Electrode assembly and secondary battery

Abstract

The present application relates to an electrode assembly and a secondary battery. A first electrode sheet comprises a first current collector and a first active material layer, the first current collector having a first surface facing a second electrode sheet, and the first active material layer being disposed on the first surface. The second electrode sheet comprises a second current collector and a second active material layer, the second current collector having a second surface facing the first active material layer, and the second active material layer being disposed on the second surface. The electrode assembly further comprises a first tab and a first adhesive layer. The first surface has a first bare foil region; the first bare foil region, the first active material layer, and a separator jointly enclose to form a first space; the first tab is partially disposed in the first space, the first adhesive layer is disposed on the surface of the first tab facing the first current collector so as to bond the first bare foil region to the first tab, and the other surface of the first tab is in contact with the separator. The electrode assembly and the secondary battery of the present application can reduce the risk of the separator being pierced, thereby making full use of space, and boosting energy density.

Description

Electrode assembly and secondary battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese Patent Application No. 202410702746.0, filed on May 31, 2024, and entitled "Electrode assembly and secondary battery", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of batteries, in particular to an electrode assembly and a secondary battery. BACKGROUND

[0004] The tab, as a bridge for the electrical connection between the secondary battery and the external circuit, is usually made of metal material. The tab is welded with the current collector inside the secondary battery, which can make the tab conductive with the electrode assembly inside the secondary battery, so as to achieve the purpose of transmitting current.

[0005] In order to facilitate the welding of the tab, a double-sided empty foil area is usually provided on the current collector, and the welding head and the welding seat are respectively in contact with the current collector in the two empty foil areas for welding. However, the welding of the tab and the empty foil area of the current collector usually produces partial welding burrs, which are easy to pierce the isolation film and cause the short circuit failure of the positive and negative electrode sheets inside the secondary battery. SUMMARY

[0006] The purpose of the present application is to provide an electrode assembly and a secondary battery, which aims to improve the technical problem that the current collector is easy to produce welding burrs and pierce the isolation film.

[0007] According to a first aspect of the present application, an electrode assembly is provided, comprising a first electrode sheet, an isolation film and a second electrode sheet, the isolation film being arranged between the first electrode sheet and the second electrode sheet. The first electrode sheet comprises a first current collector and a first active material layer, the first current collector having a first surface facing the second electrode sheet, and the first active material layer being arranged on the first surface. The second electrode sheet comprises a second current collector and a second active material layer, the second current collector having a second surface facing the first active material layer, and the second active material layer being arranged on the second surface. The electrode assembly further comprises a first tab and a first adhesive layer. The first surface has a first empty foil area, the first empty foil area, the first active material layer and the isolation film collectively enclosing a first space, the first tab being partially arranged in the first space, and the first adhesive layer being arranged on the surface of the first tab facing the first current collector to bond the first empty foil area and the first tab, the first empty foil area and the first tab being electrically connected, and the first tab being in contact with the isolation film away from the first current collector.

[0008] In the technical solution, the first tab is bonded to the first empty foil area through the first adhesive layer, without the need for a welding head and a welding seat, and without welding burrs, which can reduce the risk of the isolation film being punctured, and without the need for an insulating adhesive to cover the welding burrs, one layer of insulating adhesive is saved, the first tab can directly contact the isolation film, which not only reduces the risk of the isolation film being punctured, but also makes full use of space and facilitates the improvement of the energy density of the secondary battery.

[0009] In some preferred embodiments, the electrode assembly further comprises a second tab and a second adhesive layer, the second surface has a second empty foil area, the second empty foil area, the second active material layer and the isolation film jointly enclose a second space, the second tab is partially arranged in the second space, the second tab is partially arranged in the second space, and the second adhesive layer is arranged on the surface of the second tab facing the second current collector to bond the second empty foil area and the second tab, and the surface of the second tab away from the second current collector is in contact with the isolation film. The second tab is bonded to the second empty foil area through the second adhesive layer, without the need for welding through a welding head and a welding seat, and without welding burrs, so the fourth surface can also not need to be provided with an empty foil area, and the second tab can directly contact the isolation film, without the need for an insulating adhesive layer, space can be fully utilized, and the energy density of the secondary battery can be improved.

[0010] In some preferred embodiments, as viewed in the thickness direction of the first tab, the projection of the first empty foil area on the second tab is located in the second active material layer. Since the first tab is bonded to the first empty foil area through the first adhesive layer, there are no welding burrs, and the second tab does not need to be provided with tab adhesive on the second active material layer, the space utilization rate can be further improved, and the energy density of the secondary battery can be improved.

[0011] In some preferred embodiments, the surface of the first active material layer facing the second active material layer is provided with tab adhesive. As viewed in the thickness direction of the second tab, the projection of the second empty foil area on the first tab is located in the projection of the tab adhesive. The lithium ions of the first tab can be deintercalated at the tab adhesive, so that the second tab has sufficient excess capacity to intercalate the lithium ions deintercalated from the first tab, and the lithium precipitation of the secondary battery can be alleviated, wherein the first tab is a positive tab, and the second tab is a negative tab.

[0012] In some preferred embodiments, the surface of the first active material layer facing the second active material layer is provided with a third space, and the tab adhesive is at least partially accommodated in the third space. The tab adhesive does not occupy additional thickness space of the first tab, and the energy density of the secondary battery can be improved while reducing lithium precipitation of the secondary battery.

[0013] In some preferred embodiments, the first current collector further has a third surface, and the first surface is opposite to the third surface along the thickness direction of the first current collector. The first tab further has a third active material layer, and the third active material layer is arranged on the third surface. The projection of the first empty foil area falls on the projection of the third active material layer as viewed along the thickness direction of the first tab. That is, the position of the third surface corresponding to the first empty foil area does not need to remove the active material, and more third active material layer can be coated on the third surface to fully utilize the space and improve the energy density of the secondary battery.

[0014] In some preferred embodiments, the length of the first empty foil area along the width direction of the current collector is L1, and the length of the first adhesive layer along the width direction of the current collector is L2, 0mm≤L1-L2≤5mm. The tab is arranged in the first empty foil area along the width direction of the current collector, and a gap space of 0mm to 5mm is reserved along the width direction of the current collector, which can reduce the direct bonding of the first adhesive layer and the first active material layer, and further reduce the influence of the first adhesive layer on the energy density of the secondary battery. When L1-L2=0mm, the first adhesive layer can bond the first empty foil area in the length direction, thereby improving the bonding strength. When L1-L2≤5mm, the space occupied by the first adhesive layer can be reduced, thereby improving the energy density of the secondary battery. When L1-L2<0mm, the first adhesive layer may cover the active material, resulting in a loss of energy density.

