Electrode sheet and secondary battery

Abstract

An electrode sheet (10) and a secondary battery. The electrode sheet comprises a current collector (11), a first insulating layer (12), a second insulating layer (13), a first adapter portion (14a) and a second adapter portion (14b), wherein the current collector (11) comprises a first metal layer (112), a polymer layer (111) and a second metal layer (113), which are sequentially arranged, the first metal layer (112) having a first surface (1121) facing away from the polymer layer (111), the second metal layer (113) having a second surface (1131) facing away from the polymer layer (111), and in the widthwise direction of the current collector (11), the current collector (11) comprising a coating section (11a) and an empty foil section (11b), which are connected to each other; the first insulating layer (12) is arranged on the coating section (11a) on the first surface (1121) and extends to the empty foil section (11b); the second insulating layer (13) is arranged on the coating section (11a) on the second surface (1131) and extends to the empty foil section (11b); the first adapter portion (14a) is electrically connected to the current collector (11) on the first surface (1121) of the empty foil section (11b), the distance between the first adapter portion (14a) and the first insulating layer (12) is L1 mm, and 0 mm≤L1≤1 mm; and the second adapter portion (14b) is electrically connected to the current collector (11) on the second surface (1131) of the empty foil section (11b), the distance between the second adapter portion (14b) and the second insulating layer (13) is L2 mm, and 0 mm≤L2≤1 mm. The piercing of an isolation film (20) by burrs of a metal layer can be reduced, thereby decreasing the risk of a short circuit of a battery.

Description

Electrode and secondary battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on January 8, 2024, with application number 202410027115.3 and invention name “Pole and Secondary Battery”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The embodiments of the present application relate to the field of electrochemical technology, and in particular to a pole piece and a secondary battery. Background Art

[0004] With the continuous advancement and development of battery technology, the application areas of batteries are also expanding, and the resulting battery safety issues are gaining increasing public attention. Frequent safety incidents, such as thermal runaway after mechanical damage, have created certain obstacles to battery development. Addressing battery safety issues is a current challenge. Conventional battery safety protection methods generally aim to delay thermal runaway, but struggle to address safety issues caused by mechanical damage, resulting in significant limitations in their application.

[0005] A composite current collector (Metal polymer film, MPF) comprises a metal layer-polymer layer-metal layer composite structure. Using polymers as the mechanical performance process backbone for the current collector can reduce the thickness of the metal layer, resulting in a certain weight reduction and improving the battery's gravimetric energy density. However, during battery manufacturing, the polymer material and the tabs struggle to form a co-integrated bond. After welding the tabs to the current collector, cold welds or over-welding can occur, affecting the battery's overall electrical performance and welding reliability. Furthermore, burrs on the current collector can easily pierce the battery's separator, causing contact between the positive and negative electrodes and resulting in a short circuit. Summary of the Invention

[0006] The embodiments of the present application aim to provide a pole piece and a secondary battery, which can reduce the risk of current collector burrs piercing the isolation membrane, thereby reducing the occurrence of battery short circuits.

[0007] In order to solve the technical problems, the embodiments of the present application adopt the following technical solutions:

[0008] In the first aspect, the present application proposes a pole piece, comprising a current collector, a first insulating layer, a second insulating layer, a first transition portion, and a second transition portion. Along the thickness direction of the current collector, the current collector comprises a first metal layer, a polymer layer, and a second metal layer arranged in sequence, the first metal layer having a first surface facing away from the polymer layer, and the second metal layer having a second surface facing away from the polymer layer; along the width direction of the current collector, the current collector comprises a connected coating segment and a hollow foil segment. The first insulating layer is arranged on one side of the first surface of the first metal layer, a portion of the first insulating layer is arranged in the coating segment, and the other portion is arranged in the hollow foil segment. The first transition portion is electrically connected to the current collector at the first surface of the hollow foil segment, and the distance between the first transition portion and the first insulating layer is L1mm, 0mm≤L1≤1mm.

[0009] In the above technical solution, by setting the first adapter to be electrically connected to the first metal layer, the first insulating layer partially covers the empty foil segment, which can improve the strength of the empty foil segment, reduce the deformation and tearing of the empty foil segment, and improve the ability of the electrode to resist mechanical damage. The distance between the first adapter and the first insulating layer is limited to L1mm, 0mm≤L1≤1mm, which can effectively reduce the risk of burrs piercing the isolation membrane close to the first metal layer, thereby reducing the risk of battery short circuit.

[0010] In some preferred embodiments, the pole piece also includes a second insulating layer, which is arranged on one side of the second surface of the second metal layer, a portion of the second insulating layer is arranged in the coating section, and the other portion is arranged in the empty foil section, and the second transition portion is electrically connected to the current collector on the second surface of the empty foil section, and the distance between the second transition portion and the second insulating layer is L2mm, 0mm≤L2≤1mm.

[0011] In the above technical solution, by providing a first transition portion and a second transition portion, the first transition portion is electrically connected to the first metal layer of the current collector, and the second transition portion is electrically connected to the second metal layer of the current collector. This double-sided electrical connection improves the reliability of the electrical connection between the two transition portions and the current collector, alleviating the problem of the difficulty in symbiotic bonding between the polymer material and the transition portion. Furthermore, limiting the distance between the second transition portion and the second insulating layer to L2mm, with 0mm≤L2≤1mm, further reduces the risk of burrs piercing the separator, thereby reducing the risk of battery short circuits.

[0012] In some preferred embodiments, 0 mm ≤ L1 ≤ 0.5 mm, and 0 mm ≤ L2 ≤ 0.5 mm, further ensuring that the first insulating layer and the second insulating layer cover the burrs of the empty foil segment, thereby reducing the risk of burrs piercing the isolation film.

[0013] In some preferred embodiments, the electrode further includes at least two welding portions, each electrically connected to the first transition portion and the second transition portion, ensuring good contact between the first transition portion and the second transition portion, thereby achieving double-sided electrical connection. Furthermore, at least one welding portion is electrically connected to the current collector to improve current carrying capacity.

[0014] In some preferred embodiments, along the width direction of the current collector, the distance between the welding portion and the first insulating layer or the second insulating layer is L3mm, 0mm≤L3≤1mm, L3>L1, L3>L2, and the defined welding portion is on the two transition portions to ensure welding reliability.

[0015] In some preferred embodiments, a first coating layer is provided on the first surface of the coated segment, a first insulating layer is bonded to the first coating layer and the first surface of the hollow foil segment, and a first active material layer is provided on the surface of the first coating layer facing away from the coated segment. This effectively protects the first metal layer of the current collector from being punctured by sharp particles of the first active material layer, thereby ensuring the integrity of the current collector's conductive network. A second coating layer is provided on the second surface of the coated segment, a second insulating layer is bonded to the second coating layer and the second surface of the hollow foil segment, and a second active material layer is provided on the surface of the second coating layer facing away from the coated segment. This effectively protects the second metal layer of the current collector from being punctured by sharp particles of the second active material layer, thereby ensuring the integrity of the current collector's conductive network.

