 0.25-0.40, which has a better effect of improving lithium deposition and energy density.

[0088] In some embodiments, along the third direction Y perpendicular to the first direction X and the second direction Z, the width of the fourth insulating layer 27 is W3, the width of the second pole ear 213 is W4, and W3 / W4 is 1.30 to 3.50. When W3 / W4 is less than 1.30, the size of the fourth insulating layer 27 is too small, and the fourth insulating layer 27 may not completely cover the first groove 222a in the third direction Y, resulting in a short circuit. When W3 / W4 is greater than 3.50, the size of the fourth insulating layer 27 is too large, and the third insulating layer 26 may not completely cover the fourth insulating layer 27 in the third direction Y, resulting in lithium deposition, and the oversized fourth insulating layer 27 leads to a large loss of energy density. Preferably, W3 / W4 is 2.00 to 3.00, which has a better effect of improving lithium deposition and energy density.

[0089] The first insulating layer 24 and the third insulating layer 26 both include a polymer. The polymer may include one or more of polypropylene, polyethylene, an ethylene-based elastomer, a propylene-based elastomer, a styrene-based elastomer, an ionomer resin, polyvinylidene fluoride, a vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, or polyethylene glycol. These polymers have excellent adhesive properties.

[0090] Referring to Figure 6 , the second insulating layer 25 includes a first adhesive layer 251, a base material layer 252, and a second adhesive layer 253 stacked in sequence. The first adhesive layer 251 is bonded to the first diaphragm layer 23a, and the second adhesive layer 253 is bonded to the first electrode layer 21a. The structure of the fourth insulating layer 27 is identical to that of the second insulating layer 25 and will not be further described here.

[0091] The substrate layer 252 is used to support the first adhesive layer 251 and the second adhesive layer 253. The substrate layer 252 includes a polymer, which includes at least one of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), phenolic resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin or polyurethane, and these polymers have good adhesion. In some embodiments, the substrate layer 252 also includes ceramic particles. The ceramic particles include at least one of silicon oxide, titanium oxide, zirconium oxide or aluminum oxide. By adding ceramic particles, the thermal stability of the substrate layer 252 is improved and the risk of thermal shrinkage of the first diaphragm layer 23a is reduced. Preferably, the ceramic particles are titanium oxide.

[0092] In some embodiments, the peel strength between the first adhesive layer 251 and the first diaphragm layer 23a is greater than the peel strength between the second adhesive layer 253 and the first electrode layer 21a. When subjected to an impact, the second adhesive layer 253 separates from the first electrode layer 21a to cushion the impact force. At the same time, the first adhesive layer 251 and the first diaphragm layer 23a maintain adhesion, ensuring the stability of the relative position of the second insulating layer 25 and the first electrode tab 223, which helps reduce the risk of lithium plating. In other embodiments, the peel strength between the first adhesive layer 251 and the first diaphragm layer 23a is equal to or less than the peel strength between the second adhesive layer 253 and the first electrode layer 21a.

[0093] In some embodiments, the first adhesive layer 251 is a hot melt adhesive, and the peel strength between the first adhesive layer 251 and the first diaphragm layer 23a is 0.05N / mm to 0.50N / mm. The first adhesive layer 251 includes at least one of polymethyl methacrylate, polyacrylic acid, polyacrylic acid salt, polyacrylonitrile, polyvinyl pyrrolidone, polyvinyl acetate, styrene-isoprene-styrene block copolymer, ethylene-vinyl acetate copolymer, or polyimide. The second adhesive layer 253 is a pressure-sensitive adhesive, and the peel strength between the second adhesive layer 253 and the first electrode layer 21a is 0.01N / mm to 0.20N / mm. The second adhesive layer 253 includes at least one of polyethylene oxide, acrylonitrile-styrene-butadiene copolymer, styrene-butadiene copolymer, polyvinyl alcohol, polyvinyl methyl ether, polyvinyl ethyl ether, polyvinylidene fluoride, polytetrafluoroethylene, polyhexafluoropropylene, polymethyl methacrylate, polypropylene, polyethylene, or polyamide.