[0015] Optionally, the width of the first empty foil area along the length direction of the current collector is W1, and the width of the first adhesive layer along the length direction of the current collector is W2, 0mm≤W1-W2≤5mm. The tab is arranged in the first empty foil area along the length direction of the current collector, and a gap space of 0mm to 5mm is reserved along the length direction of the current collector, which can reduce the direct bonding of the first adhesive layer and the first active material layer, and further reduce the influence of the first adhesive layer on the energy density of the secondary battery. Not only is it convenient for the tab to be arranged in the first empty foil area, but also it is convenient for the tab to be bonded and fixed to the current collector through the first adhesive layer. When W1-W2=0mm, the first adhesive layer can bond the first empty foil area in the width direction, thereby improving the bonding strength. When W1-W2≤5mm, the space occupied by the first adhesive layer can be reduced, thereby improving the energy density of the secondary battery.

[0016] In some preferred embodiments, the bonding length of the first adhesive layer and the first empty foil area along the width direction of the current collector is L3, 4mm≤L3≤24mm. The bonding width of the first adhesive layer and the first empty foil area along the length direction of the current collector is W3, 4mm≤W3≤14mm. Sufficient bonding length and bonding width can increase the bonding area of the first adhesive layer and the first empty foil area, improve the connection strength, and reduce the influence of the first adhesive layer on the energy density of the secondary battery.

[0017] Optionally, the thickness of the first adhesive layer is T1 along the thickness direction of the current collector, and 2 μm≤T1≤50 μm. The connection strength can be improved while reducing the influence of the first adhesive layer on the energy density of the secondary battery.

[0018] In some preferred embodiments, the length of the adhesion between the first adhesive layer and the first empty foil area along the width direction of the first pole piece is L3, and the length of the overlap between the first tab and the first current collector along the width direction of the first pole piece is L4, as viewed along the thickness direction of the first pole piece, and 50%L4≤L3≤150%L4; and / or, the width of the adhesion between the first adhesive layer and the first empty foil area along the length direction of the first pole piece is W3, and the width of the overlap between the first tab and the first current collector along the length direction of the first pole piece is W4, as viewed along the thickness direction of the first pole piece, and 50%W4≤W3≤150%W4. The connection strength between the tab and the current collector can be improved while reducing the influence of the first adhesive layer on the energy density of the secondary battery.

[0019] In some preferred embodiments, the first adhesive layer and the first active material layer have a gap space therebetween ， The direct adhesion between the first adhesive layer and the first active material layer is prevented, and the influence of the first adhesive layer on the capacity and energy density of the secondary battery is reduced.

[0020] In some preferred embodiments, the first adhesive layer comprises at least one of epoxy resin, polyolefin, polystyrene, polymethyl methacrylate, phenolic resin, or styrene-butadiene rubber. The above-mentioned materials have excellent adhesion and chemical corrosion resistance, and can adapt to various electrochemical reactions inside the secondary battery.

[0021] In some preferred embodiments, the first adhesive layer comprises a thermosetting adhesive, a hot melt adhesive, or a pressure sensitive adhesive. Part of the first tab penetrates through the first adhesive layer to contact the first empty foil area, so as to realize the electrical connection between the first tab and the first empty foil area.

[0022] In some preferred embodiments, the first adhesive layer is an electrically conductive adhesive layer, and the electrical connection between the first tab and the first empty foil area can be realized without the first tab penetrating through the first adhesive layer.

[0023] In a second aspect, the application further provides a secondary battery comprising the electrode assembly according to any one of the embodiments of the first aspect.

[0024] Additional layers and advantages of the embodiments of the application will be described, shown, or explained in part in the subsequent description, drawings, or by implementation of the embodiments of the application. BRIEF DESCRIPTION OF DRAWINGS

[0025] One or more embodiments are illustrated by way of example in the figures that are not intended to be limiting of the embodiments. Like references numerals have been used to describe substances throughout the specification and drawings that are similar in structure and / or function. Dimensions of components and / or materials could be arbitrarily shown in the figures without limiting the scope of the embodiments. The figures illustrate different structures of embodiments of the present application.

[0026] FIG. 1 is a schematic view of a layer structure of an electrode assembly according to some embodiments of the present application;

[0027] FIG. 2 is a schematic view 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 structure of a first tab according to some embodiments of the present application;

[0029] FIG. 4 is a partial enlarged view of A in FIG. 3;

[0030] FIG. 5 is a schematic view of bonding of a first tab, a first adhesive layer, and a first current collector according to some embodiments of the present application;

[0031] FIG. 6 is a schematic view of bonding of a first tab, a first adhesive layer, and a first current collector according to some embodiments of the present application;

[0032] FIG. 7 is a schematic view of bonding of a first tab, a first adhesive layer, and a first current collector according to some embodiments of the present application;

[0033] FIG. 8 is a schematic view of a layer structure of an electrode assembly according to some embodiments of the present application;

[0034] FIG. 9 is a schematic view of bonding of a first tab, a first adhesive layer, and a first current collector according to some embodiments of the present application;

[0035] FIG. 10 is a schematic view of bonding of a first tab, a first adhesive layer, and a first current collector according to some embodiments of the present application (viewed in a third direction Z);

[0036] FIG. 11 is a schematic view of a layer structure of an electrode assembly according to the prior art.

[0037] BRIEF DESCRIPTION OF DRAWINGS 100, electrode assembly; 10, first tab; 11, first current collector; 111, first surface; 112, third surface; 113, first empty foil area; 12, first active material layer; 13, third active material layer; 14, first space; 15, third space; 20, second tab; 21, second current collector; 211, second surface; 212, fourth surface; 213, second empty foil area; 22, second active material layer; 23, fourth active material layer; 15, second space; 30, separator; 40, first tab; 41, insertion groove; 42, protrusion; 50, first adhesive layer; 60, second tab; 70, second adhesive layer; 80, tab adhesive; X, first direction; Y, second direction; Z, third direction. DETAILED DESCRIPTION

[0038] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application.

