Secondary battery and electric equipment

Abstract

The utility model provides a secondary battery and electric equipment, a pole piece assembly in the secondary battery comprises a first pole piece, a second pole piece and a diaphragm, at least one of the first pole piece and the second pole piece comprises a composite current collector, a first conductive layer, an active material layer and an electric conductor, the composite current collector is provided with a tab part and a bearing part which are connected with each other, the active material layer is stacked on the bearing part, the first conductive layer and the active material layer are arranged on the tab part at the same side, the first conductive layer is locally connected with the active material layer, a through hole penetrating through the tab part is formed in the end part, far away from the bearing part, of the tab part, and the through hole is filled with a conductor connected with the first conductive layer. According to the pole piece structure, the electron transmission path between the composite current collector and the active material layer is widened, conductive connection between the pole pieces in the pole piece assembly is achieved through the electric conductor, meanwhile, battery pole lug welding adopting the composite current collector is compatible with an existing process, and the welding difficulty between the pole pieces based on the composite current collector is reduced.

Description

Technical Field

[0001] The present application relates to the technical field of rechargeable batteries, and in particular to a secondary battery and an electrical device. Background Art

[0002] At present, energy conservation and emission reduction are the key to the sustainable development of the automobile industry. Electric vehicles have become an important part of the sustainable development of the automobile industry due to their advantages in energy conservation and environmental protection. Long-range electric vehicles require secondary batteries with high energy density.

[0003] Existing high-energy-density secondary batteries use composite current collectors to replace traditional metal foil current collectors. The composite current collector reduces the amount of metal used by introducing a polymer layer, significantly reducing the weight of the current collector, so that the energy density of the secondary battery using the composite current collector can be increased by 5% to 10%. However, due to the thin thickness of the metal layer in the composite current collector, the transmission internal resistance of electrons or current is large, resulting in poor current capacity of the secondary battery prepared using the composite current collector, which in turn leads to poor rate performance of the secondary battery using the composite current collector. In addition, due to the thin metal layer in the composite current collector and the two metal layers in the composite current collector are not interconnected, the electrode piece and ear welding prepared using the composite current collector is poorly compatible with the existing process, and there are problems of complex welding process and high cost. Utility Model Content

[0004] The technical problem to be solved by the present application is to provide a secondary battery and an electrical device to solve the problems of poor rate performance and current carrying capacity, complex welding process and high cost of the existing secondary batteries using composite current collectors.

[0005] In order to solve the above problems, the present application is implemented through the following technical solutions:

[0006] The present application provides a secondary battery, the secondary battery comprising a pole piece assembly, the pole piece assembly comprising a first pole piece, a second pole piece and a separator for isolating the first pole piece and the second pole piece, one of the first pole piece and the second pole piece is a positive pole piece and the other is a negative pole piece, at least one of the first pole piece and the second pole piece comprises a composite current collector, a first conductive layer, an active material layer and a conductor;

[0007] The composite current collector comprises a pole ear portion and a bearing portion, wherein the pole ear portion is connected to the bearing portion;

[0008] The active material layer is stacked on the supporting portion;

[0009] The first conductive layer and the active material layer are arranged on the same side of the electrode ear, and a part of the first conductive layer is connected to the active material layer;

[0010] The end of the pole ear portion away from the bearing portion is provided with a through hole penetrating the pole ear portion, and the through hole is extended along the thickness direction of the pole ear portion;

[0011] The conductor is filled in the through hole.

[0012] Furthermore, in the secondary battery, the composite current collector comprises two second conductive layers and a polymer layer; two opposite surfaces of the polymer layer are respectively provided with a second conductive layer;

[0013] Wherein, the sum of the thicknesses of the first conductive layer and the second conductive layer on the same side of the composite current collector is 1.5 μm to 12 μm.

[0014] Furthermore, in the secondary battery, the thickness of the first conductive layer is 1 μm to 10 μm.

[0015] Furthermore, in the secondary battery, the end of the pole ear away from the bearing portion has a welding area, the opening end of the through hole is located in the welding area, and the ratio of the total area of ​​the through hole in the welding area to the total area of ​​the welding area is 1 / 5 to 3 / 5.

[0016] Furthermore, in the secondary battery, a plurality of through holes are provided, and in the pole ear portion, a distance between two adjacent through holes is greater than or equal to a target length of the through holes;

[0017] Wherein, when the through hole is circular, the target length is the diameter of the circle; when the through hole is polygonal, the target length is the length of the shortest side of the polygon.

[0018] Furthermore, in the secondary battery, the first conductive layer includes a main body portion and an extension portion which are connected to each other, the main body portion is arranged at the pole ear portion, and the extension portion is connected to the active material layer.

[0019] Furthermore, in the secondary battery, the extension portion extends from the main body portion to the bearing portion along a direction from the pole ear portion to the bearing portion to be connected to the active material layer.

[0020] Furthermore, in the secondary battery, the extension portion has a first side and a second side, the first side is a side of the extension portion connected to the main body portion, and the second side is a side of the extension portion away from the connection side;

[0021] In the extending portion, a thickness of the extending portion close to the first side is greater than or equal to a thickness of the extending portion close to the second side.

[0022] Furthermore, in the secondary battery, the extension portion extends along the thickness direction of the composite current collector in a direction away from the composite current collector and is attached to the active material layer.

[0023] Furthermore, in the secondary battery, the length of the extension track from one end of the extension portion away from the main body portion to one end connected to the main body portion is 1 mm to 10 mm.

[0024] The present application also proposes an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0025] Compared with the prior art, the embodiments of the present application have the following advantages:

[0026] In an embodiment of the present application, a pole piece assembly in a provided secondary battery includes a first pole piece, a second pole piece and a diaphragm for isolating the first pole piece and the second pole piece, at least one of the first pole piece and the second pole piece includes a composite current collector, a first conductive layer, an active material layer and a conductor, and the composite current collector has a pole ear portion and a bearing portion that are connected to each other, the active material layer is stacked on the bearing portion, the first conductive layer and the active material layer are arranged on the pole ear portion on the same side, and a part of the first conductive layer is connected to the active material layer, the transmission path between the composite current collector and the active material layer is widened through the first conductive layer, the speed at which electrons or currents are transmitted between the active material layer and the pole through the composite current collector is accelerated, the resistance to the transmission of electrons between the active material layer and the pole is reduced, and the rate performance and current capacity of the secondary battery using the composite current collector are improved. In addition, a through hole penetrating the pole ear portion is provided at the end of the pole ear portion away from the bearing portion, and the through hole is extended in the thickness direction of the pole ear portion, and the through hole is filled with a conductor, and the conductive connection between different pole pieces is realized by the conductor filled in the through hole, so that the subsequent welding process is compatible with the existing process, thereby reducing the welding difficulty and welding cost between pole pieces based on the composite current collector, and further, the first conductive layer arranged in the pole ear portion increases the effective contact area between the conductor filled in the through hole and the composite current collector, further reducing the resistance of electron transmission between the active material layer and the pole column. The secondary battery provided by the embodiment of the present application improves the rate performance and current carrying capacity of the secondary battery while ensuring the energy density of the secondary battery, and reduces the welding complexity and welding cost between pole pieces in the secondary battery based on the composite current collector.

[0027] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a schematic cross-sectional structural diagram of a pole piece assembly along the thickness direction of the pole piece assembly provided by an embodiment of the present application;

[0029] Figure 2 is a schematic diagram of a top view of a pole ear portion provided in an embodiment of the present application;

[0030] Figure 3 is a schematic diagram of a top view of a pole piece assembly provided in one embodiment of the present application;

[0031] Figure 4 is a schematic cross-sectional structural diagram of a pole piece assembly along the thickness direction of the pole piece assembly provided by another embodiment of the present application;

[0032] Figure 5 is a schematic cross-sectional structural diagram of a pole piece assembly provided in another embodiment of the present application along the thickness direction of the pole piece assembly;

[0033] Figure 6 is a schematic cross-sectional structural diagram of a pole piece assembly along the thickness direction of the pole piece assembly provided in yet another embodiment of the present application;

[0034] Figure 7 It is a schematic diagram of the top view structure of a pole piece assembly provided in another embodiment of the present application.