[0094] In some embodiments, along the second direction Z, the thickness of the second insulating layer 25 is 20 to 50 μm. When the thickness of the second insulating layer 25 is within the above range, a sufficient gap is formed between the first diaphragm layer 23a and the first pole piece layer 21a, which is conducive to improving the electrolyte infiltration effect and improving the problem of pole piece lithium deposition caused by poor electrolyte infiltration. When the thickness of the second insulating layer 25 is greater than 50 μm, the area where the second insulating layer 25 is located is too thick, and the forces are uneven during hot pressing, causing the area where the first pole piece 223 is located to cause lithium deposition problems due to poor dynamics. When the thickness of the second insulating layer 25 is less than 20 μm, the gap is small and the infiltration effect is not obvious. Preferably, the thickness of the second insulating layer 25 is 22 to 32 μm.

[0095] In some embodiments, the thickness of the substrate layer 252 is 10 to 30 μm. When the thickness of the substrate layer 252 is less than 10 μm, solder burrs may pierce the second insulating layer 25, causing a short circuit in the positive first contact. When the thickness of the substrate layer 252 is greater than 30 μm, this is detrimental to economic efficiency. Preferably, the thickness of the substrate layer 252 is 12 to 15 μm.

[0096] In some embodiments, the thickness of the first adhesive layer 251 is 5 to 20 μm, and the thickness of the second adhesive layer 523 is 5 to 20 μm. When the adhesive layer thickness is less than 5 μm, the adhesive bond is poor; when the adhesive layer thickness is greater than 20 μm, adhesive overflow is likely to occur during hot pressing. Preferably, the adhesive layer thickness is 5 to 10 μm.

[0097] Referring to FIG. 7 , in some embodiments, a third groove 212b is provided in the second active material layer 212 of the first electrode layer 21a. The bottom of the third groove 212b is spaced a preset distance from the second current collector 211, and the second current collector 211 does not appear from the third groove 212b. In the second direction Z, the second insulating layer 25 at least partially overlaps with the third groove 212b, and the second insulating layer 25 is at least partially contained within the third groove 212b, reducing the impact of the second insulating layer 25 on the surrounding diaphragm-electrode interface, making the electrode-diaphragm interface around the second insulating layer 25 smoother, and reducing the risk of lithium plating. FIG. 7 shows a situation where the second insulating layer 25 completely overlaps with the third groove 212b in the second direction Z. In another embodiment, the bottom of the third groove 212b is the second current collector 211, and the second current collector 211 appears from the third groove 212b.

[0098] Referring to Figure 7, in some embodiments, a fourth groove 222d is provided in the first active material layer 222 of the second electrode layer 22a. The bottom of the fourth groove 222d is separated from the first current collector 221 by a predetermined distance, and the first current collector 221 does not appear from the fourth groove 222d. In the second direction Z, the fourth insulating layer 27 at least partially overlaps with the fourth groove 222d, and the fourth insulating layer 27 is at least partially contained within the fourth groove 222d, reducing the impact of the fourth insulating layer 27 on the surrounding diaphragm-electrode interface, making the electrode-diaphragm interface around the fourth insulating layer 27 smoother, and reducing the risk of lithium plating. Figure 7 shows a situation where the fourth insulating layer 27 completely overlaps with the fourth groove 222d in the second direction Z. In another embodiment, the bottom of the fourth groove 222d is the first current collector 221, and the first current collector 221 appears from the fourth groove 222d.

[0099] Referring to Figure 8 , in some embodiments, the separator 23 includes a laminated porous base membrane 231 and a ceramic layer 232. The ceramic layer 232 is disposed on the surface of the porous base membrane 231 facing the second electrode, and the first adhesive layer of the second insulating layer is bonded to the ceramic layer 232. The ceramic layer 232 enhances the heat resistance of the porous base membrane 231, reduces the risk of shrinkage, and improves safety. The bonding of the ceramic layer 232 to the first adhesive layer of the second insulating layer reduces the impact of the first adhesive layer on the pore channels of the porous base membrane 231, thereby improving cycling performance.

[0100] The porous base film 231 may include at least one of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), phenolic resin, melamine resin, unsaturated polyester resin, epoxy resin, silicone resin, or polyurethane. The ceramic layer 232 may include at least one of boehmite, silicon oxide, titanium oxide, zirconium oxide, or aluminum oxide.

[0101] One embodiment of the present application further provides an electronic device comprising any of the above-described secondary batteries. The electronic device of the present application may include, but is not limited to, a laptop computer, a pen-type computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household battery, and a lithium-ion capacitor.