[0039] In the present application, the phrase "embodiments" means that the specific features, structures or characteristics described in connection with the embodiments 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 embodiments, nor is it necessarily independent or alternative embodiments to other embodiments.

[0040] 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 "multiple" is more than two, unless otherwise explicitly and specifically limited.

[0041] 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 " / " in this paper generally represents that the front and rear associated objects are in an "or" relationship.

[0042] 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.

[0043] The tab, as a bridge for the electrical connection between the secondary battery and the external circuit, is usually made of metal material. The tab is welded with the current collector inside the secondary battery, which can make the tab conductive with the electrode assembly inside the secondary battery, so as to achieve the purpose of transmitting current.

[0044] Please refer to FIG. 11. In order to facilitate the welding of the positive tab 40a, a double-sided empty foil area (the empty foil area is an area on the current collector without an active material layer) is usually provided on the positive current collector 11a. The welding seat is in contact with the positive current collector 11a at one side of the empty foil area, and the welding head welds the positive tab 40a and the positive current collector 11a at the other side of the empty foil area. The negative tab 20a is usually also similarly provided.

[0045] However, the welding of the positive tab and the positive current collector 11a and the welding of the negative tab 60a and the negative current collector 21a usually has a partial welding burr, which is easy to pierce the separator 30a and cause the positive tab 10a and the negative tab 20a inside the secondary battery to be short-circuited and fail. To reduce the risk of the separator 30a being pierced, as shown in FIG. 11, a double-layer insulating adhesive 90 is usually needed to be arranged at the positive tab 40a, that is, a layer of insulating adhesive 90 is arranged on one side of the positive current collector 11a, and another layer of insulating adhesive 90 is also arranged on the other side. The same is true for the negative tab 20a. The arrangement of the double-layer insulating adhesive 90 prevents the burr from piercing the separator 30a.

[0046] In addition, two layers of tab adhesives 80a also need to be arranged on the positive tab 10a to reduce the influence of the burr at the negative tab 60a on the positive active material layer 12a. Two layers of tab adhesives 80a also need to be arranged on the negative tab 20a to reduce the influence of the burr at the positive tab 40a on the negative active material layer 22a. However, the arrangement of multiple layers of adhesives also affects the energy density of the secondary battery.

[0047] To improve the above problems, the first aspect of the present application proposes an electrode assembly 100, which is a place where the secondary battery generates an electrochemical reaction and can store and release electric energy. The electrode assembly 100 includes a first tab 10, a separator 30, a second tab 20, a first tab 40, a first adhesive layer 50, a second tab 60, and a second adhesive layer 70.

[0048] Please refer to FIG. 1. The electrode assembly 100 adopts a tab shape, that is, the first tab 10 and the second tab 20 are alternately and layeringly arranged, and the separator 30 is arranged between adjacent first tab 10 and second tab 20. In some embodiments, only one first tab 10 and one second tab 20 are layeringly arranged. In other embodiments, a plurality of first tabs 10 and second tabs 20 are alternately and layeringly arranged.

[0049] In other embodiments, the electrode assembly 100 adopts a winding shape, that is, the first tab 10, the separator 30, and the second tab 20 are layeringly and windingly arranged, and the separator 30 is arranged between the first tab 10 and the second tab 20 to separate them.

[0050] The first tab 40 can be bonded to the first tab 10 through the first adhesive layer 50. The first tab 40 can lead the current flowing through the first tab 10 to an external circuit or lead the external current to the first tab 10. The second tab 60 can be bonded to the second tab 20 through the second adhesive layer 70. The second tab 20 can lead the current flowing through the second tab 20 to an external circuit or lead the external current to the second tab 20 to realize the charging and discharging of the secondary battery.

[0051] For the first tab 10 described above, please refer to FIG. 1. The first tab 10 includes a first current collector 11, a first active material layer 12, and a third active material layer 13. The first current collector 11 has a first surface 111 and a third surface 112 arranged oppositely along the thickness direction (third direction Z) of the first current collector 11. The first active material layer 12 is arranged on the first surface 111, and the third active material layer 13 is arranged on the third surface 112.

[0052] Taking the first tab 10 as a positive electrode tab as an example, the first current collector 11 as the conductive substrate of the first tab 10 can be an aluminum foil, a copper foil, or a nickel foil, etc. in a whole flat and strip-shaped structure. Taking the aluminum foil as an example, the aluminum foil has high conductivity, which can effectively reduce the internal resistance of the secondary battery, and facilitate to improve the energy density and power density of the secondary battery. In addition, the aluminum foil also has good mechanical strength, which can withstand the expansion and contraction of the secondary battery during the charging and discharging process, and ensure the stability and safety of the secondary battery.

[0053] The first active material layer 12 and the third active material layer 13 each include a positive electrode active material, a conductive agent, and a binder, etc. After the above-mentioned material components are mixed and stirred uniformly, they are coated on the first surface 111 and the third surface 112 of the first current collector 11, thereby obtaining the first active material layer 12 and the third active material layer 13. The positive electrode active material can be selected from one or more of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium manganese iron phosphate, and cobalt-free material.

[0054] In some embodiments, the first current collector 11 has a region without the active material layer coated thereon, for example, please refer to FIG. 1 and FIG. 5. The first surface 111 has a first empty foil area 113, which is a region of the first current collector 11 without the active material layer coated thereon. The third surface 112 can also be provided with a third empty foil area (not labeled in the figure). The double-sided empty foil area is provided, and the welding seat can receive the first current collector 11 in the third empty foil area, and the welding head welds the first tab 40 and the first current collector 11 in the first empty foil area 113.

[0055] In the embodiments of the present application, the first tab 40 is bonded to the first empty foil area 113 through the first adhesive layer 50, and does not need a welding head and a welding seat, and there is no welding burr. Therefore, the third surface 112 does not need to be provided with an empty foil area, that is, the third surface 112 at the position corresponding to the first empty foil area 113 does not need to remove the active material. For example, as observed along the thickness direction (third direction Z) of the first tab 10, the projection of the first empty foil area 113 falls on the projection of the third active material layer 13, and more third active material layer 13 can be coated on the third surface 112, so as to make full use of the space and improve the energy density of the secondary battery.