[0035] Description of reference numerals:

[0036] 10-composite current collector; 101-second conductive layer; 102-polymer layer; 103-ear portion; 1031-welding area; 104-bearing portion; 20-first conductive layer; 201-main body; 202-extension portion; 30-active material layer; 40-through hole; 50-conductor; 01-first pole piece; 02-diaphragm; 03-second pole piece. DETAILED DESCRIPTION

[0037] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0038] The applicant of the present application has found that the existing composite current collector reduces the amount of metal used by introducing a polymer layer, which significantly reduces the weight of the current collector, thereby increasing the energy density of the secondary battery using the composite current collector by 5% to 10%. However, the composite current collector reduces the amount of metal used by using a polymer layer. Since the metal layer in the composite current collector is thinner, the transmission resistance of electrons in the composite current collector is significantly increased compared to the traditional metal foil current collector, resulting in a secondary battery based on the composite current collector having a larger internal resistance, as well as poor current capacity and rate performance. In addition, since the thickness of the metal layer in the composite current collector is thin, and the two metal layers in the composite current collector are not interconnected, the welding process of the pole piece prepared using the composite current collector is complicated and costly.

[0039] In order to solve the above problems, the present application provides a secondary battery. Figure 1 The secondary battery comprises a pole piece assembly, the pole piece assembly comprises a first pole piece 01, a second pole piece 03 and a diaphragm 02, one of the first pole piece 01 and the second pole piece 03 is a positive pole piece and the other is a negative pole piece, and the diaphragm 02 is used to isolate the first pole piece 01 and the second pole piece 03 to prevent the first pole piece 01 and the second pole piece 03 from contacting and short-circuiting; specifically, the first pole piece 01 comprises a composite current collector 10, a first conductive layer 20, an active material layer 30 and a conductor 50; the composite current collector 10 has a pole ear portion 103 and a load-bearing The pole ear portion 104 is connected to the bearing portion 104, the active material layer 30 is stacked on the bearing portion 104, the first conductive layer 20 is arranged on the same side of the pole ear portion 103 as the active material layer 30, and a part of the first conductive layer 20 is connected to the active material layer 30, and a through hole 40 penetrating the pole ear portion 103 is provided at the end of the pole ear portion 103 away from the bearing portion 104, and the through hole 40 extends along the thickness direction of the pole ear portion 103, the conductor 50 is filled in the through hole 40, and the conductor 50 is connected to the first conductive layer 20.

[0040] In one embodiment, the structure of the second pole piece 03 can be completely the same as that of the first pole piece 01, except that the material composition of the active material layer 30 and the material composition of the composite current collector 10 are different. In one embodiment, the second pole piece 03 can also include a composite current collector 10 and an active material 30, and the composite current collector 10 has a pole ear portion 103 and a bearing portion 104 connected to each other, and the active material layer 30 is stacked on the bearing portion 104.

[0041] exist Figure 1 In the case where the first pole sheet 01 is a positive pole sheet, the active material layer 30 is a positive active material layer, and the composite current collector 10 is a positive composite current collector. In the case where the first pole sheet 01 is a negative pole sheet, the active material layer 30 is a negative active material layer, and the composite current collector 10 is a negative composite current collector.

[0042] The pole ear portion 103 is a region of the composite current collector 10 for connecting with a pole or a transition piece to achieve electron transmission between the active material layer 30 and the pole, and the bearing portion 104 is a region of the composite current collector 10 for bearing the active material layer 30 .

[0043] In one embodiment, the first conductive layer 20 may include a first conductive agent and an adhesive. The first conductive agent includes at least one of conductive carbon black, carbon nanotubes, conductive fibers, graphene, nanosilver, and nanotin. The adhesive may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. In the case where the first conductive layer 20 includes a first conductive agent and an adhesive, the slurry including the first conductive agent and the adhesive can be applied to the surface of the composite current collector 10 by using existing coating technology before the carrier part 104 prepares the active material layer 30, so as to obtain the first conductive layer 20 in which the extension part 202 extends and is embedded between the composite current collector 10 and the active material layer 30; or, after the carrier part 104 prepares the active material layer 30, the slurry including the first conductive agent and the adhesive can be applied to the surfaces of the composite current collector 10 and the active material layer 30 by using existing coating technology, so as to obtain the first conductive layer 20 in which the extension part 202 extends along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and is attached to the active material layer 30. In one embodiment, when the first conductive layer 20 includes a first conductive agent and an adhesive, the content of the first conductive agent in the first conductive layer 20 is 70 wt.% to 95 wt.%, for example, it can be one of 70 wt.%, 75 wt.%, 80 wt.%, 85 wt.%, 90 wt.%, 95 wt.% or any two of the range values.

[0044] In one embodiment, the first conductive layer 20 is a metal layer, and the metal layer is any one of a copper layer, an aluminum layer, an indium gallium tin layer, and a gallium tin alloy layer. In some embodiments, the first conductive layer 20 may also be a metal layer deposited on the surface of the composite current collector 10 by a vapor deposition method before the carrier 104 prepares the active material layer 30, or may be a metal layer deposited on the surface of the active material layer 30 on the surface of the composite current collector 10 by a vapor deposition method after the carrier 104 prepares the active material layer 30, and the metal layer is a metal plating layer with high electrical conductivity.

[0045] In one embodiment, the material of the first conductive layer 20 is the same as that of the active material layer 30 .

[0046] The first conductive layer 20 and the active material layer 30 are arranged on the same side of the pole ear portion 103, and a part of the first conductive layer 10 is connected to the active material layer 30. The part of the first conductive layer 20 may extend and be embedded between the composite current collector 10 and the active material layer 30, or may extend along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and be attached to at least a part of the active material layer 30 near the composite current collector 10, or may extend to between the composite current collector 10 and the active material layer 30 and at least extend along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and be attached to at least a part of the active material layer 30 near the composite current collector 10. The embodiment of the present application does not specifically limit the way in which the part of the first conductive layer 20 is connected to the active material layer 30. By providing the first conductive layer 20 connecting the composite current collector 10 and the active material layer 30, the electron transmission path between the composite current collector 10 and the active material layer 30 is broadened, the transmission speed of electrons between the composite current collector 10 and the electrode tab is accelerated, the electron transmission capacity of the composite current collector 10 is improved, and the rate performance and current carrying capacity of the secondary battery are improved.

[0047] In the embodiment of the present application, the end of the pole ear portion 103 away from the load-bearing portion 104 is the portion connected to the adapter or the pole, and a through hole 40 penetrating the pole ear portion 103 is provided at the end of the pole ear portion 103 away from the load-bearing portion 104, which is used to fill the conductor 50, so as to realize the electrical connection of the pole pieces of the same polarity in the pole piece assembly through the conductor 50, which is beneficial to improve the welding performance and the current carrying capacity. When the pole pieces of the same polarity are connected through the conductor 50, the existing welding technology can be further used to weld the end of the pole ear portion 103 away from the load-bearing portion 104 to the adapter or the pole.

[0048] Among them, the conductor 50 filled in the through hole 40 can be a conductive paste obtained by mixing at least one of highly conductive nanoparticles such as graphene, carbon tubes, nanosilver, nanotin, etc. with an adhesive and then solidifying it, or it can be a liquid metal that is cooled and solidified. The embodiment of the present application does not make specific limitations on this.