[0016] In some preferred embodiments, the first coating layer has a first section disposed near the empty foil segment, the first section is not provided with the first active material layer, and the length of the first section along the width direction of the current collector is L4mm, 1mm≤L4≤1.8mm, thereby reducing the portion of the current collector not provided with the active material layer from piercing the isolation membrane near the first metal layer, thereby reducing the occurrence of short circuits. The second coating layer has a second section disposed near the empty foil segment, the second section is not provided with the second active material layer, and the length of the second section along the width direction of the current collector is L5mm, 1mm≤L5≤1.8mm. ， The portion of the current collector where the active material layer is not provided is reduced from piercing the separator close to the second metal layer.

[0017] In some preferred embodiments, the first coating and / or the second coating include an inorganic ceramic, an insulating organic polymer, and conductive particles. The inorganic ceramic includes at least one of aluminum oxide, boehmite, silicon dioxide, calcite, magnesite, barium sulfate, lead sulfate, calcium sulfate, or copper sulfate. The insulating organic polymer includes at least one of polyethylene, polypropylene, polybutene, polypentene, polyhexene, polyvinyl alcohol, polyacrylamide, polyester fiber, polyvinyl alcohol-polyester, polyethylene glycol ester, polycaprolactone, polybutylene succinate, polyether ester, polycarbonate, or rubber. The conductive particles include carbon black, graphene, or acetylene black.

[0018] In some preferred embodiments, along the thickness direction of the current collector, the thickness of the current collector is T1μm, 4μm≤T1≤20μm; optionally, the thickness of the first coating is T2μm, 0.5μm≤T2≤4μm; it can effectively protect the first metal layer of the current collector from being punctured by the sharp particles of the first active material layer, thereby ensuring the integrity of the conductive network of the current collector. Optionally, the thickness of the second coating is T3μm, 0.5μm≤T3≤4μm; it can effectively protect the second metal layer of the current collector from being punctured by the sharp particles of the second active material layer, thereby ensuring the integrity of the conductive network of the current collector. Optionally, the thickness of the first transition portion is T4μm, 8μm≤T4≤15μm; optionally, the thickness of the second transition portion is T5μm, 6μm≤T5≤10μm ， Limiting the thickness range can ensure the strength of the first transition portion. For example, when the first transition portion is welded to the empty foil segment, the welding strength can be ensured, the welding stability can be improved, and the resistance can be reduced, which can improve the current carrying capacity of the first transition portion.

[0019] In some preferred embodiments, the thickness of the welding portion along the thickness direction of the current collector is T6 μm, 20 μm≤T6≤50 μm; the strength of the welding portion is ensured to stably connect the first transition portion and the second transition portion, ensuring good contact between the first transition portion and the second transition portion.

[0020] Optionally, along the width direction of the current collector, the width of the empty foil segment is W1mm, 1mm≤W1≤5mm; while reducing the risk of burrs piercing the isolation membrane, sufficient connection area is reserved to facilitate the fixation of the first transition portion and the empty foil segment.

[0021] Optionally, along the width direction of the current collector, the width of a single welding portion is W2mm, 1mm≤W2≤3mm; this ensures good contact between the first transition portion and the second transition portion, improves electrical connection stability, and improves current carrying capacity.

[0022] In some preferred embodiments, the electrode further comprises a first adhesive layer and a second adhesive layer. The first adhesive layer is disposed on the surface of the first transition portion facing away from the second transition portion. The first adhesive layer can partially cover burrs on the first transition portion, thereby reducing the risk of burrs penetrating the isolation membrane near the first metal layer. Observed from the direction from the first adhesive layer to the first transition portion, the first adhesive layer covers the weld portion; the first adhesive layer protects the weld area between the weld portion and the first transition portion, ensuring insulation of this area. Furthermore, the first adhesive layer covers partially burrs on the weld portion, further reducing the risk of burrs penetrating the isolation membrane near the first metal layer.

[0023] The second adhesive layer is set on the surface of the second transition part away from the first transition part. The second adhesive layer can cover part of the burrs of the second transition part to reduce the burrs from penetrating the isolation film near the second metal layer. ；The second adhesive layer can protect the welding area between the welding part and the second transition part to ensure insulation of the area, and the second adhesive layer covers part of the burrs of the welding part, which can further reduce the burrs from piercing the isolation film close to the second metal layer.

[0024] In some preferred embodiments, the first adhesive layer is bonded to the first insulating layer, and the second adhesive layer is bonded to the second insulating layer, so that the first metal layer and the second metal layer exposed in the empty foil segment are completely insulated and isolated, which not only reduces the occurrence of short circuits but also improves the tear resistance of the empty foil segment.

[0025] In some preferred embodiments, along the width direction of the current collector, the width of the first adhesive layer is W3mm, 1.2mm≤W3≤5mm, ensuring that the first adhesive layer covers the welding portion while facilitating adhesion to the first insulating layer.

[0026] Optionally, along the width direction of the current collector, the width of the second adhesive layer is W4mm, 1.2mm≤W4≤5mm; while ensuring that the second adhesive layer covers the welding portion, it is convenient to bond with the second insulating layer.

[0027] Optionally, along the thickness direction of the current collector, the thickness of the first adhesive layer is T7μm, 5μm≤T7≤40μm; this can reduce the risk of burrs piercing the first adhesive layer while ensuring stable bonding, and can minimize the space occupied by the first adhesive layer, thereby improving the volume energy density of the battery.

[0028] Optionally, along the thickness direction of the current collector, the thickness of the second glue layer is T8 μm, 5 μm ≤ T8 ≤ 30 μm ； While stably covering the burrs, it ensures stable bonding and can minimize the space occupied by the first adhesive layer, thereby increasing the volume energy density of the battery.

[0029] In some preferred embodiments, the first adhesive layer and / or the second adhesive layer includes polyolefin hot melt adhesive. Polyolefin hot melt adhesive is resistant to electrolyte corrosion and can improve the service life of the battery and the bonding reliability.

[0030] In some preferred embodiments, along the thickness direction of the current collector, the thickness of the first insulating layer is T9 μm, 15 μm ≤ T9 ≤ 40 μm, so as to fully isolate some burrs of the first metal layer. The thickness of the second insulating layer is T 10 μm, 15μm≤T 10 The thickness of the first insulating layer is ≤40μm to fully isolate some burrs on the second metal layer. Along the width of the current collector, the width of the first insulating layer is W5mm, 1.5mm≤W5≤4mm, ensuring insulation of the empty foil segments and reducing internal short circuits in the battery. The width of the second insulating layer is W6mm, 1.5mm≤W6≤4mm, further reducing internal short circuits in the battery.