[0102] The performance of the secondary battery provided in this application is described below through specific examples and comparative examples.

[0103] Example 1-1

[0104] Preparation of the positive electrode sheet: The positive electrode active material (lithium cobalt oxide), conductive agent (conductive carbon black and carbon nanotubes), and binder (polyvinylidene fluoride) are dissolved in N-methylpyrrolidone solution at a weight ratio of 97.5:1:1.5 to form a positive electrode slurry with a solid content of 75%. Using aluminum foil as a current collector, the positive electrode slurry is applied to the surface of the positive electrode current collector to form the positive electrode active material layer. The negative electrode sheet is then produced through cold pressing, cutting, and welding of the positive electrode tabs.

[0105] Preparation of the negative electrode sheet: The negative electrode active material (graphite), conductive agent (conductive carbon black), thickener (sodium carboxymethyl cellulose), and binder (styrene-butadiene rubber) are mixed in a mass ratio of 97.5:1:0.5:1. Deionized water is then added as a solvent and stirred to obtain a negative electrode slurry with a solid content of 50 wt%. Using copper foil as a current collector, the negative electrode slurry is applied to the surface of the negative electrode current collector to form the negative electrode active material layer. The negative electrode sheet is then cold pressed, cut, and welded to the negative electrode tabs.

[0106] Preparation of isolation film: Polyethylene film is selected as the isolation film.

[0107] Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate (PP), and vinylene carbonate (VC) are mixed in a weight ratio of 20:30:20:28:2 to obtain an organic solvent, and then the fully dried lithium salt LiPF6 and the organic solvent are mixed in a weight ratio of 8:92 to obtain an electrolyte.

[0108] Preparation of a lithium-ion battery: The positive electrode sheet, polyethylene separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrode sheets. A first insulating layer is bonded to the surface of the negative electrode tab, a second insulating layer is bonded to the surface of the first electrode sheet corresponding to the negative electrode tab, a third insulating layer is bonded to the surface of the positive electrode tab, and a fourth insulating layer is bonded to the surface of the second electrode sheet corresponding to the positive electrode tab. Winding is performed to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag and heat-pressed. After liquid injection and formation, the lithium-ion battery is obtained. The projection of the first insulating layer on the second insulating layer is located within the second insulating layer, and the projection of the fourth insulating layer on the third insulating layer is located within the third insulating layer. The second and fourth insulating layers each include a first adhesive layer, a base material layer, and a second adhesive layer stacked in layers.

[0109] Example 1-2 to Example 1-5

[0110] The difference from Example 1-1 is that the materials of the first adhesive layer, the base material layer, and the second adhesive layer are different. Specific parameters are shown in Table 1.

[0111] Comparative Examples 1 to 4

[0112] The difference from Example 1-1 is that the second insulating layer and the fourth insulating layer only include a laminated base material layer and an adhesive layer. Specific parameters are shown in Table 1.

[0113] High-temperature short-circuit and lithium deposition tests were performed on each embodiment and comparative example. The test results are shown in Table 1.

[0114] High temperature short circuit test:

[0115] At 25°C, let it rest for 5 minutes. Charge the lithium-ion battery to 4.50V at a constant current of 0.2C. Then, charge it to 0.025C at a constant voltage of 4.50V. Let it rest for 30 minutes. Perform a short-circuit test with a 60±20mΩ resistor at a test temperature of 57±2°C. Stop the test when the voltage drops below 0.1V or the temperature drops to ±10°C below the test temperature. The test passes if the sample does not ignite or explode, and the temperature does not exceed 150°C.

[0116] Lithium deposition test:

[0117] Place the test battery at a test temperature of 25°C for 30 minutes, and then charge it to 4.53V using the following charging steps:

[0118] (1) 4C CC to 4.3V, CV to 3.2C;

[0119] (2) 3.2C CC to 4.35V, CV to 2.5C;

[0120] (3) 2.5C CC to 4.4V, CV to 2C;

[0121] (4) 2C CC to 4.45V, CV to 1.5C;

[0122] (5) 1.5C CC to 4.53V, CV to 0.28C;

[0123] After standing for 30 minutes, discharge according to the following steps:

[0124] (1) 1.5C DC to 3.3V,

[0125] (2) 0.7C DC to 3V.