[0049] By opening a through hole 40 penetrating the pole ear portion 103 at the end of the pole ear portion 103 away from the bearing portion 104, and filling the through hole 40 with a conductor 50, the welding of pole pieces of the same polarity in the pole piece assembly is achieved through the conductor 50 filled in the through hole 40, thereby reducing the welding difficulty and welding cost between pole pieces based on the composite current collector 10. Furthermore, the first conductive layer 20 arranged in the pole ear portion 103 increases the effective contact area between the conductor 50 filled in the through hole 40 and the composite current collector 10, further reducing the resistance of electron transmission between the active material layer 30 and the pole, while ensuring the energy density of the secondary battery, the rate performance and current carrying capacity of the secondary battery are also improved, and the welding complexity and welding cost between pole pieces in the secondary battery based on the composite current collector 10 are reduced.

[0050] The first conductive layer 20 provided in the embodiment of the present application can be realized by existing coating technologies such as multi-layer coating or multiple coating, edge coating, edge spraying, evaporation, chemical plating, and electroplating; for the through hole 40, the through hole 40 that penetrates the pole ear portion 103 can be opened at the end of the pole ear portion 103 away from the bearing portion 104 by using the existing punching technology, and the conductor 50 filled in the through hole 40 is obtained by pouring a conductive slurry or liquid metal into the through hole 40 and curing it. It can be compatible with the existing preparation process of the secondary battery electrode or the deposition process of the composite current collector, and the preparation process is simple. The secondary battery provided in the embodiment of the present application can be any material chemical system using a composite current collector (for example, the positive electrode active material is selected from the NCM ternary series, the NCA ternary series, lithium iron phosphate, etc., and the negative electrode active material is selected from artificial graphite, natural graphite, lithium titanate, silicon-based negative electrode, etc.), which is suitable for the existing secondary battery material system and other systems using composite current collector pole pieces, and has high practicality and a wide range of applications.

[0051] Reference Figure 1 In one embodiment, the composite current collector 10 includes two second conductive layers 101 and a polymer layer 102 , and two opposite surfaces of the polymer layer 102 are respectively provided with a second conductive layer 101 .

[0052] The sum of the thicknesses of the first conductive layer 20 and the second conductive layer 101 on the same side of the composite current collector 10 is 1.5 μm to 12 μm, for example, it can be one or any two of 1.5 μm, 1.8 μm, 2 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm.

[0053] The second conductive layer 101 may be any one of a metal foil layer, carbon fiber, carbon paper, and carbon nanotube paper (bucky paper), and the polymer layer 102 may be at least one of polyethylene terephthalate (PET), polypropylene (PP), and polyimide (PI).

[0054] The surface of the composite current collector 10 is the surface of the second conductive layer 101 of the composite current collector 10 that faces away from the polymer layer 102 .

[0055] In one embodiment, the thickness of the first conductive layer 20 is 1 μm to 10 μm, for example, it can be in the range of one or any two of 1 μm, 3 μm, 5 μm, 8 μm, and 10 μm.

[0056] Reference Figure 1 In one embodiment, the end of the pole ear portion 103 away from the bearing portion 104 has a welding area, the opening end of the through hole 40 is located in the welding area, and the ratio of the total area of ​​the through hole 40 in the welding area to the total area of ​​the welding area is 1 / 5 to 3 / 5, for example, it can be a range value of one or any two of 1 / 5, 1 / 4, 1 / 3, 1 / 2, 3 / 5. Setting the ratio of the total area of ​​the through hole 40 to the total area of ​​the welding area to 1 / 5 to 3 / 5 can increase the proportion of the conductor 50 in the welding area while ensuring the self-supporting strength of the bearing portion 104, so as to improve the connection strength and contact area between the pole pieces connected by the conductor 50 in the pole piece assembly, thereby facilitating the increase of the transmission speed of electrons between the pole piece and the adapter or pole, and further improving the current carrying capacity of the pole piece.

[0057] The through holes 40 are disposed in the welding area at the end of the pole ear portion 103 away from the bearing portion 104. The total area of ​​the through holes 40 in the welding area is the sum of the areas of the opening ends of the through holes 40 in the welding area.

[0058] Reference Figure 2 A plurality of through holes 40 are provided in the welding area 1031 , and the ratio of the total area of ​​the through holes 40 in the welding area 1031 to the total area of ​​the welding area 1031 is 1 / 5 to 3 / 5.

[0059] In the schematic diagram of the top view of the welding area, the cross-sectional shape of the through hole 40 can be a polygon and Figure 2 The circular or elliptical shape or other shapes shown in the figure are not specifically limited in the embodiment of the present application; the polygon can be any one of a rectangle, a rhombus, a triangle, a hexagon, a pentagon, etc. Specifically, the welding area 1031 can be punched by existing punching technologies such as physical punching and laser punching to obtain the through hole 40.

[0060] In the embodiment of the present application, the top-view shape of the cross-section of the through hole 40 can preferably be a shape with a relatively large perimeter or area, such as a triangle, rectangle, or circle, so as to increase the filling amount of the conductor 50 in the through hole 40, increase the contact area between the conductor 50 and the pole piece, and thereby increase the transmission speed of electrons between each pole piece and the adapter connected by the conductor 50 in the pole piece assembly, thereby improving the current carrying capacity of the pole piece.

[0061] In one embodiment, a plurality of through holes 40 are provided, and in the pole ear portion 103 , the distance between two adjacent through holes 40 is greater than or equal to a target length of the through holes 40 .

[0062] When the cross-section of the through hole 40 is circular in top view, the target length is the diameter of the circle; when the cross-section of the through hole 40 is polygonal in top view, the target length is the length of the shortest side of the polygon.

[0063] In the embodiment of the present application, the distance between two adjacent through holes 40 refers to the shortest distance between the edges of two adjacent through holes 40. The target length of the through hole 40 is the target length of the through hole 40 in the axial direction perpendicular to the through hole 40, and the determination method of the target length varies depending on the top view shape of the cross section of the through hole 40; specifically, when the top view shape of the cross section of the through hole 40 is a circle, the target length is the diameter of the circle; when the top view shape of the cross section of the through hole 40 is a polygon, the target length is the length of the shortest side of the polygon.

[0064] The distance between two adjacent through holes 40 is greater than or equal to the target length of the through holes 40, which can avoid the self-supporting strength of the pole ear portion 103 being too low due to the small distance between the through holes 40 in the pole ear portion 103. While reducing the difficulty of welding the pole piece based on the composite current collector 10, it also ensures the self-supporting strength of the pole ear portion 103 and prevents the deformation of the pole ear portion 103 caused by the opening of the through hole 40 in the pole ear portion 103.

[0065] Reference Figure 1 In one embodiment, the first conductive layer 20 includes a main body portion 201 and an extension portion 202 connected to each other, the main body portion 201 is disposed at the pole ear portion 103 , and the extension portion 202 is connected to the active material layer 30 .

[0066] The main body portion 201 covers the entire surface of the tab portion 103 facing the active material layer 30 .

[0067] When the electrode sheet is cut along the thickness direction of the electrode sheet, the shape of the cross-section of the main body 201 can be as follows: Figure 1 The rectangular structure shown in FIG. 1 is a rectangular structure in which the main body 201 evenly covers the pole ear 103. The cross-sectional shape of the extension 202 may include but is not limited to the following: Figure 1The quadrilateral structure, triangular structure, wedge-shaped structure, etc. shown in the figure. Among them, the quadrilateral structure can be a rectangular structure.