[0031] In some preferred embodiments, 0.1 mm ≤ W5-W6 ≤ 0.5 mm ， Ensure the consistency of both sides of the current collector in the thickness direction and reduce the pressure damage of the first insulating layer and the second insulating layer to the current collector during cold pressing.

[0032] In a second aspect, the present application further proposes a secondary battery comprising a pole piece as described in any embodiment of the first aspect above. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] One or more embodiments are exemplarily illustrated by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are represented as similar elements, and unless otherwise stated, the figures in the drawings do not constitute proportional limitations.

[0034] FIG1 is a schematic diagram of the winding structure of an electrode assembly according to some embodiments of the present application;

[0035] FIG2 is a schematic diagram of the stacked structure of an electrode assembly according to some embodiments of the present application;

[0036] FIG3 is a schematic diagram of the structure of a pole piece in some embodiments of the present application;

[0037] FIG4 is a schematic structural diagram of a current collector in some embodiments of the present application;

[0038] FIG5 is a partial enlarged view of point A in FIG3 ;

[0039] FIG6 is a schematic structural diagram of a pole piece in some embodiments of the present application;

[0040] FIG7 is a schematic structural diagram of a pole piece in some embodiments of the present application;

[0041] FIG8 is a schematic structural diagram of a pole piece in some embodiments of the present application;

[0042] FIG9 is a partial enlarged view of point B in FIG8 ;

[0043] FIG10 is a schematic structural diagram of a pole piece in some embodiments of the present application;

[0044] FIG11 is a schematic diagram of the structure of the pole piece of some embodiments of the present application.

[0045] Explanation of the accompanying drawings: 100, electrode assembly; 10a, positive electrode sheet; 10b, negative electrode sheet; 20, separator; 10, electrode sheet; 11, current collector; 11a, coating section; 11b, hollow foil section; 111, polymer layer; 112, first metal layer; 1121, first surface; 113, second metal layer; 1131, second surface; 12, first insulating layer; 13, second insulating layer; 14a, first transition portion; 14b, second transition portion; 15a, first active material layer; 15b, second active material layer; 16, welding portion; 17a, first coating layer; 17a1, first section; 17b, second coating layer; 17b1, second section; 18a, first adhesive layer; 18b, second adhesive layer; X, first direction; Y, second direction. DETAILED DESCRIPTION

[0046] The following embodiments of the technical solution of the present application will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application and are therefore only examples and are not intended to limit the scope of protection of the present application.

[0047] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0048] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0049] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive with other embodiments. Furthermore, the technical features described below in the different embodiments of the present application may be combined with each other as long as they do not conflict with each other.

[0050] On the first aspect, an embodiment of the present application proposes a pole piece 10, which is an important component inside the battery. For example, the pole piece 10 is divided into a positive pole piece 10a and a negative pole piece 10b. Please refer to Figure 1. An isolation film 20 is arranged between the positive pole piece 10a and the negative pole piece 10b. After the positive pole piece 10a, the isolation film 20 and the negative pole piece 10b are stacked, they are wound to form an electrode assembly 100. The electrode assembly 100 is housed in a shell (not shown in the figure) and liquid-filled and sealed to form a battery; or, please refer to Figure 2, the positive pole piece 10a and the negative pole piece 10b are alternately stacked in sequence, and an isolation film 20 is arranged between adjacent positive pole pieces 10a and negative pole pieces 10b to form an electrode assembly 100. The electrode assembly 100 is housed in a shell and liquid-filled and sealed to form a battery. In the embodiment of the present application, the electrode 10 is taken as a positive electrode 10a as an example. Referring to FIG3 , the electrode 10 includes a current collector 11, a first insulating layer 12, a second insulating layer 13, a first transition portion 14a, and a second transition portion 14b. In other embodiments, the electrode 10 may also be a negative electrode 10b.

[0051] Regarding the above-mentioned current collector 11, the current collector 11 is a component used to collect and transmit the current generated inside the battery, and it is usually made of a conductive material, such as copper, aluminum or nickel. In the embodiment of the present application, a composite current collector 11 can be used. Please refer to Figures 3 and 4. Along the thickness direction of the current collector 11 (the second direction Y), the current collector 11 includes a first metal layer 112, a polymer layer 111 and a second metal layer 113 stacked in sequence. Among them, the thickness of the current collector 11 can be set to T1μm, 4≤T1≤20, reducing the space occupied by the current collector 11, which can facilitate the improvement of the volume energy density of the battery. At the same time, sufficient thickness can increase the strength of the current collector 11, so as to facilitate the processing and molding of the current collector 11.

[0052] The polymer layer 111 is located between the first metal layer 112 and the second metal layer 113. The polymer layer 111 serves as the mechanical performance process skeleton of the current collector 11. The first metal layer 112 and the second metal layer 113 can be appropriately thinned, resulting in a certain weight reduction, which can improve the weight energy density of the battery. At the same time, the thinning of the metal layer reduces the metal burrs generated when the battery is mechanically damaged, which can reduce the burrs from piercing the isolation membrane 20, thereby reducing the risk of internal short circuit failure of the battery. Since the deformation ability and ductility of polymers are better than those of metals, the composite current collector 11 has better collision resistance and has a wider operating space in processing. Therefore, the composite current collector 11 can take into account multiple advantages such as weight reduction, increased energy density, and safe mechanical processing of batteries. The polymer layer 111 can be made of a lightweight and thin polymer film. For example, the material of the polymer layer 111 is selected from one or more of polyethylene terephthalate, polyethylene, polypropylene, polyamide, polyimide, polyvinyl chloride or polystyrene. The use of the polymer layer 111 made of the above materials can reduce the overall weight of the composite current collector 11 and improve the weight energy density of the battery.

[0053] The first metal layer 112 can be deposited on the surface of the polymer layer 111 by vacuum evaporation, vacuum coating, electroplating, or magnetron sputtering. To facilitate the deposition of the first metal layer 112, the first metal layer 112 can be made of aluminum or an aluminum alloy with a relatively low boiling point. For example, the aluminum or aluminum alloy can be heated in a vacuum, vaporized, and deposited on the surface of the polymer layer 111, thereby imparting electrical conductivity to the surface of the polymer layer 111. The second metal layer 113 can also be deposited on the other surface of the polymer layer 111 using a similar method.