[0056] For the second tab 20, please refer to FIG. 1, the second tab 20 includes a second current collector 21, a second active material layer 22, and a fourth active material layer 23. Along the thickness direction (third direction Z) of the second current collector 21, the second current collector 21 has oppositely arranged second and fourth surfaces 211 and 212, the second active material layer 22 is arranged on the second surface 211, and the fourth active material layer 23 is arranged on the fourth surface 212. When the first tab 10 and the second tab 20 are stacked, the first surface 111 faces the second tab 20, and the second surface 211 faces the first tab 10.

[0057] Taking the second tab 20 as a negative electrode tab as an example, the second current collector 21 can be an aluminum foil, a copper foil, or a nickel foil, etc. in a whole flat and strip-shaped structure. Taking the copper foil as an example, the copper foil has high conductivity, which can effectively reduce the internal resistance of the secondary battery. In addition, the aluminum foil also has good mechanical strength, which can withstand the expansion and contraction of the secondary battery during the charging and discharging process, thereby ensuring the stability and safety of the secondary battery.

[0058] The second and fourth active material layers 22 and 23 include a negative electrode active material, a conductive agent, and a binder, etc. After the above-mentioned material components are mixed and stirred uniformly, they are coated on the second and fourth surfaces 211 and 212 of the second current collector 21, thereby obtaining the second and fourth active material layers 22 and 23. The negative electrode active material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber, elemental silicon, silicon oxide compounds, and silicon alloys.

[0059] In some embodiments, the second current collector 21 has an area without the active material layer coated thereon, for example, please refer to FIG. 1, the second surface 211 has a second uncoated foil area 213, which is an area of the second current collector 21 without the active material layer coated thereon.

[0060] In the embodiments of the present application, the second lug 60 is bonded to the second uncoated foil area 213 through the second adhesive layer 70, without the need for welding through the welding head and the welding seat, and there is no welding burr, so the fourth surface 212 also does not need to be provided with an uncoated foil area. For example, along the thickness direction (third direction Z) of the second tab 20, the projection of the second uncoated foil area 213 falls on the projection of the fourth active material layer 23, thereby fully utilizing the space and improving the energy density of the secondary battery.

[0061] It can be understood that when the electrode assembly 100 adopts a winding structure, the first tab 10 is wound along the length direction (the first direction X) thereof, and after winding, there are multiple thickness directions of the first current collector 11. In the embodiments of the present application, it is generally referred to as observing along the thickness direction of the corresponding place, for example, "observing along the thickness direction of the second tab 20, the projection of the second empty foil area 213 falls on the projection of the fourth active material layer 23", here it is observed along the thickness direction of the second tab at the second empty foil area 213.

[0062] For the above-mentioned isolation film 30, please refer to FIG. 1 and FIG. 2, the isolation film 30 is arranged between the first tab 10 and the second tab 20, and is used to insulate and separate the first tab 10 and the second tab 20. The isolation film 30 can adopt a PE isolation film or a PP isolation film containing ceramic, etc. In some embodiments, the isolation film 30 is bonded between the first tab 10 and the second tab 20, for example, when the first tab 10 and the second tab 20 are stacked, the first active material layer 12 is arranged to face the second active material layer 22, and the isolation film 30 is provided with an adhesive layer (not marked in the figure), so that the isolation film 30 can be directly bonded between the first active material layer 12 and the second active material layer 22, thereby improving the integrity of the electrode assembly 100.

[0063] For the above-mentioned first adhesive layer 50, please refer to FIG. 1 and FIG. 2 to FIG. 5, the first adhesive layer 50 is arranged on the surface of the first tab 40 facing the first current collector 11, so as to bond the first empty foil area 113 and the first tab 40, and the surface of the first tab 40 away from the first current collector 11 can be directly in contact with the isolation film 30.

[0064] The first adhesive layer 50 is bonded between the first empty foil area 113 and the first tab 40, so as to bond and fix the first tab 40 and the first current collector 11. Since the first tab 40 is directly bonded and fixed with the first current collector 11 through the first adhesive layer 50, not only the operation is convenient, but also there is no risk of welding burrs and the isolation film 30 being pierced, and there is no need to arrange insulating glue on the first tab 40 or the first empty foil area 113, so that the first tab can be directly in contact with the isolation film, the space occupied by the insulating glue can be saved, and the energy density of the secondary battery can be improved while reducing the cost.

[0065] The first adhesive layer 50 includes at least one of a thermosetting adhesive, a pressure-sensitive adhesive or a hot melt adhesive.

[0066] For example, the first adhesive layer 50 can be a hot melt adhesive. The first adhesive layer 50 can be first bonded to the first empty foil area 113, and then the first tab 40 can be bonded to the first adhesive layer 50 by hot pressing. The hot pressing melts the first adhesive layer 50 and bonds the first adhesive layer 50 between the first empty foil area 113 and the first tab 40. After the first adhesive layer 50 solidifies, the first tab 40 is fixed to the first current collector 11. The first adhesive layer 50 can also be a pressure sensitive adhesive. When the first tab 40, the first adhesive layer 50, and the first current collector 11 are pressure bonded, the first adhesive layer 50 bonds the first current collector 11 and the first tab 40. The first adhesive layer 50 can also be a thermosetting adhesive. After the first adhesive layer 50 is bonded to the first empty foil area 113, the first tab 40 is fixed to the first current collector 11 by hot pressing and solidification.

[0067] The first adhesive layer 50 can be selected from a variety of types. For example, the first adhesive layer 50 includes at least one of an epoxy resin, a polyolefin, a polystyrene, a polymethyl methacrylate, a phenol formaldehyde resin, or a styrene butadiene rubber. For example, the first adhesive layer 50 includes an epoxy resin. The epoxy resin has excellent adhesion and chemical corrosion resistance, strong adhesion after soaking, and small swelling. The epoxy resin can adapt to various electrochemical reactions inside the secondary battery, and the epoxy resin can be cured by heating or reaction with a curing agent to form a strong first adhesive layer 50.

[0068] The first tab 40 is in contact with the first empty foil area 113 through the first adhesive layer 50 to achieve electrical connection between the first tab 40 and the first empty foil area 113. It should be noted that when the first tab 40 is in contact with the first empty foil area 113 through the first adhesive layer 50, the material of the first adhesive layer 50 can be an insulating material or a conductive adhesive. When the first tab 40 does not pass through the first adhesive layer 50, the first adhesive layer 50 is a conductive adhesive.