[0068] In the embodiment of the present application, the main body 201 of the first conductive layer 20 is arranged in the pole ear portion 103 of the composite current collector 10, and the extension portion 202 in the first conductive layer 20 connected to the main body 201 is connected to the active material layer 30. The composite current collector 10 is connected to the active material layer 30 through the main body 201 and the extension portion 202 in the first conductive layer 20 that are interconnected, thereby widening the electron transmission path between the composite current collector 10 and the active material layer 30. Furthermore, the main body 201 of the first conductive layer 20 arranged in the pole ear portion 103 increases the effective contact area between the conductor 50 filled in the through hole 40 and the composite current collector 10, further reducing the resistance to the transmission of electrons between the active material layer 30 and the pole, accelerating the speed at which electrons are transmitted between the active material layer 30 and the adapter or pole through the composite current collector 10, and improving the current carrying capacity of the pole piece.

[0069] In addition, since the thickness of the second conductive layer 101 and the polymer layer 102 in the composite current collector 10 are both relatively thin, the self-supporting strength of the entire composite current collector 10 is relatively weak, and it is easy to fold or curl. In the embodiment of the present application, the first conductive layer 20 is arranged on the composite current collector 10, which can also improve the self-supporting strength of the composite current collector 10 and prevent the occurrence of folding or curling of the pole ear portion in the composite current collector 10.

[0070] Reference Figure 1 In one embodiment, the extension portion 202 extends from the main body 201 to the bearing portion 104 along the direction from the pole ear portion 103 to the bearing portion 104 to connect with the active material layer 30. The length of the extension portion 202 extending and embedded between the composite current collector 10 and the active material layer 30 is greater than 0 and is less than the length of the bearing portion 104 along the direction from the pole ear portion 103 to the bearing portion 104.

[0071] Reference Figure 3 The pole piece includes an active material layer 30 disposed on the bearing portion 104 and a main body 201 of the first conductive layer 20 disposed on the pole ear portion 103. It can be understood that when the extension portion 202 extends from the main body 201 to the bearing portion 104 along the direction from the pole ear portion 103 to the bearing portion 104 to connect with the active material layer 30, the extension portion 202 is covered by the active material layer 30.

[0072] Reference Figure 4 In one embodiment, the extension portion 202 in the first conductive layer 20 extends from the main body portion 201 to the bearing portion 104 along the direction from the pole ear portion 103 to the bearing portion 104 to be connected to the active material layer 30, and the pole piece is cut along the thickness direction of the pole piece, and the shape of the cross-sectional surface of the extension portion 202 is a wedge-shaped structure.

[0073] In the implementation of the present application, the extension portion 202 of the first conductive layer 20 extends from the main body 201 to the bearing portion 104 along the direction from the pole ear portion 103 to the bearing portion 104 to connect with the active material layer 30. Specifically, before preparing the active material layer 30 on the composite current collector 10, the first conductive layer 20 can be first prepared on the surface of the composite current collector 10, and after the first conductive layer 20 is prepared, the active material layer 30 is prepared in the composite current collector 10, and a part of the active material layer 30 is directly stacked on the area of ​​the composite current collector 10 not covered by the first conductive layer 20, and the remaining part is extended and stacked to the local surface of the first conductive layer 20, so that the local extension of the active material layer 30 covers the local first conductive layer 20, and a pole piece including the composite current collector 10, the first conductive layer 20, and the active material layer 30 is obtained. In this way, the main body 201 and the extension part 202 in the first conductive layer 20 can be prepared by at least one of the existing coating technology, spraying technology, evaporation technology, chemical plating technology, and electroplating technology. The process is simple and easy to implement.

[0074] When the extension portion 202 extends from the main body 201 to the bearing portion 104 along the direction from the pole ear portion 103 to the bearing portion 104 to connect with the active material layer 30, the extension track length from the end of the extension portion 102 away from the main body 201 to the end connected with the main body 201 is less than the length of the bearing portion 104 along the direction from the pole ear portion 103 to the bearing portion 104. In this way, while the composite current collector 10 and the active material layer 30 are connected through the extension portion 104, the space occupied by the extension portion 202 in the active material layer 30 is reduced, and while the electron transmission or current transmission capacity of the composite current collector 10 is improved, the energy density loss of the secondary battery is small.

[0075] Reference Figure 4 In one embodiment, the extension portion 202 has a first side and a second side, the first side is the connection side of the extension portion 202 with the main body portion 201, and the second side is the side of the extension portion 202 away from the connection side; the thickness of the extension portion 202 near the first side is greater than or equal to the thickness of the extension portion 202 near the second side. In the case where the extension portion 202 extends along the direction from the pole ear portion 103 to the bearing portion 104 and is attached to the surface of the composite current collector 10, the first thickness of the extension portion 202 near the first side is greater than or equal to the second thickness of the extension portion 202 near the second side. While ensuring that the composite current collector 10 and the active material layer 30 are connected through the extension portion 202, the space occupied by the extension portion 202 in the active material layer 30 is reduced, and while improving the electron transmission capacity of the composite current collector 10, the proportion of the extension portion 202 is reduced, so that the energy density loss of the secondary battery is small.

[0076] Reference Figure 5 , Figure 6 In one embodiment, the extension portion 202 extends along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and is attached to the active material layer 30 .

[0077] In the embodiment of the present application, the extension portion 202 may extend in a direction away from the composite current collector 10 along the thickness direction of the composite current collector 10 and be attached to a surface of the active material layer 30 facing the electrode lug portion 103 .

[0078] In one embodiment, the extension portion 202 may be attached to the entire surface of the active material layer 30 facing the pole ear portion 103. In one embodiment, the extension portion 202 may also be attached to only a portion of the surface of the active material layer 30 facing the pole ear portion 103 and close to the composite current collector 10. In one embodiment, the end of the extension portion 202 away from the main body 201 may also extend to cover a local area of ​​the surface of the active material layer 30 facing away from the composite current collector 10. The specific area of ​​the extension portion 202 extending and attached to the active material layer 30 is not specifically limited in the embodiment of the present application. It should be noted that, in the case where one end of the extension portion 202 away from the main body portion 201 extends to cover a local area of ​​the surface of the active material layer 30 facing away from the composite current collector 10, the length of the portion of the extension portion 202 extending to cover a local area of ​​the surface of the active material layer 30 facing away from the composite current collector 10 along the direction from the pole ear portion 103 to the bearing portion 104 is greater than 0 and less than the length of the surface of the active material layer 30 facing away from the composite current collector 10 along the direction from the pole ear portion 103 to the bearing portion 104.

[0079] The active material layer 30 has an inclined surface, which is used to attach the extension portion 202 of the first conductive layer 20. The inclined surface can be a plane intersecting with the plane where the composite current collector 10 extends, or a curved surface intersecting with the plane where the composite current collector 10 extends.

[0080] For example, the surface of the active material layer 30 facing the pole ear portion 103 can be thinned by existing thinning technology to obtain an inclined surface, and the extension portion 202 attached to the active material layer 30 is prepared on the inclined surface, and the main body 201 connected to the extension portion 202 is prepared on the surface of the pole ear portion 103 facing the active material layer 30, and then the first conductive layer 20 connecting the composite current collector 10 and the active material layer 30 can be obtained. In the embodiment of the present application, the surface of the active material layer 30 facing the pole ear portion 103 is prepared as an inclined surface, which is conducive to the subsequent preparation of the extension portion 202 and improves the operability of preparing the extension portion 202.

[0081] Reference Figure 7 , showing that this application Figure 5 or Figure 6The schematic diagram of the top view structure of the pole piece shown, the pole piece includes an active material layer 30 disposed on the upper surface of the bearing portion 104, and a main body 201 of the first conductive layer 20 disposed on the upper surface of the pole ear portion 103, and an extension portion 202 extending along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and attached to the active material layer 30. When the extension portion 202 extends along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and is attached to the active material layer 30, and the surface of the active material layer 30 facing the pole ear portion 103 is an inclined surface, the main body 201 and the extension portion 202 of the first conductive layer 20 can be observed at the same time in the top view structure diagram of the pole piece.

