Electrode plate, electrode assembly and secondary battery

Abstract

The utility model provides a pole piece, an electrode assembly and a secondary battery. The first aspect of the utility model provides a pole piece which comprises a composite current collector, an active material layer and a third metal layer, the composite current collector comprises a base film, a first metal layer and a second metal layer, the first metal layer and the second metal layer are arranged on the surface of the base film, the composite current collector comprises a composite current collector body and a protruding part formed by extending outwards from one side of the composite current collector body, and an active material layer is arranged on the surface, away from the base film, of the composite current collector body. The surface of the projection away from the base film is connected with the third metal layer. The pole piece provided by the utility model is used for improving the overflowing capability of the composite current collector and improving the performance of the battery.

Description

Technical Field

[0001] The utility model relates to a pole piece and a secondary battery, and relates to the technical field of secondary batteries. Background Art

[0002] With the popularity of new energy vehicles, the requirements for the mileage and safety of new energy vehicles are getting higher and higher. As the energy storage and power supply equipment of new energy vehicles, the energy density and safety of secondary batteries have received much attention in this field. Secondary batteries refer to batteries that can continue to be used by activating the active materials by charging after the battery is discharged. They mainly include pole pieces, diaphragms, electrolytes and shells.

[0003] The pole piece mainly includes a current collector and an active material layer arranged on the surface of the current collector, wherein the current collector is generally a pure metal foil. In order to improve the safety and energy density of secondary batteries, a composite current collector has been developed in this field. The composite current collector is a current collector composed of a polymer material and a metal, which includes a base film composed of a polymer material and a metal layer located on the upper and lower surfaces of the base film. Compared with pure metal foil, the polymer material has a low density and light weight, which helps to reduce the mass of the current collector and thus reduce the energy density of the secondary battery; in addition, the composite current collector has a small burr size when it is punctured, and because the polymer material has an insulating effect, it can effectively control the thermal runaway of the secondary battery, reduce the risk of thermal explosion of the secondary battery, and improve the safety of the secondary battery.

[0004] Because the base film separates the metal layers on both sides, the current cannot be transmitted between the two metal layers, resulting in poor current flow capacity of the current collector. When charging and discharging at a high rate, the performance of the composite current collector is significantly worse than that of traditional pure metal foil. Utility Model Content

[0005] The utility model provides a pole piece, which is used for improving the flow capacity of a composite current collector and improving the performance of a battery.

[0006] The utility model also provides an electrode assembly and a secondary battery comprising the electrode sheet.

[0007] The first aspect of the utility model provides a pole piece, comprising:

[0008] A composite current collector, the composite current collector comprising a base film 11, a first metal layer 12 disposed on a first surface of the base film 11, and a second metal layer 13 disposed on a second surface of the base film 11; the composite current collector 1 comprises a composite current collector body 101 and a protrusion 102 extending outward from one side of the current collector body 101;

[0009] An active material layer 2, wherein the active material layer 2 is disposed on the third surface and / or the fourth surface of the current collector body 101;

[0010] A third metal layer 3, one end of the third metal layer 3 is connected to the fifth surface and the sixth surface of the protrusion 102, and the other end extends out of the outside of the composite current collector 1 along the width direction of the pole piece; along the z direction of the pole piece, the ratio of the size Z1 of the third metal layer 3 to the size Z2 of the composite current collector 1 is 0.5 to 5.

[0011] In the pole piece as described above, the ratio of the size Z1 of the third metal layer 3 to the size Z2 of the composite current collector 1 is 1.5-3.

[0012] For the pole piece as described above, along the z direction of the pole piece, the sizes of the first metal layer 12 and the second metal layer 13 are the same or different.