[0069] For example, in some embodiments, the first adhesive layer 50 has electrical conductivity, and when the first adhesive layer 50 is bonded between the first tab 40 and the first current collector 11, the first tab 40 is electrically connected to the first current collector 11. For example, the first adhesive layer 50 includes a conductive metal filler such as silver, copper, nickel, etc. to make the first adhesive layer 50 conductive, facilitating electrical connection between the first tab 40 and the first current collector 11.

[0070] In some embodiments, referring further to Figures 6 and 7, the surface of the first tab 40 facing the first adhesive layer 50 may also be provided with a plurality of protrusions 42 or a plurality of embedding grooves 41. When the first adhesive layer 50 is bonded between the first tab 40 and the first empty foil area 113, the protrusions 42 can be embedded in the first adhesive layer 50, or the first adhesive layer 50 can be embedded in the embedding grooves 41 of the first tab 40, thereby increasing the frictional force between the first adhesive layer 50 and the first tab 40, increasing the bonding area between the first adhesive layer 50 and the first tab 40, and thus improving the connection strength between the first tab 40 and the first current collector 11. Optionally, the first empty foil area 113 may also be similarly provided with protrusions 42 or embedding grooves 41 to further improve the connection strength between the first tab 40 and the first current collector 11.

[0071] Referring to Figures 1 and 8, when the separator 30 is disposed between the first electrode 10 and the second electrode 20, the first empty foil area 113, the first active material layer 12, and the separator 30 together enclose the first space 14. The first tab 40 is partially disposed in the first space 14, and the first adhesive layer 50 is bonded between the first empty foil area 113 and the first tab 40. The first tab 40 can be first bonded to the first empty foil area 113 using the first adhesive layer 50, and then the separator 30 can be used to cover the first empty foil area 113.

[0072] Since the first tab 40 and the first empty foil area 113 of the first current collector 11 are bonded and fixed by the first adhesive layer 50, no welding socket or welding head is required. Therefore, more third active material layers 13 can be provided on the third surface 112. The single-sided empty foil area can make full use of the internal space of the secondary battery and improve the energy density of the secondary battery. At the same time, neither the first surface 111 nor the third surface 112 will produce welding burrs, which can reduce the risk of the separator 30 being punctured. Furthermore, neither the first surface 111 nor the third surface 112 needs insulating adhesive to cover the burrs, which not only makes full use of space and improves energy density, but also reduces costs.

[0073] Similarly, the second empty foil region 213, the second active material layer 22, and the separator 30 together enclose the second space 24. The second tab 60 is partially disposed in the second space 24, and the second adhesive layer 50 is disposed on the surface of the second tab 60 facing the second current collector 21. The second adhesive layer 70 is bonded between the second empty foil region 213 and the second tab 60. This further reduces the risk of the separator 30 being punctured. Neither the second surface 211 nor the fourth surface 212 requires insulating adhesive to cover burrs, allowing the surface of the second tab 60 facing away from the second current collector 21 to directly contact the separator 30, further improving space utilization and energy density.

[0074] Optionally, referring to Figure 1, an electrode adhesive 80 is disposed along the third direction Z at the position of the first active material layer 12 corresponding to the second empty foil region 213. For example, when viewed along the thickness direction (third direction Z) of the second electrode 20, the projection of the second empty foil region 213 on the first electrode 10 falls onto the electrode adhesive 80, which can alleviate the lithium ion deintercalation of the first electrode 10 at the electrode adhesive 80, so that the second electrode 20 has sufficient margin to intercalate the lithium ions deintercalated from the first electrode 10, thus alleviating lithium plating in the secondary battery. It should be noted that in this embodiment, the first electrode 10 is a positive electrode, and the second electrode 20 is a negative electrode. When the separator 30 is disposed between the first electrode 10 and the second electrode 20, the separator 30 can also cover the electrode adhesive 80.

[0075] Referring to Figure 2, a third space 15 is provided on the surface of the first active material layer 12 facing the second active material layer 22, and the electrode adhesive 80 is at least partially accommodated in the third space 15. The electrode adhesive 80 does not occupy additional thickness space of the first electrode 10, which can improve the energy density of the secondary battery while reducing lithium plating.

[0076] In some embodiments, referring to FIG1, when viewed along the thickness direction (third direction Z) of the first electrode 10, the projection of the first empty foil area 113 on the second electrode 20 is located on the second active material layer 22. Since the first tab 40 is bonded to the first empty foil area 113 through the first adhesive layer 50, there are no welding burrs, and there is no need to provide electrode adhesive 80 on the second active material layer 22 of the second electrode 20, which can further improve space utilization and thus improve the energy density of the secondary battery.

[0077] If the size of the first adhesive layer 50 is too small, it may lead to unstable adhesion with the first current collector 11 or the first tab 40. If the size of the first adhesive layer 50 is too large, it will occupy a large space and is easy to adhere to the first active material layer 12, affecting the capacity and energy density of the secondary battery.

[0078] In the embodiments of this application, referring to Figures 8 and 9, along the width direction (second direction Y) of the first current collector 11, the length of the first empty foil area 113 is L1, and the length of the first adhesive layer 50 is L2, where 0mm ≤ L1 - L2 ≤ 5mm. This facilitates the first tab 40 being disposed in the first empty foil area 113 along the width direction (second direction Y) of the first current collector 11. When L1 - L2 = 0mm, the first adhesive layer 50 can completely bond the first empty foil area 113 along its length, improving the bonding strength. When L1 - L2 ≤ 5mm, the space occupied by the first adhesive layer 50 can be reduced, increasing the energy density of the secondary battery.

[0079] Optionally, there is a gap space between the first adhesive layer 50 and the first active material layer 12, for example, a gap space of less than 5mm is reserved in the width direction (second direction Y) of the first current collector 11 to reduce the direct bonding between the first adhesive layer 50 and the first active material layer 12, thereby reducing the impact of the first adhesive layer 50 on the battery energy density.

[0080] Along the length direction (first direction X) of the first current collector 11, the width of the first empty foil area 113 is W1, and the width of the first adhesive layer 50 is W2, where 0mm ≤ W1 - W2 ≤ 5mm. This facilitates the placement of the first tab 40 in the first empty foil area 113 along the length (first direction X) of the first current collector 11. When W1 - W2 = 0mm, the first adhesive layer 50 can completely bond the first empty foil area 113 along its width, improving the bonding strength. When W1 - W2 ≤ 5mm, the space occupied by the first adhesive layer 50 is reduced, increasing the energy density of the secondary battery.