[0054] The first metal layer 112 has a first surface 1121 facing away from the polymer layer 111. The first active material layer 15a can be disposed on the first surface 1121. The coating weight of the first active material layer 15a can be selected from (100 to 400 mg) / 1540.25 mm 2, to ensure a higher energy density of the battery. Similarly, the second metal layer 113 has a second surface 1131 away from the polymer layer 111, and the second active material layer 15b can be provided on the second surface 1131. Exemplarily, along the width direction of the current collector 11 (the first direction X), the current collector 11 includes a connected coating segment 11a and an empty foil segment 11b (the coating segment 11a and the empty foil segment 11b are separated by a dotted line G in the figure), the first active material layer 15a can be provided on the coating segment 11a of the first surface 1121, the second active material layer 15b can be provided on the coating segment 11a of the second surface 1131, and the empty foil segment 11b is the portion of the current collector 11 where no active material layer is provided, the empty foil segment 11b of the first surface 1121 exposes the first metal layer 112, which can be used to electrically connect to the above-mentioned first transition portion 14a, and the empty foil segment 11b of the second surface 1131 exposes the second metal layer 113, which can be used to electrically connect to the above-mentioned second transition portion 14b.

[0055] Regarding the above-mentioned first insulating layer 12, please refer to Figures 3 and 5. The first insulating layer 12 is arranged on one side of the first surface 1121 of the first metal layer 112. A portion of the first insulating layer 12 is arranged on the coated segment 11a and another portion is arranged on the empty foil segment 11b. For example, the first insulating layer 12 can be bonded to a portion of the first active material layer 15a and the empty foil segment 11b (see Figure 6), or the first insulating layer 12 can be bonded only to the empty foil segment 11b (see Figure 3). The first insulating layer 12 partially covers the empty foil segment 11b, which can increase the strength of the empty foil segment 11b and reduce deformation and tearing of the empty foil segment 11b. In addition, the first insulating layer 12 can cover some burrs of the first metal layer 112. When the electrode 10 is assembled into a battery, it can reduce the burrs from piercing the isolation membrane near the first metal layer 112, thereby reducing battery short circuits. The thickness of the first insulating layer 12 along the thickness direction of the current collector 11 (the second direction Y) is T9 μm, with 15 μm ≤ T9 ≤ 40 μm, to fully isolate some burrs on the first metal layer 112. The first insulating layer 12 can be made of a polyolefin hot melt adhesive, which is resistant to electrolyte corrosion and can reduce corrosion damage to the first insulating layer 12, thereby increasing the life of the electrode 10 or the battery. In other embodiments, the first insulating layer 12 can also be made of an insulating tape such as a pressure-sensitive adhesive.

[0056] For the above-mentioned second insulating layer 13, please refer to Figures 3 and 5. The second insulating layer 13 is arranged on one side of the second surface 1131 of the second metal layer 113. A part of the second insulating layer 13 is arranged on the coating segment 11a, and the other part is arranged on the empty foil segment 11b. For example, the second insulating layer 13 can be bonded to part of the second active material layer 15b and the empty foil segment 11b, or the second insulating layer 12 is only bonded to the empty foil segment 311b, which can further improve the strength of the empty foil segment 11b and reduce the deformation and tearing of the empty foil segment 11b. In addition, the second insulating layer 13 covers part of the burrs of the second metal layer 113, which can reduce the burrs piercing the isolation film 20 near the second metal layer 113, thereby reducing battery short circuits. Among them, along the thickness direction of the current collector 11 (the second direction Y), the thickness of the second insulating layer 13 is T 10 μm, 15μm≤T 10 ≤40μm to fully isolate some burrs of the second metal layer 113. Similar to the first insulating layer 12, the second insulating layer 13 can also be made of polyolefin hot melt adhesive to reduce corrosion damage to the second insulating layer 13. Similarly, the second insulating layer 13 can also be made of insulating tape such as pressure sensitive adhesive.

[0057] Optionally, along the width direction of the current collector 11 (first direction X), the width of the first insulating layer 12 is W5mm, 1.5mm≤W5≤4mm, to ensure the insulation of the empty foil segment 11b and reduce internal short circuits in the battery. Similarly, the width of the second insulating layer 13 is W6mm, 1.5mm≤W6≤4mm. Preferably, 0.1mm≤W5-W6≤0.5mm. For example, when observed along the thickness direction of the current collector 11 (second direction Y), the misalignment size of the first insulating layer 12 and the second insulating layer 13 is 0.1~0.5mm, to ensure the consistency of the two sides of the current collector 11 in the thickness direction, and to reduce the pressure damage of the first insulating layer 12 and the second insulating layer 13 to the current collector 11 during cold pressing.

[0058] Regarding the first transition portion 14a, please refer to FIG6 . The first transition portion 14a is electrically connected to the current collector 11 on the first surface 1121 of the hollow foil segment 11b, for example, by welding or conductive adhesive bonding. The material of the first transition portion 14a can be a conductive material such as aluminum, aluminum alloy, copper, or nickel. The first transition portion 14a can be connected to an external circuit for charging and discharging. The distance between the first transition portion 14a and the first insulating layer 12 is L1mm, 0mm≤L1≤1mm. The first insulating layer 12 covers the burrs of the hollow foil segment 11b, reducing the risk of burrs piercing the isolation membrane 20 in the battery. In the embodiment of the present application, the distance between the first transition portion 14a and the first insulating layer 12 is limited to L1mm, which can effectively reduce the risk of burrs piercing the isolation membrane, thereby reducing the risk of battery short circuits. To facilitate electrical connection between first transition portion 14a and hollow foil segment 11b, the width of hollow foil segment 11b along the width direction of current collector 11 (first direction X) is W1mm, with 1mm≤W1≤5mm. This reduces the risk of burrs piercing the separator while leaving sufficient connection area for securing first transition portion 14a to hollow foil segment 11b. Furthermore, 0≤L1≤0.5 further ensures that first insulating layer 12 covers burrs on hollow foil segment 11b, reducing the risk of burrs piercing the separator.

[0059] Optionally, along the thickness direction of the current collector 11 (the second direction Y), the thickness of the first transition portion 14a is T4 μm, 8 μm ≤ T4 ≤ 15 μm. Limiting this thickness range can ensure the strength of the first transition portion 14a. For example, when the first transition portion 14a is welded to the empty foil segment 11b, the welding strength can be guaranteed, the welding stability can be improved, and its resistance is smaller, which can improve the current carrying capacity of the first transition portion 14a.

[0060] Regarding the second transition portion 14b, please refer to Figure 6. The second transition portion 14b is electrically connected to the second surface 1131 of the empty foil segment 11b and the current collector 11. Similar to the first transition portion 14a, the second transition portion 14b can also be made of conductive materials such as aluminum, aluminum alloy, copper or nickel. The first transition portion 14a and the second transition portion 14b can be simultaneously connected to the external circuit. The provision of two transition portions can improve the current carrying capacity and facilitate high-rate charging and discharging. The distance between the second transition portion 14b and the second insulating layer 13 is L2mm, 0mm≤L2≤1mm. Limiting the distance between the second transition portion 14b and the second insulating layer 13 to L2mm can further reduce the risk of burrs piercing the isolation membrane, thereby reducing the risk of battery short circuits. Furthermore, 0≤L2≤0.5. Optionally, along the thickness direction of the current collector 11 (second direction Y), the thickness of the second transition portion 14b is T5μm, 6μm≤T5≤10μm, which improves the strength of the second transition portion 14b while improving the current carrying capacity of the second transition portion 14b.