[0013] For the pole piece as described above, along the z direction of the pole piece, when the size Z3 of the first metal layer 12 is larger than the size Z4 of the second metal layer 13, the size Z5 of the active material layer 2 disposed on the third surface of the current collector body 101 is also larger than the size Z6 of the active material layer 2 disposed on the fourth surface of the current collector body 101;

[0014] Alternatively, along the z direction of the pole piece, when the size of the first metal layer 12 is smaller than the size of the second metal layer 13 , the size Z5 of the active material layer 2 arranged on the third surface of the current collector body 101 is also larger than the size Z6 of the active material layer 2 arranged on the fourth surface of the current collector body 101 .

[0015] For the pole piece as described above, along the z direction of the pole piece, the size Z3 of the first metal layer 12 is 0.5-5 μm;

[0016] And / or, along the z direction of the pole piece, a size Z4 of the second metal layer 13 is 0.5-5 μm.

[0017] For the pole piece as described above, along the z direction of the pole piece, the sizes of the third metal layer 3 arranged on the fifth surface and the sixth surface of the protruding portion 102 are the same or different.

[0018] For the pole piece as described above, along the z direction of the pole piece, when the size of the third metal layer 3 disposed on the fifth surface of the protrusion 102 is larger than the size of the third metal layer 3 disposed on the sixth surface of the protrusion 102, the size of the active material layer 2 disposed on the third surface of the current collector body 101 is also larger than the size of the active material layer 2 disposed on the fourth surface of the current collector body 102;

[0019] Alternatively, along the z direction of the pole piece, when the size of the third metal layer arranged on the fifth surface of the protrusion is smaller than the size of the third metal layer 3 arranged on the sixth surface of the protrusion 102, the size of the active material layer 2 arranged on the third surface of the current collector body 101 is also smaller than the size of the active material layer 2 arranged on the fourth surface of the current collector body 101.

[0020] For the pole piece as described above, along the z direction of the pole piece, the size of the third metal layer 3 is 4-16 μm.

[0021] For the pole piece as described above, along the y direction of the pole piece, the size of the contact area between the third metal layer 3 and the protrusion 102 is Y1, and the size of the third metal layer 3 is Y2, 0.01≤Y1 / Y2≤0.5.

[0022] For the pole piece as described above, Y1 is 4 to 20 mm.

[0023] The pole piece as described above further comprises an insulating layer 4, which is arranged on at least a portion of the surface of the first metal layer 12 and / or the second metal layer 13 away from the base film 11, and is located on a side of the active material layer 2 close to the third metal layer 3. Figure 5

[0024] For the pole piece as described above, along the y direction of the pole piece, the distance between the insulating layer 4 and the third metal layer 3 is Y3 mm, the surface density of the active material layer 2 is A mg / cm2, and 0.5≤Y3 / A≤2.

[0025] For the pole piece as described above, along the y direction of the pole piece, the distance between the insulating layer 4 and the third metal layer 3 is Y3, the distance between the active material layer 2 and the third metal layer 3 is Y4, and 0.02≤Y3 / Y4≤0.50.

[0026] The utility model provides an electrode assembly, comprising a plurality of pole pieces and a fourth metal layer as described above, wherein the third metal layers 3 in the plurality of pole pieces are connected, and the fourth metal layer is connected to one end of the third metal layer.

[0027] The utility model provides a secondary battery, comprising the electrode assembly and a shell sealing the electrode assembly, wherein one end of the fourth metal layer away from the third metal layer is located outside the shell.

[0028] The pole piece provided by the utility model is connected to a third metal layer on the composite current collector, and the third metal layer helps to realize the current transfer between the two metal layers, thereby improving the current carrying capacity of the composite current collector and improving the performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0030] Figure 1 A schematic diagram of the structure of a pole piece provided in one embodiment of the utility model;

[0031] Figure 2 A schematic diagram of the structure of a composite current collector provided in one embodiment of the utility model;

[0032] Figure 3 A schematic diagram of the structure of a pole piece provided in one embodiment of the utility model;

[0033] Figure 4 A schematic diagram of the structure of a pole piece provided in one embodiment of the utility model;

[0034] Figure 5 A schematic diagram of the structure of a pole piece provided by another embodiment of the utility model;

[0035] Figure 6 A schematic structural diagram of a composite current collector provided in yet another embodiment of the present invention.