[0082] In the implementation of the present application, the extension portion 202 of the first conductive layer 20 extends along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and is attached to the active material layer 30, so as to realize the connection between the extension portion 202 and the active material layer 30. Specifically, after the active material layer 30 is prepared on the surface of the composite current collector 10, at least one of the existing coating technology, spraying technology, evaporation technology, chemical plating technology, and electroplating technology can be used to prepare the main body 201 of the first conductive layer 20 on the pole ear portion 103 of the composite current collector 10, and the extension portion 202 extending along the thickness direction of the composite current collector 10 in a direction away from the composite current collector 10 and attached to the active material layer 30 is prepared on the surface of the active material layer 30 facing the pole ear portion 103, so as to obtain a pole piece including the composite current collector 10, the first conductive layer 20, and the active material layer 30. In this way, the preparation of the first conductive layer 20 can be realized by existing coating, spraying, evaporation, chemical plating, electroplating and other technologies, and the process is simple and easy to implement.

[0083] Reference Figure 4 In one embodiment, the length of the extension track from one end of the extension portion 202 away from the main body portion 201 to one end connected to the main body portion 201 is 1 mm to 10 mm, for example, it can be one of 1 mm, 3 mm, 6 mm, 10 mm or any two of the range values. The length of the extension track from one end of the main body portion 201 away from the extension portion 202 to one end connected to the extension portion 202 is 10 mm to 50 mm, for example, it can be one of 10 mm, 20 mm, 30 mm, 40 mm, 50 mm or any two of the range values.

[0084] In some embodiments, when the positive electrode sheet of the secondary battery includes a composite current collector 10, a first conductive layer 20, an active material layer 30 and a conductor 50, the composite current collector 10 is a positive composite current collector, and the active material layer 20 is a positive active material layer. The positive active material layer includes a positive active material, a second conductive agent and a binder. Among them, the positive active material may include but is not limited to a ternary material (such as LiNi 0.8 Mn0.1 Co 0.1 O2, NMC811; or NMC622; or NMC523; or LiNi 0.8 Co 0.15 Al 0.05 O2, NCA, etc.), lithium iron phosphate (LiFePO4, LFP), etc. The second conductive agent may include at least one of conductive carbon black, acetylene black (Super P), Ketjen black, carbon nanotubes, and graphene. The adhesive may include at least one of polyvinylidene fluoride, polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and tetrafluoroethylene-hexafluoropropylene copolymer. The first conductive layer 20 may include a first conductive agent and an adhesive, or may include a pure metal with high conductivity, or may include the same components as the positive electrode active material layer. The conductor 50 may be obtained by curing a conductive paste including an adhesive and at least one of highly conductive nanoparticles such as graphene, carbon tubes, nanosilver, and nanotin, or may be obtained by curing a liquid metal.

[0085] In some embodiments, when the negative electrode sheet of the secondary battery includes a composite current collector 10, a first conductive layer 20, an active material layer 30 and a conductor 50, the composite current collector 10 is a negative composite current collector, and the active material layer 20 is a negative active material layer. The negative active material layer includes a negative active material, a second conductive agent and a binder. Among them, the negative active material may include but is not limited to artificial graphite (AG), natural graphite (NG), lithium titanate (Li4Ti5O 12 ) etc. The conductor 50 may be obtained by curing a conductive paste including an adhesive and at least one of highly conductive nanoparticles such as graphene, carbon tubes, nanosilver, and nanotin, or may be obtained by curing a liquid metal. The adhesive is a commonly used adhesive for the negative electrode of a secondary battery, and will not be described in detail here.

[0086] In some embodiments, the positive electrode sheet and the negative electrode sheet of the secondary battery both include a composite current collector 10, a first conductive layer 20, an active material layer 30 and a conductor 50, wherein the composite current collector 10 in the positive electrode sheet is a positive electrode composite current collector, and the active material layer 30 in the positive electrode sheet is a positive electrode active material layer; the composite current collector 10 in the negative electrode sheet is a negative electrode composite current collector, and the active material layer 30 in the negative electrode sheet is a negative electrode active material layer.

[0087] The secondary battery provided in the embodiment of the present application also includes an electrolyte.

[0088] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode. In some embodiments, the electrolyte is a liquid electrolyte, which includes an electrolyte salt and a solvent, and the electrolyte salt is a lithium salt, which is commonly used in secondary batteries and will not be described in detail here.

[0089] In practical applications, the prepared positive electrode sheet, separator 02, and negative electrode sheet are stacked in order so that the separator 02 is located between the positive and negative electrode sheets; the end of the pole ear portion 103 in the composite current collector 10 of at least one of the positive electrode sheet and the negative electrode sheet away from the bearing portion 104 is punched to obtain a through hole 40 that penetrates the pole ear portion 103, and a conductive slurry or liquid metal is poured into the through hole 40, and after curing, a conductor 50 filled in the through hole 40 is obtained, and the conductor 50 is connected to the first conductive layer 20; the pole ear portion 103 of the positive electrode sheet and the pole ear portion 103 of the negative electrode sheet are welded respectively using the existing welding process to obtain a bare cell; finally, the bare cell is shelled, and after baking, liquid injection, formation, secondary sealing, and sorting are performed to obtain the above-mentioned secondary battery.

[0090] An embodiment of the present application further provides an electric device, which includes the secondary battery as described above, and the secondary battery serves as a power supply for the electric device.

[0091] In order to make the invention purpose, technical solution and beneficial effects of the present application clearer, the present application is further described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present application and are not used to limit the scope of the present application.

[0092] Test method:

[0093] (1) Room temperature DCR test: At 25±2°C, charge at 1C to 4.25V (ternary positive electrode / / graphite negative electrode system, other secondary battery systems can be set according to the conventional voltage), discharge at 1C to 50% SOC, and then discharge at 3C constant current pulse for 10s; calculate DCR = (voltage before pulse discharge - voltage after pulse discharge) / discharge current.

[0094] (2) Room temperature rate performance test: At 25±2°C, perform charge and discharge cycle tests at charge and discharge rates of 0.33C / 0.33C and 4C / 4C in the range of 2.8V to 4.25V (ternary positive electrode / / graphite negative electrode system, other secondary battery systems can be set at conventional voltages) for 5 cycles each, and record the average capacity at each current density. For example, the average capacity at a current density of 0.33C / 0.33C is recorded as Q 0.33C . Rate performance at 4C current = Q 4C / Q 0.33C *100%.

[0095] (3) Temperature rise test of the composite current collector side tab: In the room temperature rate performance test, the first cycle of 4C / 4C charge and discharge is measured. Specifically, the temperature difference of the composite current collector side tab is recorded during the process of charging to 4.25V at 4C and leaving it for 15 minutes, and then discharging to 2.5V at 4C.

[0096] Example 1

[0097] (1) Preparation of positive electrode slurry:

[0098] The positive electrode active material LiNi 0.8 Mn 0.1 Co 0.1 O2, the second conductive agent acetylene black and the binder polyvinylidene fluoride are evenly mixed in a mass ratio of 95:3:2, and evenly dispersed in 1-methyl-2-pyrrolidone to prepare a uniform positive electrode slurry.

[0099] (2) Preparation of negative electrode slurry:

[0100] The negative electrode active material artificial graphite, the second conductive agent acetylene black and the binder styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were mixed evenly in a mass ratio of 95:2:1.5:1.5, and evenly dispersed in deionized water to prepare a uniform negative electrode slurry.