[0061] Referring to FIG. 7 , in some embodiments, the electrode 10 further includes at least two welding portions 16 , each electrically connected to the first transition portion 14 a and the second transition portion 14 b . At least one welding portion 16 is electrically connected to the current collector 11 . The welding portion 16 can be made of an aluminum bar, a copper bar, or a nickel bar. One end of the welding portion 16 can be welded to the first transition portion 14 a and the other end to the second transition portion 14 b via roller welding. This ensures good contact between the first and second transition portions 14 a and 14 b , achieving a double-sided electrical connection. Furthermore, at least one welding portion 16 is electrically connected to the current collector 11 to improve current carrying capacity. Along the thickness direction (second direction Y) of the current collector 11 , the thickness of the welding portion 16 is T6 μm, with a range of 20 μm ≤ T6 ≤ 50 μm. This ensures the strength of the welding portion 16 , ensuring stable connection between the first and second transition portions 14 a and 14 b , and ensuring good contact between the first and second transition portions 14 a and 14 b . Along the width direction of the current collector 11 (first direction X), the width of a single welding portion 16 is W2 mm, 1 mm ≤ W2 ≤ 3 mm, ensuring good contact between the first transition portion 14 a and the second transition portion 14 b , improving electrical connection stability, and increasing current carrying capacity.

[0062] Preferably, the distance between the welding portion 16 and the first insulating layer 12 and / or the second insulating layer 13 is limited to L3mm, 0mm≤L3≤1mm, to reduce the burrs of the empty foil segment 11b from piercing the isolation membrane 20, wherein L3>L1, L3>L2, and the limited welding portion 16 is on the two transition portions to ensure welding reliability.

[0063] Referring to Figures 8 and 9, in some embodiments, the first surface 1121 of the coating segment 11a is further provided with a first coating layer 17a. The first active material layer 15a can be provided on a surface of the first coating layer 17a facing away from the coating segment 11a. The thickness of the first coating layer 17a along the thickness direction (second direction Y) of the current collector 11 can be set to T2 μm, with 0.5 μm ≤ T2 ≤ 4 μm. This effectively protects the first metal layer 112 of the current collector 11 from being punctured by sharp particles of the first active material layer 15a, thereby ensuring the integrity of the conductive network of the current collector 11. The first insulating layer 12 is bonded to the first coating layer 17a and the first surface 1121 of the empty foil segment 11b. For example, the first coating layer 17a has a first segment 17a1 protruding toward the empty foil segment 11b. The first active material layer 15a is not provided on the first segment 17a1. The first insulating layer 12 can be bonded to the first segment 17a1 and the first surface 1121 of the empty foil segment 11b. The sufficient connection area improves the connection strength of the first insulating layer 12. The end of the first segment 17a1 facing the first transition portion 14a can be set to a smooth arc shape to ensure that the first insulating layer 12 smoothly transitions from the empty foil segment 11b to the first segment 17a1, reduce bubbles and wrinkles, and improve the bonding strength between the first insulating layer 12 and the first segment 17a1.

[0064] Similarly, a second coating layer 17b may also be provided on the second surface 1131 of the coating segment 11a, and the second active material layer 15b may be provided on the surface of the first coating layer 17a facing away from the coating segment 11a. The thickness of the second coating layer 17b along the thickness direction of the current collector 11 (second direction Y) is T3 μm, 0.5 μm ≤ T3 ≤ 4 μm, which can effectively protect the second metal layer 113 of the current collector 11 from being punctured by the sharp particles of the second active material layer 15b, thereby ensuring the integrity of the conductive network of the current collector 11. The second insulating layer 13 is bonded to the second coating layer 17b and the second surface 1131 of the empty foil segment 11b. For example, the second coating layer 17b has a second section 17b1 protruding toward the empty foil segment 11b, and the second active material layer 15b is not provided on the second section 17b1. The second insulating layer 13 can be bonded to the second section 17b1 and the second surface 1131 of the empty foil segment 11b to ensure the connection area of ​​the second insulating layer 13.

[0065] Preferably, along the width direction (first direction X) of the current collector 11, the length of the first segment 17a1 is L4 mm, with 1 mm ≤ L4 ≤ 1.8 mm. The first segment 17a1 protrudes sufficiently to reduce the risk of the portion of the current collector 11 not provided with the active material layer piercing the separator near the first metal layer 112, thereby reducing the risk of short circuits. Similarly, the length of the second segment 17b1 is L5 mm, with 1 mm ≤ L5 ≤ 1.8 mm, to reduce the risk of the portion of the current collector 11 not provided with the active material layer piercing the separator near the second metal layer 113. Among them, when observed along the thickness direction of the current collector 11 (second direction Y), the first segment 17a1 and the second segment 17b1 are offset from each other by 0 to 0.2 mm. Limiting the offset range can ensure the consistency of the electrical connection process between the first transition portion 14a and the second transition portion 14b. If the offset range is too large, the electrical connection between the first transition portion 14a and the second transition portion 14b and the empty foil segment 11b may be inconsistent. For example, the first transition portion 14a is electrically connected to the first metal layer 112, and the second transition portion 14b is electrically connected to the second coating 17b.

[0066] Regarding the materials of the first coating 17a and the second coating 17b, the first coating 17a and / or the second coating 17b include inorganic ceramics, insulating organic polymers, and conductive particles. The inorganic ceramics include at least one of alumina, boehmite, silica, calcite, magnesite, barium sulfate, lead sulfate, calcium sulfate, or copper sulfate. The insulating organic polymer includes at least one of polyethylene, polypropylene, polybutene, polypentene, polyhexene, polyvinyl alcohol, polyacrylamide, polyester fiber, polyvinyl alcohol-polyester, polyethylene glycol ester, polycaprolactone, polybutylene succinate, polyether ester, polycarbonate, or rubber. The conductive particles include conductive carbon or conductive carbon nanotubes, such as carbon black, graphene, or acetylene black.

[0067] Referring to Figure 10, in some embodiments, the pole piece 10 further includes a first adhesive layer 18a, which is disposed on a surface of the first transition portion 14a facing away from the second transition portion 14b. The first adhesive layer 18a can cover some burrs on the first transition portion 14a, thereby reducing the risk of burrs penetrating the isolation film 20 near the first metal layer 112. The thickness of the first adhesive layer 18a along the thickness direction of the current collector 11 (the second direction Y) is T7 μm, with 5 μm ≤ T7 ≤ 40 μm. This can reduce the risk of burrs penetrating the first adhesive layer 18a while ensuring stable bonding. Furthermore, the space occupied by the first adhesive layer 18a can be minimized, thereby increasing the volumetric energy density of the battery.