[0036] Description of reference numerals:

[0037] 1-composite current collector;

[0038] 11-basement membrane;

[0039] 12- first metal layer;

[0040] 13- second metal layer;

[0041] 101-composite current collector body;

[0042] 102- protrusion;

[0043] 2-active material layer;

[0044] 3-third metal layer;

[0045] 4- Insulation layer. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the utility model clearer, the technical solution in the embodiment of the utility model will be clearly and completely described below in combination with the embodiment of the utility model. Obviously, the described embodiment is a part of the embodiment of the utility model, not all the embodiments. Based on the embodiment of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0047] Figure 1 This is a schematic diagram of the structure of a pole piece provided in one embodiment of the utility model. Figure 2 A schematic diagram of the structure of a composite current collector provided in one embodiment of the utility model is shown in FIG. Figures 1-2 As shown, the pole piece includes a composite current collector 1, an active material layer 2 and a third metal layer 3; wherein the composite current collector 1 includes a base film 11, a first metal layer 12 arranged on the first surface of the base film 11 and a second metal layer 13 arranged on the second surface of the base film 11, and the composite current collector 1 includes a composite current collector body 101 and a protrusion 102 extending outward from one side of the composite current collector body 101; the third surface and / or the fourth surface of the composite current collector body 101 is provided with the active material layer 2, the fifth surface and the sixth surface of the protrusion 102 are provided with the third metal layer 3, and the third metal layer 3 located on the fifth surface and the sixth surface of the protrusion 102 extends out of the outside of the composite current collector 1 along the width direction of the pole piece and is connected as a whole, so that the currents of the first metal layer 12 and the second metal layer 13 located on the first surface and the second surface of the base film 11 are gathered together.

[0048] In the present invention, "thickness" refers to the dimension along the thickness direction of the electrode, and the thickness direction is the same as the conventional definition in the field, that is, Figures 1-2 The z direction in the pole piece shown; in addition, the length direction and the width direction are the same as the conventional definitions in the field, that is, the x direction of the pole piece is the length direction of the pole piece, and the y direction is the width direction of the pole piece; the definitions of the composite current collector, the active material layer and the third metal layer are the same as those of the pole piece.

[0049] Along the z direction of the pole piece, the ratio of the size Z1 of the third metal layer 3 to the size Z2 of the composite current collector 1 is 0.5-5, specifically 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5 or any two thereof.

[0050] Furthermore, the ratio of the size Z1 of the third metal layer 3 to the size Z2 of the composite current collector 1 is 1.5 to 3; by increasing the thickness of the third metal layer 3, it helps to improve the ability of current to pass through the first metal layer 12 and the second metal layer 13, reduce the internal resistance of the electrode, reduce the temperature rise of the secondary battery during use, and improve the performance and life of the secondary battery; at the same time, if the thickness of the third metal layer 3 is too high, it will also affect the welding yield between it and the first metal layer 12 and the second metal layer 13.

[0051] Furthermore, the ratio of the size Z1 of the third metal layer 3 to the size Z2 of the composite current collector 1 is 2; when the thickness of the third metal layer 3 is greater than twice the thickness of the composite current collector 1, it will affect the welding yield of the composite current collector 1 and the third metal layer 3. When the thickness ratio is less than 2 times, the temperature rise of the battery including the pole piece is higher.

[0052] It can be understood that the internal resistance of the electrode is also affected by the first metal layer 12 and the second metal layer 13. Therefore, in the composite current collector 1, the thickness of the first metal layer 12 and the second metal layer 13 should not be too low; specifically, the total thickness of the first metal layer 12 and the second metal layer 13 arranged on the first surface and the second surface of the base film 11 is not less than 20% of the total thickness Z2 of the composite current collector; by increasing the thickness of the first metal layer 12 and the second metal layer 13, on the basis of using the same material, it helps to further improve the conductivity of the composite current collector 1, reduce the internal resistance of the electrode, and improve the performance and life of the secondary battery.