[0081] Optionally, a gap space of up to 5mm can be reserved in the length direction (first direction X) of the first current collector 11 to reduce the direct bonding between the first adhesive layer 50 and the first active material layer 12, thereby reducing the impact of the first adhesive layer 50 on the energy density of the secondary battery. This not only facilitates the placement of the first tab 40 in the first empty foil area 113, but also facilitates the bonding and fixation of the first tab 40 to the first current collector 11 through the first adhesive layer 50.

[0082] Optionally, along the width direction (second direction Y) of the first current collector 11, the bonding length between the first adhesive layer 50 and the first empty foil area 113 is L3, where 4mm ≤ L3 ≤ 24mm. Along the length direction (first direction X) of the first current collector 11, the bonding width between the first adhesive layer 50 and the first empty foil area 113 is W3, where 4mm ≤ W3 ≤ 14mm. Sufficient bonding length and width increase the bonding area between the first adhesive layer 50 and the first empty foil area 113, improving the connection strength, while reducing the impact of the first adhesive layer 50 on the energy density of the secondary battery. The first adhesive layer 50 is typically bonded integrally to the first empty foil area 113, and the width W2 of the first adhesive layer 50 is the same as the bonding width W3 between the first adhesive layer 50 and the first empty foil area 113, i.e., W2 = W3.

[0083] In some embodiments, along the width direction (second direction Y) of the first electrode 10, the bonding length between the first adhesive layer 50 and the first empty foil region 113 is L3; viewed along the thickness direction (third direction Z) of the first electrode 10, along the width direction of the first electrode 10, the overlap length between the first tab 40 and the first current collector 11 is L4, 50%L4≤L3≤150%L4; and / or, along the length direction (first direction X) of the first electrode 10, the bonding width between the first adhesive layer 50 and the first empty foil region 113 is W3; viewed along the thickness direction of the first electrode 10, along the length direction of the first electrode 10, the overlap width between the first tab 40 and the first current collector 11 is W4, 50%W4≤W3≤150%W4. This improves the connection strength between the first tab 40 and the first current collector 11 while reducing the impact of the first adhesive layer 50 on the energy density of the secondary battery.

[0084] Regarding the thickness of the first adhesive layer 50, if the thickness of the first adhesive layer 50 is too large, it will affect the energy density of the secondary battery; if the thickness of the first adhesive layer 50 is too small, it will easily lead to unstable adhesion between the first tab 40 and the first current collector 11. In the embodiments of this application, along the thickness direction (third direction Z) of the first current collector 11, the thickness of the first adhesive layer 50 is T1, 2μm≤T1≤50μm. When the first current collector 11, the first adhesive layer 50 and the first tab 40 are hot-pressed, the first adhesive layer 50 can stably bond the first tab 40 and the first current collector 11, which can improve the connection strength while reducing the impact of the first adhesive layer 50 on the energy density of the secondary battery.

[0085] Furthermore, 15μm≤T1≤25μm, where 15μm to 25μm is typically the finished thickness of the first adhesive layer 50. During the secondary battery manufacturing process, a high-temperature environment exists, causing the first adhesive layer 50 to rebound. 15μm to 25μm is typically the thickness after the rebound, which can reduce the removal of the tab 40 from the current collector 11.

[0086] Secondly, this application also proposes a secondary battery, including the electrode assembly 100 as described in any embodiment of the first aspect above. The secondary battery may be a lithium-ion battery, a nickel-metal hydride battery, a lead-acid battery, a nickel-cadmium battery, or a lithium iron phosphate battery, etc.

[0087] Experiment 1: [Drop Test of Lithium-ion Batteries]

[0088] Example 1: Preparation of Lithium-ion Batteries

[0089] <Preparation of the positive electrode>

[0090] The positive electrode active material is lithium iron phosphate, the positive electrode conductive agent is acetylene black, and the positive electrode binder is polyvinylidene fluoride (PVDF, with a weight average molecular weight of 5×10⁻⁶). 5The materials were mixed at a mass ratio of 94:3:3, with N-methylpyrrolidone (NMP) added as a solvent. The mixture was stirred under vacuum until a homogeneous positive electrode slurry with a solid content of 75 wt% was obtained. The positive electrode slurry was then uniformly coated onto one surface of a 6 μm thick aluminum foil used as a positive electrode current collector, and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of positive active material (80 μm thick). The above steps were then repeated on the other surface of the aluminum foil, with a first empty foil area of ​​10 mm width and 22 mm length pre-reserved on one surface, resulting in a positive electrode sheet with a double-sided coating of positive active material.

[0091] An epoxy resin first adhesive layer is bonded to the first empty foil area. The bonding width of the first adhesive layer in the first empty foil area is 8 mm, with a 1 mm gap reserved on each side from the positive electrode active material layer. The bonding length is 21 mm, with a 1 mm gap reserved in the length direction from the positive electrode active material layer. The thickness of the first adhesive layer is 20 μm.

[0092] An aluminum sheet is used as the positive electrode tab, which is bonded to the first layer of epoxy resin and fixed to the current collector by hot pressing.

[0093] <Preparation of Negative Electrode Sheets>

[0094] Graphite powder (negative electrode active material), conductive carbon black (Super P) (conductive agent), and styrene-butadiene rubber (SBR) (binder) were mixed in a weight ratio of 97.5:1:1.5. Deionized water was then added as a solvent to prepare a slurry with a solid content of 50 wt%, and the mixture was stirred thoroughly. The slurry was then uniformly coated onto one surface of a 5 μm thick copper foil negative electrode current collector and dried at 110 °C to obtain a negative electrode active material with a weight of 9.1 mg / cm³. 2 Single-sided negative electrode sheet. After completing the above steps, the single-sided coating of the negative electrode sheet is complete. Then, repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a double-sided coating of the negative electrode active material layer. A second empty foil area is reserved on the negative electrode sheet, with a width of 10mm and a length of 22mm. A first epoxy resin adhesive layer is bonded to the first empty foil area. The bonding width of the first adhesive layer in the first empty foil area is 8mm, with a 1mm gap between it and the negative electrode active material layer on each side. The bonding length is 21mm, with a 1mm gap between it and the negative electrode active material layer along its length. The first adhesive layer is embedded in the embedding groove.

[0095] Nickel sheets are used as negative electrode tabs. The negative electrode tabs are bonded to the first layer of epoxy resin and fixed to the current collector by hot pressing.