[0068] Observed from the direction from the first adhesive layer 18a to the first transition portion 14a (opposite to the second direction Y), the first adhesive layer 18a covers the welding portion 16. The first adhesive layer 18a protects the welding area between the welding portion 16 and the first transition portion 14a, ensuring insulation of this area. Furthermore, the first adhesive layer 18a covers some burrs on the welding portion 16, further reducing the risk of burrs piercing the isolation film 20 near the first metal layer 112. The first adhesive layer 18a can be made of a polyolefin hot melt adhesive, which is resistant to electrolyte corrosion and can improve the battery's service life and bonding reliability. In other embodiments, the first adhesive layer 18a can also be made of a swelling hot melt adhesive, for example.

[0069] Optionally, inorganic salt pigments may be added to the first adhesive layer 18a, such as brighter colors such as blue, red or green. When the first adhesive layer 18a is disposed on the first adapter portion 14a, CCD visual recognition may be used to determine whether there is any coating leakage, thereby ensuring the integrity of the first adhesive layer 18a.

[0070] In some embodiments, the pole piece 10 further includes a second adhesive layer 18b, which is disposed on the surface of the second transition portion 14b facing away from the first transition portion 14a. The second adhesive layer 18b can cover some burrs on the second transition portion 14b, thereby reducing the risk of burrs penetrating the isolation film 20 near the second metal layer 113. Along the thickness direction of the current collector 11 (the second direction Y), the thickness of the second adhesive layer 18b is T8 μm, with 5 μm ≤ T8 ≤ 30 μm. This ensures stable adhesion while stably covering burrs, minimizing the space occupied by the first adhesive layer 18a, and increasing the volumetric energy density of the battery. It should be noted that, taking Figure 10 as an example, the above-mentioned first adhesive layer 18a is located above the current collector 11. Under the action of gravity, its burrs are more likely to pierce the first adhesive layer 18a, while the second adhesive layer 18b below does not have this problem or the probability of such problem occurring is relatively small. Therefore, the thickness of the second adhesive layer 18b below can be set to be slightly smaller than the thickness of the first adhesive layer 18a to fully improve the volume energy density of the battery.

[0071] Observed along the direction from the second adhesive layer 18b to the second transition portion 14b (second direction Y), the second adhesive layer 18b covers the welding portion 16. The second adhesive layer 18b protects the welding area between the welding portion 16 and the second transition portion 14b, ensuring insulation of this area. The second adhesive layer 18b also covers some burrs on the welding portion 16, further reducing the risk of burrs piercing the isolation film 20 near the second metal layer 113. Similar to the first adhesive layer 18a, the material of the second adhesive layer 18b can also be a polyolefin hot melt adhesive, which can extend the battery life.

[0072] Preferably, referring to FIG11 , the first adhesive layer 18a is bonded to the first insulating layer 12, so that the first metal layer 112 exposed by the empty foil segment 11b is completely insulated and isolated, which not only reduces the occurrence of short circuits but also improves the tear resistance of the empty foil segment 11b. The width of the first adhesive layer 18a along the width direction of the current collector 11 (the first direction X) is W3mm, 1.2mm≤W3≤5mm, ensuring that the first adhesive layer 18a covers the welding portion 16 while facilitating bonding with the first insulating layer 12. Similarly, the second adhesive layer 18b is bonded to the second insulating layer 13, so that the second metal layer 113 exposed by the empty foil segment 11b is completely isolated, further reducing the occurrence of short circuits and improving the tear resistance of the empty foil segment 11b. The width of the second adhesive layer 18b along the width direction of the current collector 11 (the first direction X) is W4mm, 1.2mm≤W4≤5mm, ensuring that the second adhesive layer 18b covers the welding portion 16 while facilitating bonding with the second insulating layer 13.

[0073] In the embodiment of the present application, by providing a first transition portion 14a and a second transition portion 14b, the first transition portion 14a is electrically connected to the first metal layer 112 of the current collector 11, and the second transition portion 14b is electrically connected to the second metal layer 113 of the current collector 11. This double-sided electrical connection improves the reliability of the electrical connection between the two transition portions and the current collector 11, and alleviates the problem of the difficulty in symbiotic bonding between the polymer material and the transition portion. At the same time, the first insulating layer 12 partially covers the empty foil segment 11b, which can improve the strength of the empty foil segment 11b, reduce deformation and tearing of the empty foil segment 11b, and improve the resistance of the electrode 10 to mechanical damage. In addition, limiting the distance between the first transition portion 14a and the first insulating layer 12 to L1mm, 0mm≤L1≤1mm, can effectively reduce the risk of burrs piercing the isolation membrane 20 close to the first metal layer 112, and limiting the distance between the second transition portion 14b and the second insulating layer 13 to L2mm, 0mm≤L2≤1mm, can further reduce the risk of burrs piercing the isolation membrane 20, thereby reducing the risk of battery short circuit.

[0074] In a second aspect, an embodiment of the present application further provides a secondary battery, comprising a pole piece as described in any embodiment of the first aspect above.

[0075] In the embodiment of the present application, a lithium-ion battery is taken as an example and a drop test is performed on it.

[0076] Example 1

[0077] Preparation of lithium-ion batteries

[0078] (1) Preparation of positive electrode sheet: The positive electrode active materials lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75wt%, and stirred evenly.

[0079] Polyethylene terephthalate was used as the polymer layer. A first metal layer and a second metal layer made of aluminum were evaporated on both surfaces of the polymer layer. The slurry was applied to the surface of the first metal layer, and a blank positive electrode foil section was reserved. The width W1 of the blank foil section was 3mm. The slurry was dried to obtain a positive electrode sheet coated with an active material layer on one side. The above steps were repeated on the second metal layer to obtain a positive electrode sheet coated with a positive active material layer on both sides.

[0080] (2) Preparation of negative electrode sheet: Graphite was used as the negative electrode active material. The negative electrode active material graphite, binder styrene-butadiene rubber (SBR) and thickener sodium carboxymethyl cellulose (CMC) were mixed in a weight ratio of 96:2:2, and deionized water was added as a solvent to prepare a slurry with a solid content of 70 wt%, which was then stirred evenly.

[0081] Copper foil is used as the negative electrode current collector. The slurry is evenly coated on one surface of the copper foil, leaving a blank section of negative electrode foil on this surface. The slurry is dried to obtain a negative electrode sheet coated with a negative electrode active material layer on one side. The above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a positive electrode active material layer on both sides.