[0126] The above charge and discharge process is one cycle. After repeating 700 cycles, the battery is disassembled to obtain the negative electrode sheet. If any part of the negative electrode sheet is greater than or equal to 2mm 2 If lithium is deposited in the area, it is determined to be lithium deposition.

[0127] The peel strength test is as follows:

[0128] The peel strength between the adhesive layer and the electrode or separator was tested using a high-speed rail tensile tester according to GB / T 2792-2014, "Test Method for Peel Strength of Adhesive Tapes." The test procedure is as follows: The secondary battery is discharged to 3.0V, then disassembled. The second or fourth insulating layer and the electrode or separator bonded to it are removed as a whole. The electrolyte on the surface is wiped clean with dust-free paper. The strips are then cut into 5mm x 5mm strips. Along the length of the specimen, the electrode or separator side of the specimen is adhered to a steel plate using double-sided tape (Nitto 5000NS). Fix the steel plate in the corresponding position of the high-speed rail tensile testing machine, pull up the other end of the second insulating layer / fourth insulating layer of the sample that is not adhered to the pole piece or diaphragm, and place the sample in the chuck and clamp it. The angle between the pulled-up sample part and the steel plate in space is 180°. The chuck pulls the sample at a speed of 1±0.2mm / s. The average peel strength of the stable area is finally measured and recorded as the peel strength of the first adhesive layer / second adhesive layer, recorded as a, in N / mm.

[0129] Table 1

[0130] It can be seen from Table 1 that compared with Comparative Examples 1-4, in Examples 1-1 to 1-5, the second insulating layer / fourth insulating layer is bonded to the diaphragm and the electrode at the same time, and no lithium deposition occurs, and the ability to slowly improve lithium deposition is good. This is because the insulating layer is bonded to the diaphragm and the electrode at the same time, which improves the stability of the relative position of the insulating layer and the electrode tab.

[0131] As shown in Examples 1-2 through 1-5, a higher peel strength of the first adhesive layer than the second adhesive layer improves the high-temperature short-circuit test results. In Examples 1-5, where the first adhesive layer had a higher viscosity than the second adhesive layer, the high-temperature short-circuit test pass rate was 100%, demonstrating optimal high-temperature short-circuit performance.

[0132] Comparison of Examples 1-1, 1-4, and 1-5 shows that adding ceramic particles to the substrate layer improves the high-temperature short-circuit test results. Example 1-1, in which no ceramic particles are added to the substrate layer, has the worst high-temperature short-circuit test results.

[0133] Example 2-1 to Example 2-12

[0134] The difference from Example 1-1 is that at least one of the following: the length L1 of the second insulating layer, the width L2 of the first electrode layer, the length L3 of the fourth insulating layer, and the width L4 of the second electrode layer is different. Each example was subjected to high-temperature short-circuit and lithium deposition tests. The parameters and test results of the examples are shown in Table 2.

[0135] Table 2

[0136] It can be seen from Example 1-1 and Example 2-1 to Example 2-6 that when 0.30≤L1 / L2≤0.50, it has good high-temperature short-circuit performance and the ability to slowly decompose lithium. In Example 2-2, L1 / L2<0.30, the high-temperature short-circuit pass rate and the lithium deposition pass rate are both the lowest, because the second insulating layer that is too short in the first direction cannot completely cover the first insulating layer. In Example 2-6, L1 / L2>0.50, although the high-temperature short-circuit pass rate and the lithium deposition pass rate are both large, the size of the second insulating layer is too large, which will lead to a large energy density loss. It can be seen from Example 1-1, Example 2-3, and Example 2-4 that when 0.32≤L1 / L2≤0.40, it has both good high-temperature short-circuit performance and the ability to slowly decompose lithium, and has little effect on energy density.

[0137] It can be seen from Example 1-1 and Example 2-7 to Example 2-12 that when 0.20≤L3 / L4≤0.45, it has good high-temperature short-circuit performance and the ability to slowly decompose lithium. In Example 2-7, L3 / L4<0.20, the high-temperature short-circuit pass rate is the smallest, because the fourth insulating layer that is too short in the first direction cannot completely cover the second groove. In Example 2-12, L3 / L4>0.45, the lithium deposition pass rate is the largest, because the size of the fourth insulating layer is too large, resulting in the third insulating layer may not be able to completely cover the fourth insulating layer. It can be seen from Example 1-1 and Example 2-8 to Example 2-10 that when 0.25≤L3 / L4≤0.40, it has both good high-temperature short-circuit performance and the ability to slowly decompose lithium, and has little effect on energy density.