[0101] (3) Preparation of conductive paste corresponding to the first conductive layer and the conductor:

[0102] The first conductive agent nano silver powder and the adhesive polyvinylidene fluoride are uniformly mixed in a mass ratio of 90:10 to obtain a conductive paste corresponding to the first conductive layer, and the conductive paste is also a conductive paste corresponding to the conductor.

[0103] (4) Preparation of positive electrode sheet:

[0104] An aluminum foil composite current collector is used as a positive electrode current collector, and the positive electrode slurry is coated on the two surfaces of the aluminum foil composite current collector respectively by using the existing coating technology, and the positive electrode active material layer is obtained after drying; the conductive slurry is coated on the surface on the same side as the positive electrode active material layer in the pole ear part of the aluminum foil composite current collector, the surface facing the pole ear part in the positive electrode active material layer, and the local surface of the positive electrode active material layer facing away from the aluminum foil composite current collector by using the existing coating technology, and the first conductive layer is obtained after drying; after rolling, die cutting and other processes, the positive electrode sheet is obtained.

[0105] Among them, the main body of the first conductive layer is arranged at the pole ear part, and the extension part connected to the main body part extends along the thickness direction of the aluminum foil composite current collector in the direction away from the aluminum foil composite current collector and is attached to the positive electrode active material layer; the extension track length from one end of the extension part away from the main body part to the end connected to the main body part is 1mm; the thickness of the first conductive layer is 1μm; the aluminum foil composite current collector includes two aluminum layers with a thickness of 1μm respectively and a PET layer with a thickness of 6μm arranged between the two aluminum layers.

[0106] (5) Preparation of negative electrode sheet:

[0107] A copper foil composite current collector is used as a negative electrode current collector, and negative electrode slurry is coated on two surfaces of the copper foil composite current collector by using existing coating technology, and a negative electrode active material layer is obtained after drying; a conductive slurry is coated on the surface on the same side as the negative electrode active material layer in the pole ear portion of the copper foil composite current collector, the surface facing the pole ear portion in the negative electrode active material layer, and the local surface of the negative electrode active material layer facing away from the copper foil composite current collector by using existing coating technology, and a first conductive layer is obtained after drying; after processes such as rolling and die cutting, a negative electrode sheet is obtained.

[0108] Among them, the main body of the first conductive layer is arranged on the pole ear part, and the extension part connected to the main body part extends along the thickness direction of the copper foil composite current collector in the direction away from the copper foil composite current collector and is attached to the negative electrode active material layer; the extension track length from one end of the extension part away from the main body part to the end connected to the main body part is 1mm; the thickness of the first conductive layer is 1μm; the copper foil composite current collector includes two copper layers with a thickness of 0.8μm respectively and a PET layer with a thickness of 4μm arranged between the two copper layers.

[0109] (6) Preparation of secondary batteries:

[0110] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is located between the positive and negative electrode sheets, and the ends of the pole ear portions of the composite current collectors of the positive electrode sheet and the negative electrode sheet away from the bearing portion are punched to obtain through holes penetrating the pole ear portions, and the conductive slurry obtained in step (3) is poured into the through holes, and after curing, the conductor filled in the through holes is obtained; the pole ear portions of the positive electrode sheet and the pole ear portions of the negative electrode sheet are welded respectively by the existing welding process to obtain a bare battery, and the bare secondary battery is placed in an outer packaging aluminum plastic film, and placed in an oven at 85±10°C for baking for 24 hours, and the electrolyte is injected into the dried secondary battery, and the electrolyte is allowed to stand, formed, and divided to complete the preparation of the lithium ion soft pack secondary battery. Wherein, the separator is a PE film, the electrolyte contains 1M LiPF6, and the solvent of the electrolyte includes EC (ethylene carbonate), PC (propylene carbonate) and EMC (ethyl methyl carbonate), and the volume ratio of EC, PC and EMC is 1:1:1.

[0111] The top view cross-section of the through hole is circular; the area of ​​the through hole in the welding area = π*1mm*1mm*12 = 37.68mm 2 ; The area of ​​the welding area is 24mm (ear width) * 8mm (welding area length) = 192mm 2 The ratio of the total area of ​​the through holes in the welding region to the total area of ​​the welding region at the end of the pole ear away from the bearing portion is approximately 1 / 5; the distance between two adjacent through holes is equal to the diameter of the through holes.

[0112] Example 2

[0113] The difference between Example 2 and Example 1 is that in step (4), the thickness of the first conductive layer is 5 μm.

[0114] Example 3

[0115] The difference between Example 3 and Example 1 is that in step (4), the thickness of the first conductive layer is 10 μm, and the thickness of the aluminum layer in the aluminum foil composite current collector is 2 μm.

[0116] Example 4

[0117] The difference between Example 4 and Example 1 is that in step (4), the positive electrode current collector is an aluminum foil current collector, and the thickness of the aluminum foil current collector is 12 μm;

[0118] In step (6), the operation of punching the end of the pole ear portion of the positive electrode sheet current collector away from the bearing portion to obtain a through hole penetrating the pole ear portion, and pouring conductive slurry into the through hole to obtain a conductor filled in the through hole after curing is not performed.

[0119] Example 5

[0120] The difference between Example 5 and Example 1 is that in step (5), the negative electrode current collector is a copper foil current collector, and the thickness of the copper foil current collector is 6 μm;

[0121] In step (6), the operation of punching the end of the pole ear portion of the negative electrode sheet current collector away from the supporting portion to obtain a through hole penetrating the pole ear portion, and pouring conductive slurry into the through hole to obtain a conductor filled in the through hole after curing is not performed.

[0122] Example 6

[0123] The difference between Example 6 and Example 1 is that in step (6), the ratio of the total area of ​​the through holes in the welding region to the total area of ​​the welding area at the end of the pole ear away from the bearing portion is approximately 3 / 5.

[0124] Example 7

[0125] The difference between Example 7 and Example 1 is that in step (6), the ratio of the total area of ​​the through holes in the welding region to the total area of ​​the welding area at the end of the pole ear away from the bearing portion is approximately 2 / 5.

[0126] Example 8

[0127] The difference between Example 8 and Example 1 is that, in step (6), the distance between two adjacent through holes is greater than the diameter of the through holes.

[0128] Example 9

[0129] The difference between Example 9 and Example 1 is that in step (6), the top-view cross-section of the through hole is a square, and the distance between two adjacent through holes is equal to the side length of the through hole.

[0130] Example 10

[0131] The difference between Example 10 and Example 9 is that, in step (6), the distance between two adjacent through holes is greater than the side length of the through holes.

[0132] Embodiment 11

[0133] The difference between Example 11 and Example 1 is that in step (6), the top-view cross-section of the through hole is in the shape of a rhombus, and the distance between two adjacent through holes is equal to the length of the shortest side of the through hole.

[0134] Example 12

[0135] The difference between Example 12 and Example 1 is that in step (6), after the ends of the pole ear portions in the composite current collector of the positive electrode sheet and the negative electrode sheet away from the bearing portion are punched respectively to obtain through holes penetrating the pole ear portions, liquid metal is poured into the through holes, and after solidification, a conductor filled in the through holes is obtained; wherein the pouring temperature of the liquid metal is 120°C.

[0136] Embodiment 13

[0137] The difference between Example 13 and Example 12 is that in step (4) and step (5), the length of the extension track from the end of the extension portion away from the main body portion to the end connected to the main body portion is 6 mm.

[0138] Embodiment 14

[0139] The difference between Example 14 and Example 1 is that in step (4) and step (5), the length of the extension track from the end of the extension portion away from the main body portion to the end connected to the main body portion is 10 mm.