[0053] Furthermore, considering the safety of the composite current collector 1 and the energy density of the battery, the total thickness of the first metal layer 12 and the second metal layer 13 arranged on the first surface and the second surface of the base film 11 is not less than 80% of the total thickness Z2 of the composite current collector.

[0054] In a specific embodiment, along the z direction of the pole piece, the sizes of the first metal layer 12 and the second metal layer 13 may be the same or different, that is, the thicknesses of the first metal layer 12 and the second metal layer 13 may be the same or different.

[0055] Based on the thickness of the first metal layer 12 and the second metal layer 13, their ability to provide current will also change, such as Figure 3 As shown, along the z direction of the electrode piece, when the size Z3 of the first metal layer 12 is equal to the size Z4 of the second metal layer 13, the size Z5 of the active material layer 2 arranged on the third surface of the composite current collector body 101 is also equal to the size Z6 of the active material layer 2 arranged on the fourth surface of the composite current collector body 101; that is, when the thickness of the first metal layer 12 and the second metal layer 13 are the same, the thickness of the active material layer 2 connected to the first metal layer 12 is the same as the thickness of the active material layer 2 connected to the second metal layer 13.

[0056] Along the z direction of the electrode sheet, when the size Z3 of the first metal layer 12 is greater than the size Z4 of the second metal layer 13, the size Z5 of the active material layer 2 arranged on the third surface of the composite current collector body 101 is also greater than the size Z6 of the active material layer 2 arranged on the fourth surface of the composite current collector body 101; that is, when the thickness of the first metal layer 12 is greater than the thickness of the second metal layer 13, the thickness of the active material layer 2 connected to the first metal layer 12 is also greater than the thickness of the active material layer 2 connected to the second metal layer 13.

[0057] Along the z direction of the electrode sheet, when the size Z3 of the first metal layer 12 is smaller than the size Z4 of the second metal layer 13, the size Z5 of the active material layer 2 arranged on the third surface of the composite current collector body 101 is also larger than the size Z6 of the active material layer 2 arranged on the fourth surface of the composite current collector body 101; that is, when the thickness of the first metal layer 12 is smaller than the thickness of the second metal layer 13, the thickness of the active material layer 2 connected to the first metal layer 12 is also smaller than the thickness of the active material layer 2 connected to the second metal layer 13.

[0058] Variations in the thickness of the first metal layer 12 and the second metal layer 13 and the thickness of the active material layer 2 loaded thereon help ensure a match between the active material contained in the active material layer 2 and the current that can be provided by the first metal layer 12 / the second metal layer 13 .

[0059] In a specific embodiment, along the z direction of the pole piece, the size Z3 of the first metal layer 12 is 0.5-5 μm, specifically 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or within the range of any two thereof.

[0060] In a specific embodiment, along the z direction of the pole piece, the size Z4 of the second metal layer 13 is 0.5-5 μm, specifically 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or within the range of any two thereof.

[0061] like Figure 4 As shown, along the z direction of the pole piece, when the sizes of the third metal layer 3 arranged on the fifth surface and the sixth surface of the protrusion 102 are the same or different, the thicknesses of the active material layer 2 arranged on the third surface and the fourth surface of the composite current collector body 101 are also the same or different, which helps to ensure the match between the active material contained in the active material layer 2 and the current that can be provided by the third metal layer 3.

[0062] Specifically, along the z direction of the pole piece, when the size Z7 of the third metal layer 3 arranged on the fifth surface of the protrusion 102 is equal to the size Z8 of the third metal layer 3 arranged on the sixth surface of the protrusion 102, the size Z5 of the active material layer 2 arranged on the third surface of the composite current collector body 101 is also the same as the thickness Z6 of the active material layer 2 arranged on the fourth surface of the composite current collector body 101.