[0138] Example 3-1 to Example 3-13

[0139] The difference from Example 1-1 is that at least one of the width W3 of the fourth insulating layer, the width W4 of the second tab, the width W1 of the second insulating layer, and the width W2 of the first tab is different.

[0140] High-temperature short-circuit and lithium deposition tests were performed on each embodiment. The embodiment parameters and test results are shown in Table 3.

[0141] Table 3

[0142] It can be seen from Example 1-1 and Example 3-1 to Example 3-7 that when 2.00≤W1 / W2≤4.00, it has better high-temperature short-circuit performance and the ability to slowly decompose lithium. In Example 3-1, W1 / W2<2.00, the high-temperature short-circuit pass rate and the lithium deposition pass rate are both the lowest, because the second insulating layer that is too short in the third direction cannot completely cover the first insulating layer. In Example 3-7, W1 / W2>4.00, although the probability of the high-temperature short-circuit pass rate and the lithium deposition pass rate are both high, the size of the second insulating layer is too large, which will lead to a large loss of energy density. It can be seen from Example 1-1 and Example 3-3 to Example 3-5 that when 2.50≤W1 / W2≤3.50, it has both good high-temperature short-circuit performance and the ability to slowly decompose lithium, and has little effect on energy density.

[0143] It can be seen from Example 1-1, Example 3-8 to Example 3-13 that when 1.30≤W3 / W4≤3.50, it has good high-temperature short-circuit performance and the ability to slowly decompose lithium. In Example 3-8, W3 / W4<2.00, the high-temperature short-circuit pass rate is the lowest, because the fourth insulating layer that is too short in the third direction cannot completely cover the second groove. In Example 3-13, W3 / W4>3.50, the lithium deposition pass rate is the lowest, because the size of the fourth insulating layer is too large, resulting in the third insulating layer may not be able to completely cover the fourth insulating layer. It can be seen from Example 1-1, Example 3-10, and Example 3-11 that when 2.00≤W3 / W4≤3.00, it has both good high-temperature short-circuit performance and the ability to slowly decompose lithium, and has little effect on energy density.

[0144] Example 4-1 to Example 4-13

[0145] The difference from Example 1 is that at least one of the thicknesses of the insulating layer, the first adhesive layer, the substrate layer, and the second adhesive layer is different. Each example was subjected to high-temperature short-circuit and lithium deposition tests. The parameters and test results for each example are shown in Table 4.

[0146] Table 4

[0147] As shown in Table 4, when the thickness of the insulating layer is 20-50 μm, the thickness of the substrate layer is 10-30 μm, the thickness of the first adhesive layer is 5-20 μm, and the thickness of the second adhesive layer is 5-20 μm, good high-temperature short-circuit performance and slow lithium deposition are achieved. In Examples 3-9 to 3-11, the insulating layer thickness is less than 20 μm, resulting in poor high-temperature short-circuit performance. In Examples 3-12 and 3-15, the insulating layer thickness is greater than 50 μm. Although the high-temperature short-circuit pass rate and lithium deposition pass rate are relatively high, the excessive thickness of the insulating layer leads to a significant loss in energy density.

[0148] The above disclosure is only a preferred embodiment of the present application, and certainly cannot be used to limit the scope of rights of the present application. Therefore, equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A secondary battery comprising an electrode assembly, wherein the electrode assembly comprises a first electrode sheet, a separator, and a second electrode sheet stacked and wound together, the electrode assembly further comprising a first electrode tab and a second electrode tab, wherein the first electrode sheet comprises a first active material layer and a first current collector stacked together, A first groove is formed in the first active material layer to expose the first current collector, and the first electrode tab is welded to the first current collector in the first groove and extends out of the electrode assembly along a first direction; The electrode assembly also includes a first insulating layer and a second insulating layer, the first insulating layer is bonded to the first active material layer and covers the first electrode tab; the diaphragm includes a first diaphragm layer arranged adjacent to the first insulating layer in a second direction perpendicular to the first direction, and the second electrode piece includes a first electrode piece layer arranged adjacent to the first diaphragm layer in the second direction, and the second direction is the thickness direction of the electrode assembly; the second insulating layer is arranged between the first diaphragm layer and the first electrode piece layer and bonds the first diaphragm layer and the first electrode piece layer, and the second insulating layer overlaps with the first insulating layer in the second direction.