[0140] Embodiment 15

[0141] The difference between Example 15 and Example 1 is that:

[0142] In step (4), firstly, a conductive paste is applied to the two surfaces of the pole ear of the aluminum foil composite current collector and the local area connected to the pole ear among the two surfaces of the bearing part by using the existing coating technology, and a first conductive layer is obtained after drying; then, a positive electrode paste is applied to the surface of the aluminum foil composite current collector prepared with the first conductive layer by using the existing coating technology, and a positive electrode active material layer is obtained after drying; wherein, the extension part in the first conductive layer extends from the main body part along the direction from the pole ear to the bearing part to the bearing part and is connected to the positive electrode active material layer; the cross-sectional shape of the extension part is a triangular structure; the extension track length from one end of the extension part away from the main body part to one end connected to the main body part is less than the length of the bearing part along the direction from the pole ear part to the bearing part;

[0143] In step (5), firstly, a conductive paste is applied on the two surfaces of the pole ear portion of the copper foil composite current collector and the local areas of the two surfaces of the bearing portion connected to the pole ear portion by using the existing coating technology, and a first conductive layer is obtained after drying; then, a negative electrode paste is applied on the surface of the copper foil composite current collector prepared with the first conductive layer by using the existing coating technology, and a negative electrode active material layer is obtained after drying; wherein, the extension portion in the first conductive layer extends from the main body portion along the direction from the pole ear portion to the bearing portion to the bearing portion and is connected to the negative electrode active material layer; the cross-sectional shape of the extension portion is a triangular structure; and the extension track length from one end of the extension portion away from the main body portion to one end connected to the main body portion is less than the length of the bearing portion along the direction from the pole ear portion to the bearing portion.

[0144] Example 16

[0145] The difference between Example 16 and Example 15 is that the cross-sectional shape of the extension portion in the first conductive layer is a rectangular structure.

[0146] Embodiment 17

[0147] The difference between Example 17 and Example 15 is that the cross-section of the extension portion in the first conductive layer has a wedge-shaped structure.

[0148] Embodiment 18

[0149] The difference between Example 18 and Example 1 is that in step (3), the mass ratio of the first conductive agent nano silver powder to the adhesive polyvinylidene fluoride is 70:30.

[0150] Embodiment 19

[0151] The difference between Example 19 and Example 1 is that in step (3), the mass ratio of the first conductive agent nano silver powder to the adhesive polyvinylidene fluoride is 95:5.

[0152] Embodiment 20

[0153] The difference between Example 20 and Example 18 is that in step (3), the first conductive agent is carbon nanotubes.

[0154] Embodiment 21

[0155] The difference between Example 21 and Example 18 is that in step (3), the first conductive agent is graphene.

[0156] Embodiment 22

[0157] The difference between Example 22 and Example 18 is that in step (3), the first conductive agent includes graphene, carbon nanotubes and adhesive polyvinylidene fluoride, wherein the mass ratio of graphene, carbon nanotubes and adhesive polyvinylidene fluoride is 35:35:30.

[0158] Embodiment 23

[0159] The difference between Example 23 and Example 2 is that in step (3), the conductive paste corresponding to the first conductive layer in the positive electrode sheet is the positive electrode paste; and the conductive paste corresponding to the first conductive layer in the negative electrode sheet is the negative electrode paste.

[0160] Embodiment 24

[0161] The difference between Example 24 and Example 1 is that:

[0162] Step (3) is not included;

[0163] In step (4), after obtaining the positive electrode active material layer, an aluminum layer is deposited by evaporation on the surface of the pole ear portion of the aluminum foil composite current collector on the same side as the positive electrode active material layer, the surface of the positive electrode active material layer facing the pole ear portion, and the partial surface of the positive electrode active material layer facing away from the aluminum foil composite current collector to obtain a first conductive layer;

[0164] In step (5), after obtaining the negative electrode active material layer, a copper layer is deposited by evaporation on the surface of the ear portion of the copper foil composite current collector on the same side as the negative electrode active material layer, as well as on the surface of the negative electrode active material layer facing the ear portion and on the local surface of the negative electrode active material layer facing away from the copper foil composite current collector to obtain a first conductive layer.

[0165] Embodiment 25

[0166] The difference between Example 25 and Example 15 is that:

[0167] Step (3) is not included;

[0168] Before step (4), an aluminum layer is deposited on the two surfaces of the pole ear portion of the aluminum foil composite current collector and the local area of ​​the two surfaces of the support portion connected to the pole ear portion by a vapor deposition method to obtain a first conductive layer;

[0169] Before step (5), a copper layer is deposited on the two surfaces of the copper foil composite current collector pole ear portion and the local area of ​​the two surfaces of the bearing portion connected to the pole ear portion by an evaporation method to obtain a first conductive layer.

[0170] Embodiment 26

[0171] The difference between Example 26 and Example 4 is that in step (4), the positive electrode sheet does not include the first conductive layer;

[0172] In step (5), the thickness of the first conductive layer is 2.5 μm;

[0173] In step (6), the top cross-section of the through hole is square; the ratio of the total area of ​​the through hole in the welding region to the total area of ​​the welding area at the end of the pole ear away from the bearing portion is approximately 1 / 2.

[0174] Embodiment 27

[0175] The difference between Example 27 and Example 5 is that in step (4), the thickness of the first conductive layer is 2 μm;

[0176] In step (5), the negative electrode sheet does not include a first conductive layer;

[0177] In step (6), the ratio of the total area of ​​the through holes in the welding region to the total area of ​​the welding region at the end of the pole ear portion away from the bearing portion is approximately 2 / 5.

[0178] Embodiment 28

[0179] The difference between Example 28 and Example 1 is that in step (4), the thickness of the first conductive layer is 1.5 μm; the thickness of the aluminum layer in the aluminum foil composite current collector is 1.2 μm;

[0180] In step (5), the thickness of the first conductive layer is 3 μm; the thickness of the copper layer in the copper foil composite current collector is 1 μm;

[0181] In step (6), in the composite current collector of the positive electrode sheet, the top-view cross-section of the through hole is in the shape of a triangle, and the ratio of the total area of ​​the through hole to the total area of ​​the welding zone at the end of the pole ear away from the bearing portion is 3 / 5; in the composite current collector of the negative electrode sheet, the ratio of the total area of ​​the through hole in the welding area to the total area of ​​the welding zone at the end of the pole ear away from the bearing portion is approximately 2 / 5.

[0182] Comparative Example 1

[0183] The difference between Comparative Example 1 and Example 27 is that both the positive electrode sheet and the negative electrode sheet do not include the first conductive layer.

[0184] Comparative Example 2

[0185] The difference between Comparative Example 2 and Example 26 is that both the positive electrode sheet and the negative electrode sheet do not include the first conductive layer.

[0186] Comparative Example 3

[0187] The difference between Comparative Example 3 and Example 28 is that both the positive electrode sheet and the negative electrode sheet do not include the first conductive layer.

[0188] The secondary batteries prepared in each embodiment were subjected to room temperature DCR test, room temperature rate test and lug side temperature rise performance test. The test data are shown in Table 1.