[0063] Along the z direction of the pole piece, when the size of the third metal layer 3 arranged on the fifth surface of the protrusion 102 is larger than the size of the third metal layer 3 arranged on the sixth surface of the protrusion 102, the size of the active material layer 2 arranged on the third surface of the composite current collector body 101 is also larger than the size of the active material layer 2 arranged on the fourth surface of the composite current collector body 101.

[0064] Along the z direction of the pole piece, when the size of the third metal layer arranged on the fifth surface of the protrusion is smaller than the size of the third metal layer 3 arranged on the sixth surface of the protrusion 102, the size of the active material layer 2 arranged on the third surface of the composite current collector body 101 is also smaller than the size of the active material layer 2 arranged on the fourth surface of the composite current collector body 101.

[0065] In a specific embodiment, along the z direction of the pole piece, the size of the third metal layer 3 is 4 to 16 μm, specifically 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm or within the range of any two thereof.

[0066] In a specific embodiment, continue to refer to Figure 4 , along the y direction of the pole piece, the size of the contact area between the third metal layer 3 and the protrusion 102 is Y1, and the size of the third metal layer 3 is Y2, 0.01≤Y1 / Y2≤0.5. Y1 / Y2 represents the ratio of the weld area formed by the welding connection between the third metal layer 3 and the first metal layer 12 or the second metal layer 13 to the total width of the third metal layer 3. When Y1 / Y2 is lower than 0.01, the welding strength between the third metal layer 3 and the first metal layer 12 or the second metal layer 13 is reduced, and it is easy to fall off from the composite current collector 1, and the current carrying capacity is low, and the current intensity that can be tolerated is reduced; when Y1 / Y2 is higher than 0.5, it means that the weld is wide, the volume utilization rate is too low, and it is easy to affect the volume energy density of the battery.

[0067] Furthermore, Y1 is 4-20 mm, specifically 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, 20 mm or a range consisting of any two thereof.

[0068] During the cycle of the secondary battery, the negative electrode active material continuously receives ions released from the positive electrode active material. When the positive electrode active material releases too many ions and cannot be completely embedded in the negative electrode active material, these ions will precipitate from the surface of the negative electrode plate, resulting in a decrease in the capacity of the secondary battery. These precipitated ions may even pierce the diaphragm, causing the battery to short-circuit and cause safety problems. Therefore, the negative electrode plate is usually in excess of the positive electrode plate to fully accommodate the ions released from the positive electrode active material. In order to prevent the excessive negative electrode active material layer from short-circuiting in contact with the empty foil of the positive electrode collector, an insulating layer is generally provided on the surface of the positive electrode collector. The position of the insulating layer and the conductive layer will affect the contact between the positive electrode collector and the negative electrode collector, and affect the internal resistance of the battery. Therefore, the utility model defines the size and position of the insulating layer.

[0069] Figure 5 A schematic diagram of the structure of a pole piece provided by another embodiment of the utility model is shown in FIG. Figure 6 A schematic diagram of the structure of a current collector provided by another embodiment of the utility model is shown in FIG. Figures 5-6 As shown, the pole piece further includes an insulating layer 4 , which is disposed on at least a portion of the surface of the first metal layer 12 and / or the second metal layer 13 away from the base film 11 , and is located on a side of the active material layer 2 close to the third metal layer 3 .

[0070] Furthermore, along the y direction of the electrode, the distance between the insulating layer 4 and the third metal layer 3 is Y3 mm, and the surface density of the active material layer 2 is A mg / cm 2 , 0.5≤Y3 / A≤2. As the surface density of the active material layer 2 increases, the electron transmission capacity required under the same conditions becomes stronger. As the distance Y3mm between the third metal layer 3 and the insulating layer 4 decreases, the conductivity of the pole piece becomes stronger. At the same time, shortening the distance Y3 also helps to improve the volume energy density of the battery. Therefore, in the pole piece provided by the utility model, Y3 / A≤2.