[0082] (3) Preparation of electrolyte: In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC:EMC:DEC = 30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the basic organic solvent to dissolve and mix evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0083] (4) Preparation of isolation membrane: A polyethylene porous membrane is used as a substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one surface of the substrate layer as a separator (CCS), wherein the mass percentage of alumina ceramic in the ceramic layer is 95%.

[0084] (5) Preparation of electrode assembly: Aluminum sheets were selected as positive electrode transition tabs (one of the first transition tabs was the first transition portion, and the other was the second transition portion). The first transition portion was welded to the first metal layer of the negative electrode current collector, and the second transition portion was welded to the second metal layer. Polyolefin hot melt adhesive (first insulating layer) was used to bond the first metal layer of the empty foil segment, wherein the distance L1 from the first transition portion to the first insulating layer was 1 mm. Another polyolefin hot melt adhesive was used to bond the second metal layer of the empty foil segment, wherein the distance L2 from the second transition portion to the second insulating layer was 1 mm.

[0085] A nickel sheet is used as the negative electrode transfer tab, which is directly welded to the empty foil section of the copper foil current collector. The positive electrode sheet, separator, and negative electrode sheet are stacked and wound to form an electrode assembly for later use.

[0086] (6) Electrode assembly: Place the aluminum-plastic film with the cavities formed in it into an assembly fixture, with the cavities facing upward. Place the electrode assembly in the cavities, and install seals at the two transition parts. Apply external force to tighten. Then, place another aluminum-plastic film with the cavities formed in it, with the cavities facing downward, over the electrode assembly. Heat-seal the two aluminum-plastic films around each other using hot pressing to obtain an assembled electrode assembly.

[0087] (7) Liquid injection packaging: The assembled electrode assembly is injected with electrolyte, and after vacuum packaging, static standing, hot pressing, shaping and other processes, the lithium-ion battery is produced.

[0088] The data parameters of Examples 2 to 8 and Comparative Examples 1 to 3 can be found in Table 1 below, where:

[0089] In Comparative Example 1, only aluminum foil was used as the current collector, while the other comparative examples and examples all used composite current collectors with a polymer layer;

[0090] In Example 8, a mixed slurry of aluminum oxide, polyethylene, and carbon black in a weight ratio of 97.5:2:0.5 was used. This slurry was first applied to the first metal layer. After drying, a first coating layer was formed on the first metal layer. The active material layer slurry was then applied to the coating layer. This process was repeated for the second metal layer.

[0091] Drop test:

[0092] Lithium-ion batteries were preconditioned at 25°C and allowed to stand at room temperature for 60 minutes. The batteries were then placed in a fixture and dropped from a height of 1.5 meters using a drop device in the following order: head-to-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°). 100 batteries were tested per group. After the drop test, the appearance of the lithium-ion batteries was inspected. The pass criteria for the drop test were: no smoke, no fire, no leakage, and no tearing of the tabs (the first and second adapters are the tabs).

[0093] Table 1

[0094] According to Table 1 above, combined with Examples 1 to 7 and Comparative Example 1, it can be seen that when a composite current collector having a polymer layer is used, the risk of lithium-ion battery drop failure can be effectively reduced. This is because the polymer layer serves as the mechanical performance process skeleton of the current collector. The polymer has better deformation ability and ductility than metal. The first metal layer and the second metal layer can be appropriately thinned, resulting in a certain weight reduction. This not only improves the gravimetric energy density, but also reduces the risk of drop collision failure due to lighter weight. At the same time, the thinning of the metal layer reduces the metal burrs generated when the lithium-ion battery is damaged by mechanical collision, which can reduce the burrs from piercing the separator, thereby reducing the risk of internal short circuit failure of the lithium-ion battery.

[0095] Combining Examples 1 to 7 and Comparative Examples 2 and 3, it can be seen that when the distance between the first adapter and the first insulating layer satisfies 0≤L1≤1, and the distance between the second adapter and the second insulating layer satisfies 0≤L2≤1, the drop failure of the lithium-ion battery can be effectively reduced. This is because the provision of the insulating layer can improve the tear resistance of the adapter and the current collector, and at the same time, the two insulating layers can cover the burrs of the metal layer of the empty foil segment, reducing the burrs from piercing the isolation membrane, thereby reducing the occurrence of short circuits. In Comparative Examples 2 and 3, the distance is too large, resulting in some burrs not being covered, so the risk of burrs piercing the isolation membrane increases, resulting in a weakening of the collision resistance of the lithium-ion battery.

[0096] In Example 8, the risk of drop failure is reduced compared to Example 4 due to the provision of the first and second coating layers. This is because the two coating layers effectively protect the two metal layers of the current collector from being punctured by the sharp particles of the active material layer, thus ensuring the integrity of the current collector's conductive network.

[0097] Example 9 differs from Example 8 in that the first and second transition portions are welded using roller welding, forming a weld mark (weld portion) between the first and second transition portions. The weld mark is not welded to the first and second metal layers of the positive electrode current collector. The distance L3 between the weld mark and the first insulating layer is 0.5 mm, and the distance L7 between the weld mark and the second insulating layer is 0.5 mm.

[0098] The relevant parameters of Examples 10 to 20 are shown in Table 2 below.

[0099] In Example 19, polyolefin hot melt adhesive is used as the first adhesive layer, and the first adhesive layer is applied to cover the welding portion on the side close to the first metal layer; and this operation is repeated on the side close to the second metal layer.

[0100] In Example 20, the first adhesive layer is connected to the first insulating layer, and the second adhesive layer is connected to the second insulating layer.

[0101] Table 2

[0102] According to Table 2 above, combined with Examples 14 to 18, when the distance L3mm between the weld and the first or second insulating layer is 0≤L3≤1, the risk of lithium-ion battery drop failure is effectively reduced. This is due to the provision of a roller weld mark, which improves the welding stability of the first and second transition parts and the current collector, enhancing impact resistance. Furthermore, the limitation of 0≤L3≤1 ensures that the insulating layer covers most burrs, reducing the risk of burrs piercing the separator. Furthermore, the provision of the weld ensures good contact between the first and second transition parts, achieving a double-sided electrical connection and improving current carrying capacity.