[0096] <Preparation of the separating membrane>

[0097] A porous polyethylene (PE) film with a thickness of 8 μm was used as the separator.

[0098] <Electrolyte Preparation>

[0099] In a dry argon atmosphere, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a mass ratio of 30:50:20 to obtain an organic solution. Then, lithium hexafluorophosphate is added to the organic solvent to dissolve and mix evenly to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0100] <Preparation of Lithium-ion Batteries>

[0101] The separator, positive electrode, separator, and negative electrode prepared above are stacked in sequence and wound to obtain an electrode assembly. The electrode assembly is then hot-pressed at a pressure of 5 MPa and a temperature of 65°C for 10 seconds. The electrode assembly is placed in an aluminum-plastic film packaging bag, with both the positive and negative electrode tabs extending from the top seal edge of the packaging bag. After removing moisture at 80°C, electrolyte is injected and the bag is sealed.

[0102] In Comparative Example 1, unlike Example 1, the positive electrode tab is welded to the positive current collector, and the negative electrode tab is welded to the negative current collector.

[0103] Drop test method: The lithium-ion batteries were pretreated at 25℃ and allowed to stand at room temperature for 60 minutes. The voltage of the lithium-ion batteries before the drop test was measured. The lithium-ion batteries were then placed in a fixture and dropped freely from a height of 1.5m using a drop device in the following sequence: head-tail-right head corner-right tail corner-left head corner-left tail corner (angle: 45±15°), repeated 6 times. After the drop test, the batteries were allowed to stand at room temperature for 24 hours, and the voltage of the lithium-ion batteries was measured and recorded. The appearance of the lithium-ion batteries was checked and photographed before and after the test. The criteria for passing the drop test were: no smoke, no leakage, and voltage drop <30mV. 100 lithium-ion batteries were tested, and the number of batteries that failed the test was X, resulting in a failure rate of X / 100. The test results are shown in Table 1 below.

[0104] Table 1

[0105] According to Table 1 above, and in conjunction with Example 1 and Comparative Example 1, it can be seen that when the tab and current collector are bonded using a first adhesive layer, the drop test pass rate is significantly better than that of Comparative Example 1. Comparative Example 1 uses welding, and welding burrs can easily puncture the separator. When the lithium-ion battery experiences a drop or other impact, these burrs are more likely to puncture the separator, leading to a short circuit between the positive and negative electrodes and causing the lithium-ion battery to fail. In contrast, Example 1 uses a first adhesive layer, which eliminates welding burrs and effectively reduces the risk of the separator being punctured, thereby improving the impact resistance of the lithium-ion battery.

[0106] Meanwhile, welding is difficult to weld all the overlapping parts of the tab and the current collector, resulting in a small connection area. In contrast, bonding can bond all the overlapping areas of the tab and the current collector. After compression, the first adhesive layer fills the gap between the tab and the current collector, and the embedded groove further increases the connection area between the tab and the current collector, thereby improving the connection strength. The greater the connection strength, the better the tab's resistance to deformation, which can reduce tab tearing and the risk of leakage. It can also reduce the risk of short circuit between the tab and the tab of the other polarity due to bending or skewing, thus reducing the drop failure rate.

[0107] Experiment 2: Energy Density Test and Tensile Strength Test

[0108] Taking the lithium-ion batteries of Example 1 and Comparative Example 1 as examples, their energy density was tested. In Comparative Example 1, the positive electrode used two sheets of insulating adhesive with a thickness of 8 μm and dimensions of 15*30 mm to cover the empty foil areas on both sides of the positive electrode tab, and a positive electrode sheet adhesive with a thickness of 8 μm and dimensions of 15 mm*30 mm to cover the position of the positive electrode active material layer corresponding to the negative electrode tab. The negative electrode used two sheets of insulating adhesive with a thickness of 8 μm and dimensions of 14 mm*28 mm to cover the empty foil areas on both sides of the negative electrode tab, and a negative electrode sheet adhesive with a thickness of 8 μm and dimensions of 15 mm*30 mm to cover the position of the positive electrode active material layer corresponding to the negative electrode tab.

[0109] The relevant parameters in Examples 2 to 9 are shown in Table 2 below.

[0110] Energy density testing method: A square lithium-ion battery was prepared using the above method. The battery was charged to 4.2V with a constant current of 1C, then charged to 0.05C with a constant voltage of 4.2V, and discharged to 2.5V with a constant current of 0.2C. The discharge energy E was recorded. The external dimensions of the square battery were measured, and its volume, V, was calculated. The energy density W = E / V. The test results are shown in Table 2 below.

[0111] Tensile strength test method: Disassemble the battery to obtain the positive electrode and the negative electrode. Taking the positive electrode as an example, use a high-speed rail tensile testing machine to fix the tab to the lower end of the tensile testing machine and fix the current collector to the upper end of the high-speed rail tensile testing machine, keeping both ends on the same vertical plane. Set the speed of the tensile testing machine to 50mm / min, pull the tab and the current collector, and record the tensile force F (in N) when the tab and the current collector are pulled apart.

[0112] Table 2

[0113] Based on Table 2 above, and according to Examples 1 to 9 and Comparative Example 1, it can be seen that when the first adhesive layer is used to bond the tab and the current collector, the tensile strength is significantly higher than that of Comparative Example 1. This is because welding is difficult to weld all the overlapping parts of the tab and the current collector, resulting in a smaller connection area. However, bonding can bond all the overlapping areas of the tab and the current collector. After pressing, the first adhesive layer fills the gap between the tab and the current collector, and the setting of the embedding groove makes the connection area between the tab and the current collector larger, thereby improving the connection strength.

[0114] In Examples 1 and 3 to 9, the tensile strength is superior to that in Example 2. In Examples 1 and 3 to 9, the width of the first adhesive layer is greater than 4 mm, which increases the connection area between the tab and the current collector, thus improving the connection strength of the tab. In Examples 1 and 3 to 8, the energy density is higher than that in Example 9. This may be because the width of the first adhesive layer is too large, which easily leads to the first adhesive layer directly adhering to the active material layer, affecting the battery capacity. Furthermore, in Examples 8 and 9, the width of the first adhesive layer does not significantly improve the tensile strength. This may be because part of the first adhesive layer adheres to the active material layer, resulting in poor adhesion in that part. Therefore, in this application, the width of the first adhesive layer is selected as 4 mm ≤ W2 ≤ 14 mm, that is, the adhesion width between the first adhesive layer and the first empty foil area is 4 mm ≤ W3 ≤ 14 mm.