[0071] Furthermore, along the y direction of the electrode, the distance between the insulating layer 4 and the third metal layer 3 is Y3, and the distance between the active material layer 2 and the third metal layer 3 is Y4, 0.02≤Y3 / Y4≤0.50, that is, the distance between the position of the weld mark and the insulating layer 4; it can be understood that when Y3 / Y4 is not higher than 0.50, it is beneficial to improve the volume utilization of the battery, but considering the preparation process of the electrode, Y3 / Y4 is generally not less than 0.02.

[0072] It can be understood that the structure of the electrode sheet provided by the present invention is applicable to positive electrode sheets and / or negative electrode sheets, and those skilled in the art can configure it according to needs.

[0073] The second aspect of the utility model provides an electrode assembly, comprising a plurality of pole pieces as described above and a fourth metal layer, wherein the third metal layers 3 in the plurality of pole pieces are connected, and the fourth metal layer is connected to one end of the third metal layer 3 .

[0074] In a specific embodiment, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator located between the positive electrode sheet and the negative electrode sheet, and at least one of the positive electrode sheet and the negative electrode sheet has the electrode sheet structure provided in the first aspect of the utility model.

[0075] During the preparation process, a conventional lamination process or winding process is adopted to stack and assemble the positive electrode sheet, the separator and the negative electrode sheet in sequence to obtain an electrode assembly, and the third metal layer extending from the protruding part of the current collector is connected as a whole, and the fourth metal layer is connected to the end of the third metal layer 3 away from the electrode sheet to achieve the connection between the battery and the external circuit.

[0076] The third aspect of the utility model provides a secondary battery, comprising the electrode assembly and a shell that seals the electrode assembly, wherein one end of the fourth metal layer away from the third metal layer is located outside the shell.

[0077] In a specific embodiment, the secondary battery may be a lithium-ion battery, which includes, in addition to the electrode assembly, a housing for sealing and accommodating the electrode assembly and an electrolyte.

[0078] The shell can be made of conductive metal materials such as aluminum or aluminum alloy; the electrolyte at least includes an organic solvent and a lithium salt.

[0079] In the description of the present invention, it is necessary to understand that the terms "upper" and "lower" etc. indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0080] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood by specific circumstances.

[0081] In the description of the present invention, the terms "first", "second", "third", "fourth", etc., if present, are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so that the embodiments of the present application described herein can, for example, be implemented in an order other than those illustrated or described herein.

[0082] In the description of the present invention, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the previous and next associated objects are in an "or" relationship; in a formula, the character " / " indicates that the previous and next associated objects are in a "division" relationship.

[0083] The above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model is described in detail with reference to the above embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the above embodiments, or replace some or all of the technical features therein with equivalents. These modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the utility model.

Claims

1. A pole piece, characterized in that: include: A composite current collector (1), the composite current collector comprising a base film (11), a first metal layer (12) arranged on a first surface of the base film (11), and a second metal layer (13) arranged on a second surface of the base film (11); the composite current collector (1) comprising a composite current collector body (101) and a protrusion (102) extending outward from one side of the current collector body (101); An active material layer (2), the active material layer (2) being arranged on the third surface and / or the fourth surface of the current collector body (101); A third metal layer (3), one end of the third metal layer (3) is connected to the fifth surface and the sixth surface of the protruding portion (102), and the other end extends out of the composite current collector (1) along the width direction of the pole piece; along the z direction of the pole piece, the ratio of the size Z1 of the third metal layer (3) to the size Z2 of the composite current collector (1) is 0.5 to 5.

2. The pole piece according to claim 1, characterized in that: The ratio of the size Z1 of the third metal layer (3) to the size Z2 of the composite current collector (1) is 1.5 to 3.