[0103] In Example 19, the provision of a first adhesive layer and a second adhesive layer can reduce some burrs at the weld, reducing the risk of burrs piercing the separator, isolating the weld from the negative electrode, and further reducing the risk of short circuits. In Example 20, the first adhesive layer is connected to the first insulating layer, and the second adhesive layer is connected to the second insulating layer. This can limit the shrinkage of each adhesive layer and insulating layer, ensuring that the exposed first and second metal layers of the hollow foil segment are substantially completely insulated. This not only reduces the risk of short circuits but also improves the tear resistance of the hollow foil segment.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Based on the concept of the present application, the technical features in the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations in different aspects of the present application as described above. For the sake of simplicity, they are not provided in detail. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A pole piece, characterized in that, Comprising: A current collector, along the thickness direction of the current collector, the current collector includes a first metal layer, a polymer layer, and a second metal layer arranged in sequence. The first metal layer has a first surface facing away from the polymer layer, and the second metal layer has a second surface facing away from the polymer layer; along the width direction of the current collector, the current collector includes a connected coating section and an empty foil section; A first insulating layer, disposed on one side of the first surface of the first metal layer, a part of the first insulating layer is disposed on the coating section, and another part is disposed on the empty foil section; A first connection part, electrically connected to the current collector on the first surface of the empty foil section, the distance between the first connection part and the first insulating layer is L1 mm, 0 mm ≤ L1 ≤ 1 mm.

2. The electrode tab according to claim 1, wherein The electrode sheet further includes a second insulating layer, the second insulating layer is disposed on one side of the second surface of the second metal layer, a part of the second insulating layer is disposed on the coating section, and another part is disposed on the empty foil section; A second connection part, electrically connected to the current collector on the second surface of the empty foil section, the distance between the second connection part and the second insulating layer is L2 mm, 0 mm ≤ L2 ≤ 1 mm.

3. The pole piece according to claim 2, wherein, 0 mm ≤ L1 ≤ 0.5 mm, 0 mm ≤ L2 ≤ 0.5 mm.

4. The pole piece according to claim 2 or 3, characterized in that, The electrode sheet further includes at least two welding parts, the welding parts are electrically connected to the first connection part and the second connection part, and at least one of the welding parts is electrically connected to the current collector.

5. The pole piece according to any one of claims 2-4, characterized in that, Along the width direction of the current collector, the distance between the welding part and the first insulating layer or the second insulating layer is L3 mm, 0 mm ≤ L3 ≤ 1 mm, L3 > L1, L3 > L2.

6. The pole piece according to any one of claims 1-5, characterized in that, A first coating is provided on the first surface of the coating section, the first insulating layer bonds the first coating and the first surface of the empty foil section, and a first active material layer is provided on the surface of the first coating facing away from the coating section; A second coating is provided on the second surface of the coating section, the second insulating layer bonds the second coating and the second surface of the empty foil section, and a second active material layer is provided on the surface of the second coating facing away from the coating section.

7. The electrode tab according to claim 6, wherein The first coating has a first section disposed close to the empty foil section, and the first active material layer is not provided on the first section. Along the width direction of the current collector, the length of the first section is L4 mm, 1 mm ≤ L4 ≤ 1.8 mm; A second section of the second coating is disposed close to the empty foil section, and the second active material layer is not provided on the second section. Along the width direction of the current collector, the length of the second section is L5 mm, 1 mm ≤ L5 ≤ 1.8 mm.

8. The electrode sheet according to claim 6, wherein The first coating and / or the second coating includes inorganic ceramics, insulating organic polymers, and conductive particles; The inorganic ceramics includes at least one of alumina, boehmite, silica, calcite, magnesite, barium sulfate, lead sulfate, calcium sulfate, or copper sulfate; The insulating organic polymer includes at least one of polyethylene, polypropylene, polybutene, polyisopentene, polyhexene, polyvinyl alcohol, polyacrylamide, polyester fiber, polyvinyl alcohol-polyester, polyethylene glycol ester, polycaprolactone, polybutylene succinate, polyether ester, polycarbonate, or rubber; The conductive particles include carbon black, graphene, or acetylene black.

9. The pole piece according to claim 6, characterized in that, The electrode sheet satisfies at least one of the following conditions, along the thickness direction of the current collector, a), The thickness of the current collector is T1 μm, 4 μm ≤ T1 ≤ 20 μm; b), The thickness of the first coating is T2 μm, 0.5 μm ≤ T2 ≤ 4 μm; c), The thickness of the second coating is T3 μm, 0.5 μm ≤ T3 ≤ 4 μm; d), The thickness of the first connection part is T4 μm, 8 μm ≤ T4 ≤ 15 μm; e), The thickness of the second connection part is T5 μm, 6 μm ≤ T5 ≤ 10 μm.

10. The pole piece according to claim 4, characterized in that, The electrode sheet satisfies at least one of the following conditions, f), Along the thickness direction of the current collector, the thickness of the welding part is T6 μm, 20 μm ≤ T6 ≤ 50 μm; g), Along the width direction of the current collector, the width of the empty foil section is W1 mm, 1 mm ≤ W1 ≤ 5 mm; h), Along the width direction of the current collector, the width of a single welding part is W2 mm, 1 mm ≤ W2 ≤ 3 mm.

11. The pole piece according to any one of claims 4, 5, and 10, characterized in that, The electrode sheet further includes a first adhesive layer and a second adhesive layer; The first adhesive layer is disposed on the surface of the first connection part facing away from the second connection part. When observing along the direction from the first adhesive layer to the first connection part, the first adhesive layer covers the welding part; The second adhesive layer is disposed on the surface of the second connection part facing away from the first connection part. When observing along the direction from the second adhesive layer to the second connection part, the second adhesive layer covers the welding part.

12. The electrode sheet according to claim 11, wherein, The first adhesive layer bonds the first insulating layer, and the second adhesive layer bonds the second insulating layer.

13. The pole piece according to claim 11, characterized in that, The electrode sheet satisfies at least one of the following conditions; i), Along the width direction of the current collector, the width of the first adhesive layer is W3 mm, 1.2 mm ≤ W3 ≤ 5 mm; j), Along the width direction of the current collector, the width of the second adhesive layer is W4 mm, 1.2 mm ≤ W4 ≤ 5 mm; k), Along the thickness direction of the current collector, the thickness of the first adhesive layer is T7 μm, 5 μm ≤ T7 ≤ 40 μm; l), Along the thickness direction of the current collector, the thickness of the second adhesive layer is T8 μm, 5 μm ≤ T8 ≤ 30 μm.

14. The electrode tab according to claim 11, wherein, The first adhesive layer and / or the second adhesive layer includes a polyolefin hot melt adhesive.

15. The electrode tab according to claim 14, characterized in that, In the thickness direction of the current collector, the thickness of the first insulating layer is T9 μm, where 15 μm ≤ T9 ≤ 40 μm, and the thickness of the second insulating layer is T 10 μm, where 15 μm ≤ T 10 ≤ 40 μm; Along the width direction of the current collector, the width of the first insulating layer is W5 mm, 1.5 mm ≤ W5 ≤ 4 mm, and the width of the second insulating layer is W6 mm, 1.5 mm ≤ W6 ≤ 4 mm.

16. The pole piece according to claim 15, characterized in that, 0.1 mm ≤ W5 - W6 ≤ 0.5 mm.

17. A secondary battery, characterized in that, Including the electrode sheet according to any one of claims 1 to 16.

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