2. The secondary battery according to claim 1, wherein The first pole piece is a negative pole piece, the second pole piece is a positive pole piece, and along the second direction, the projection of the first insulating layer on the second insulating layer is located in the second insulating layer.

3. The secondary battery according to claim 2, wherein Along the first direction, the length of the second insulating layer is L1, the width of the first pole piece layer is L2, and L1 / L2 is 0.30-0.

50.

4. The secondary battery according to claim 3, wherein L1 / L2 is 0.32~0.

40.

5. The secondary battery according to claim 2, wherein Along a third direction perpendicular to the first direction and the second direction, the width of the second insulating layer is W1, the width of the first electrode tab is W2, and W1 / W2 is 2.00-4.

00.

6. The secondary battery according to claim 5, wherein W1 / W2 is 2.50~3.

50.

7. The secondary battery according to claim 1, wherein The second pole piece includes a second current collector and a second active material layer arranged in a stacked manner, a second groove exposing the second current collector is provided in the second active material layer, and the second pole tab is welded to the second current collector in the second groove. The electrode assembly also includes a third insulating layer and a fourth insulating layer, the third insulating layer is bonded to the second active material layer and covers the second pole tab, the diaphragm also includes a second diaphragm layer arranged adjacent to the third insulating layer in the second direction, the first pole piece includes a second pole piece layer arranged adjacent to the second diaphragm layer in the second direction, the fourth insulating layer is arranged between the second diaphragm layer and the second pole piece layer and bonds the second diaphragm layer and the second pole piece layer, and the fourth insulating layer overlaps with the third insulating layer in the second direction.

8. The secondary battery according to claim 7, wherein The first pole piece is a negative pole piece, the second pole piece is a positive pole piece, and along the second direction, the projection of the fourth insulating layer on the third insulating layer is located in the third insulating layer.

9. The secondary battery according to claim 8, wherein Along the first direction, the length of the fourth insulating layer is L3, the width of the second pole piece layer is L4, and L3 / L4 is 0.20-0.

45.

10. The secondary battery according to claim 9, wherein L3 / L4 is 0.25~0.

40.

11. The secondary battery according to claim 8, wherein Along a third direction perpendicular to the first direction and the second direction, the width of the fourth insulating layer is W3, the width of the second electrode tab is W4, and W3 / W4 is 1.30-3.

50.

12. The secondary battery according to claim 11, wherein W3 / W4 is 2.00~3.

00.

13. The secondary battery according to any one of claims 1 to 12, characterized in that: The second insulating layer includes a first adhesive layer, a base material layer, and a second adhesive layer stacked in sequence. The first adhesive layer is bonded to the first diaphragm layer, and the second adhesive layer is bonded to the first pole piece layer.

14. The secondary battery according to claim 13, wherein The peeling strength between the first adhesive layer and the first diaphragm layer is greater than the peeling strength between the second adhesive layer and the first pole piece layer.

15. The secondary battery according to claim 14, wherein The peel strength between the first adhesive layer and the first diaphragm layer is 0.05 N / mm to 0.50 N / mm, and the peel strength between the second adhesive layer and the first pole piece layer is 0.01 N / mm to 0.20 N / mm.

16. The secondary battery according to claim 13, wherein The substrate layer includes ceramic particles.

17. The secondary battery according to claim 13, wherein Along the second direction, the thickness of the second insulating layer is 20 μm to 50 μm, the thickness of the base material layer is 10 μm to 30 μm, and the thickness of the first adhesive layer and / or the second adhesive layer is 5 μm to 20 μm.

18. The secondary battery according to claim 13, wherein The diaphragm includes a porous base film and a ceramic layer which are stacked. The ceramic layer is arranged on a surface of the porous base film facing the second pole piece. The first adhesive layer is bonded to the ceramic layer.

19. The secondary battery according to any one of claims 1 to 18, wherein: A third groove is provided on the first pole piece layer, and in the thickness direction of the electrode assembly, the second insulating layer at least partially overlaps with the third groove.

20. An electronic device, characterized in that: Comprising the battery according to any one of claims 1 to 19.

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