[0115] Furthermore, in Examples 1 and 3 to 6, the energy density is not only higher than that in Examples 7 to 9, but the tensile strength is also higher than that in Example 2. In Examples 7 to 9, as the width of the first adhesive layer increases, the effect on improving the tensile strength becomes less and less significant, because the width of the first adhesive layer is greater than the width of the first empty foil area, and part of the first adhesive layer is directly bonded to the active material layer. The portion bonded to the active material layer has a smaller effect on improving the connection strength. In Examples 1 and 3 to 6, the width of the first adhesive layer is less than or equal to the width of the first empty foil area, which reduces the direct bonding with the active material layer, and the sufficient width can improve the connection strength, with a smaller impact on the energy density.

[0116] In Example 3, both tensile strength and energy density are high. In Example 6, the width of the first empty foil area is the same as the width of the first adhesive layer, which allows the first adhesive layer to completely bond the first empty foil area in the width direction, improving the bonding strength. However, in Examples 7 to 9, the width of the first adhesive layer is too large. Although it can completely bond the first empty foil area in the width direction, it has a significant impact on the energy density. Therefore, in this application, the width difference between the first empty foil area and the first adhesive layer is selected to be 0mm ≤ W1 - W2 ≤ 5mm. Based on the same inventive concept, the width difference in the length direction of the first adhesive layer can also be selected to be 0 to 5mm. From Examples 6-9, when W2 ≥ W1, the tensile strength remains basically unchanged, while the energy density decreases as W2 increases.

[0117] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. An electrode assembly, comprising a first electrode, a separator, and a second electrode, wherein the separator is disposed between the first electrode and the second electrode; the first electrode comprises a first current collector and a first active material layer, the first current collector having a first surface facing the second electrode, and the first active material layer being disposed on the first surface; the second electrode comprises a second current collector and a second active material layer, the second current collector having a second surface facing the first active material layer, and the second active material layer being disposed on the second surface; characterized in that, The electrode assembly further includes a first tab and a first adhesive layer; The first surface has a first empty foil area, the first empty foil area, the first active material layer and the separator membrane together enclose a first space, the first electrode tab is disposed in the first space, and the first adhesive layer is disposed on the surface of the first electrode tab facing the first current collector to bond the first empty foil area and the first electrode tab, the first empty foil area is electrically connected to the first electrode tab, and the surface of the first electrode tab away from the first current collector is in contact with the separator membrane.

2. The electrode assembly according to claim 1, characterized in that, The electrode assembly further includes a second tab and a second adhesive layer. The second surface has a second empty foil area. The second empty foil area, the second active material layer, and the separator membrane together form a second space. The second tab is partially disposed in the second space, and the second adhesive layer is disposed on the surface of the second tab facing the second current collector to bond the second empty foil area to the second tab. The surface of the second tab away from the second current collector is in contact with the separator membrane.

3. The electrode assembly according to claim 1, characterized in that, When viewed along the thickness direction of the first electrode, the projection of the first empty foil area onto the second electrode is located in the second active material layer.

4. The electrode assembly according to claim 2, characterized in that, An electrode adhesive is disposed on the surface of the first active material layer facing the second active material layer; When viewed along the thickness direction of the second electrode, the projection of the second empty foil area onto the first electrode lies within the projection of the electrode adhesive; The first electrode is the positive electrode, and the second electrode is the negative electrode.

5. The electrode assembly according to claim 1, characterized in that, A third space is provided on the surface of the first active material layer facing the second active material layer, and the electrode adhesive is at least partially contained in the third space.

6. The electrode assembly according to claim 1, characterized in that, The first current collector also has a third surface, and the first surface and the third surface are disposed opposite to each other along the thickness direction of the first current collector; The first electrode also has a third active material layer, which is disposed on the third surface. When viewed along the thickness direction of the first electrode, the projection of the first empty foil area falls on the projection of the third active material.

7. The electrode assembly according to claim 1, characterized in that, Along the width direction of the first electrode sheet, the length of the first empty foil area is L1, the length of the first adhesive layer is L2, and 0mm ≤ L1 - L2 ≤ 5mm; and / or, Along the length of the first electrode, the width of the first empty foil area is W1, and the width of the first adhesive layer is W2, where 0mm ≤ W1 - W2 ≤ 5mm.

8. The electrode assembly according to claim 1, characterized in that, Along the width direction of the first electrode sheet, the bonding length between the first adhesive layer and the first empty foil area is L3, 4mm≤L3≤24mm; Along the length of the first electrode, the bonding width between the first adhesive layer and the first empty foil area is W3, 4mm≤W3≤14mm; Along the thickness direction of the first electrode, the thickness of the first adhesive layer is T1, where 2μm≤T1≤50μm.

9. The electrode assembly according to claim 1, characterized in that, Along the width direction of the first electrode sheet, the bonding length between the first adhesive layer and the first empty foil area is L3; viewed along the thickness direction of the first electrode sheet, along the width direction of the first electrode sheet, the overlap length between the first electrode tab and the first current collector is L4, where 50%L4≤L3≤150%L4; and / or, Along the length of the first electrode, the bonding width between the first adhesive layer and the first empty foil area is W3; when viewed along the thickness direction of the first electrode, along the length of the first electrode, the overlap width between the first electrode tab and the first current collector is W4, where 50%W4≤W3≤150%W4.

10. The electrode assembly according to claim 7, characterized in that, Along the length direction of the first current collector, there is a gap space between the first adhesive layer and the first active material layer; And / or, Along the width direction of the first current collector, there is a gap space between the first adhesive layer and the first active material layer.

11. The electrode assembly according to claim 1, characterized in that, The first adhesive layer includes at least one of epoxy resin, polyolefin, polystyrene, polymethyl methacrylate, phenolic resin or styrene-butadiene rubber.

12. The electrode assembly according to claim 1, characterized in that, The first adhesive layer includes at least one of hot melt adhesive, pressure-sensitive adhesive, or thermosetting adhesive, and a portion of the first tab passes through the first adhesive layer and contacts the first empty foil area.

13. The electrode assembly according to claim 1, characterized in that, The first adhesive layer is a conductive adhesive layer.

14. A secondary battery, characterized in that, Includes the electrode assembly as described in any one of claims 1 to 13.

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