3. The pole piece according to claim 1, characterized in that: Along the z direction of the pole piece, the sizes of the first metal layer (12) and the second metal layer (13) are the same or different.

4. The pole piece according to claim 1, characterized in that: Along the z direction of the electrode sheet, when the size Z3 of the first metal layer (12) is greater than the size Z4 of the second metal layer (13), the size Z5 of the active material layer (2) arranged on the third surface of the current collector body (101) is also greater than the size Z6 of the active material layer (2) arranged on the fourth surface of the current collector body (101); Alternatively, along the z direction of the pole piece, when the size of the first metal layer (12) is smaller than the size of the second metal layer (13), the size Z5 of the active material layer (2) arranged on the third surface of the current collector body (101) is also larger than the size Z6 of the active material layer (2) arranged on the fourth surface of the current collector body (101).

5. The pole piece according to any one of claims 1 to 4, characterized in that: Along the z direction of the pole piece, the size Z3 of the first metal layer (12) is 0.5 to 5 μm; And / or, along the z direction of the pole piece, the size Z4 of the second metal layer (13) is 0.5 to 5 μm.

6. The pole piece according to claim 1, characterized in that: Along the z direction of the pole piece, the sizes of the third metal layer (3) arranged on the fifth surface and the sixth surface of the protruding portion (102) are the same or different.

7. The pole piece according to claim 1, characterized in that: Along the z direction of the pole piece, when the size of the third metal layer (3) arranged on the fifth surface of the protruding portion (102) is larger than the size of the third metal layer (3) arranged on the sixth surface of the protruding portion (102), the size of the active material layer (2) arranged on the third surface of the current collector body (101) is also larger than the size of the active material layer (2) arranged on the fourth surface of the current collector body (101); Alternatively, along the z direction of the pole piece, when the size of the third metal layer arranged on the fifth surface of the protrusion is smaller than the size of the third metal layer (3) arranged on the sixth surface of the protrusion (102), the size of the active material layer (2) arranged on the third surface of the current collector body (101) is also smaller than the size of the active material layer (2) arranged on the fourth surface of the current collector body (101).

8. The pole piece according to any one of claims 6 to 7, characterized in that: Along the z direction of the pole piece, the size of the third metal layer (3) is 4 to 16 μm.

9. The pole piece according to claim 1, characterized in that: Along the y direction of the pole piece, the size of the contact area between the third metal layer (3) and the protruding portion (102) is Y1, and the size of the third metal layer (3) is Y2, 0.01≤Y1 / Y2≤0.

5.

10. The pole piece according to claim 9, characterized in that: Y1 is 4~20mm.

11. The pole piece according to claim 1, characterized in that: The pole piece further comprises an insulating layer (4), wherein the insulating layer (4) is arranged on at least a portion of the surface of the first metal layer (12) and / or the second metal layer (13) away from the base film (11), and is located on a side of the active material layer (2) close to the third metal layer (3).

12. The pole piece according to claim 11, characterized in that: Along the y direction of the pole piece, the distance between the insulating layer (4) and the third metal layer (3) is Y3mm, and the surface density of the active material layer (2) is Amg / cm 2 , 0.5≤Y3 / A≤2.

13. The pole piece according to claim 11, characterized in that: Along the y direction of the pole piece, the distance between the insulating layer (4) and the third metal layer (3) is Y3, the distance between the active material layer (2) and the third metal layer (3) is Y4, and 0.02≤Y3 / Y4≤0.

50.

14. An electrode assembly, characterized in that: It comprises several pole pieces and a fourth metal layer as claimed in any one of claims 1 to 13, the third metal layers (3) in several of the pole pieces are connected, and the fourth metal layer is connected to one end of the third metal layer.

15. A secondary battery, characterized in that: The invention comprises the electrode assembly as claimed in claim 14 and a casing for sealing the electrode assembly, wherein one end of the fourth metal layer away from the third metal layer is located outside the casing.

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