[0189] Table 1

[0190] Example Temperature rise of the tab on the composite current collector side / ℃ Internal resistance / mΩ 4C rate performance / % Example 1 3.7 (positive electrode), 2.5 (negative electrode) 4.81 61.02％ Example 2 3.2 (positive electrode), 2.1 (negative electrode) 4.57 64.60％ Example 3 2.8 (positive electrode), 1.8 (negative electrode) 4.12 67.11％ Example 4 2.6 (negative electrode) 4.51 66.11％ Example 5 3.5 (positive electrode) 4.32 63.01％ Example 6 2.7 (positive electrode), 2.0 (negative electrode) 3.81 67.09％ Example 7 3.1 (positive electrode), 2.2 (negative electrode) 4.21 64.32％ Example 8 3.6 (positive electrode), 2.6 (negative electrode) 4.84 61.21％ Example 9 3.6 (positive electrode), 2.4 (negative electrode) 4.59 61.92％ Example 10 3.5 (positive electrode), 2.4 (negative electrode) 4.51 62.78％ Embodiment 11 3.5 (positive electrode), 2.5 (negative electrode) 4.61 61.85％ Example 12 3.3 (positive electrode), 2.2 (negative electrode) 4.01 65.05％ Embodiment 13 2.7 (positive electrode), 2.0 (negative electrode) 3.75 68.33％ Embodiment 14 2.9 (positive electrode), 1.9 (negative electrode) 4.15 67.01％ Embodiment 15 3.7 (positive electrode), 2.6 (negative electrode) 4.83 61.01％ Example 16 3.8 (positive electrode), 2.5 (negative electrode) 4.75 61.31％ Embodiment 17 3.8 (positive electrode), 2.6 (negative electrode) 4.87 60.39％ Embodiment 18 3.8 (positive electrode), 2.9 (negative electrode) 4.97 59.26％ Embodiment 19 3.5 (positive electrode), 2.4 (negative electrode) 4.51 63.03％ Embodiment 20 3.9 (positive electrode), 2.8 (negative electrode) 4.67 61.15％ Embodiment 21 3.7 (positive electrode), 2.7 (negative electrode) 4.45 61.99％ Embodiment 22 3.8 (positive electrode), 2.8 (negative electrode) 4.71 61.82％ Embodiment 23 4.6 (positive electrode), 3.3 (negative electrode) 5.81 47.93％ Embodiment 24 3.1 (positive electrode), 1.9 (negative electrode) 3.97 67.02％ Embodiment 25 3.0 (positive electrode), 1.8 (negative electrode) 3.75 69.92％ Embodiment 26 1.3 (negative electrode) 3.15 70.10％ Embodiment 27 2.0 (positive) 3.04 72.10％ Embodiment 28 2.4 (positive electrode), 1.4 (negative electrode) 3.57 67.90％ Comparative Example 1 5.5 (positive electrode) 5.27 54.80％ Comparative Example 2 3.4 (negative electrode) 5.66 52.60％ Comparative Example 3 5.1 (positive electrode), 3.3 (negative electrode) 5.46 47.30％

[0191] According to the above test data, by comparing Comparative Example 1 and Example 27, it can be seen that by introducing the first conductive layer into the positive electrode sheet based on the composite current collector, the charge and discharge temperature difference of the positive electrode sheet can be reduced from 5.5°C in Comparative Example 1 to 2°C in Example 27, the internal resistance of the secondary battery can be reduced from 5.27mΩ in Comparative Example 1 to 3.04mΩ in Example 27, and the 4C rate performance of the secondary battery can be improved from 54.8% in Comparative Example 1 to 72.1% in Example 27.

[0192] By comparing Comparative Example 2 and Example 26, it can be seen that by introducing the first conductive layer into the negative electrode sheet based on the composite current collector, the charge and discharge temperature difference of the negative electrode sheet can be reduced from 3.4°C in Comparative Example 2 to 1.3°C in Example 26, the internal resistance of the secondary battery can be reduced from 5.66mΩ in Comparative Example 2 to 3.15mΩ in Example 26, and the 4C rate performance of the secondary battery can be improved from 52.6% in Comparative Example 2 to 70.1% in Example 26.

[0193] By comparing Comparative Example 3 and Example 28, it can be seen that by introducing the first conductive layer into the positive and negative electrode sheets based on the composite current collector, the charge and discharge temperature difference of the positive electrode sheet can be reduced from 5.1°C in Comparative Example 3 to 2.4°C in Example 28, and the charge and discharge temperature difference of the negative electrode sheet can be reduced from 3.3°C in Comparative Example 3 to 1.4°C in Example 28; the internal resistance of the secondary battery is reduced from 5.46mΩ in Comparative Example 3 to 3.57mΩ in Example 28, and the 4C rate performance of the secondary battery is improved from 47.3% in Comparative Example 3 to 67.9% in Example 28.

[0194] Comparison of Examples 1-3 and Examples 5-25 with Comparative Examples 1 to 3 shows that the examples all show a small charge and discharge temperature difference of the positive electrode sheet and a small charge and discharge temperature difference of the negative electrode sheet, and at the same time, the internal resistance is relatively small, and the 4C rate performance is greatly improved.

[0195] In summary, the secondary battery provided in the embodiment of the present application, by introducing a first conductive layer and a conductor into the electrode piece, while ensuring the energy density of the secondary battery, also improves the rate performance and current carrying capacity of the secondary battery, and reduces the welding complexity and welding cost between the electrode pieces in the secondary battery based on the composite current collector.

[0196] The above is a detailed introduction to a secondary battery and an electrical device provided by the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method and core idea of ​​the present application. At the same time, for a person skilled in the art, according to the idea of ​​the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A secondary battery, comprising a pole piece assembly, wherein the pole piece assembly comprises a first pole piece (01), a second pole piece (03) and a diaphragm (02) for isolating the first pole piece (01) and the second pole piece (03), wherein one of the first pole piece (01) and the second pole piece (03) is a positive pole piece and the other is a negative pole piece, characterized in that: At least one of the first pole piece (01) and the second pole piece (03) comprises a composite current collector (10), a first conductive layer (20), an active material layer (30) and a conductor (50); The composite current collector (10) comprises a pole ear portion (103) and a bearing portion (104), wherein the pole ear portion (103) is connected to the bearing portion (104); The active material layer (30) is stacked on the supporting portion (104); The first conductive layer (20) and the active material layer (30) are arranged on the same side of the electrode ear portion (103), and a part of the first conductive layer (20) is connected to the active material layer (30); A through hole (40) penetrating the pole ear portion (103) is provided at the end of the pole ear portion (103) away from the bearing portion (104), and the through hole (40) is extended along the thickness direction of the pole ear portion (103); The conductor (50) is filled in the through hole (40) and connected to the first conductive layer (20).

2. The secondary battery according to claim 1, characterized in that: The composite current collector (10) comprises two second conductive layers (101) and a polymer layer (102); the second conductive layer (101) is disposed on two opposite surfaces of the polymer layer (102); The sum of the thicknesses of the first conductive layer (20) and the second conductive layer (101) on the same side of the composite current collector (10) is 1.5 μm to 12 μm.

3. The secondary battery according to claim 1, characterized in that: The thickness of the first conductive layer (20) is 1 μm to 10 μm.

4. The secondary battery according to claim 1, characterized in that: The end of the pole ear portion (103) away from the bearing portion (104) has a welding area, the opening end of the through hole (40) is located in the welding area, and the ratio of the total area of ​​the through hole (40) in the welding area to the total area of ​​the welding area is 1 / 5 to 3 / 5.

5. The secondary battery according to claim 1, characterized in that: A plurality of through holes (40) are provided, and in the pole ear portion (103), a distance between two adjacent through holes (40) is greater than or equal to a target length of the through holes (40); Wherein, when the through hole (40) is circular, the target length is the diameter of the circle; when the through hole (40) is polygonal, the target length is the length of the shortest side in the polygon.

6. The secondary battery according to claim 1, characterized in that: The first conductive layer (20) comprises a main body portion (201) and an extension portion (202) which are connected to each other, the main body portion (201) is arranged on the pole ear portion (103), and the extension portion (202) is connected to the active material layer (30).

7. The secondary battery according to claim 6, characterized in that: The extension portion (202) extends from the main body portion (201) to the bearing portion (104) along a direction from the pole ear portion (103) to the bearing portion (104) to be connected to the active material layer (30).

8. The secondary battery according to claim 6, characterized in that: The extension portion (202) has a first side and a second side, the first side being a side of the extension portion (202) connected to the main body portion (201), and the second side being a side of the extension portion (202) away from the connecting side; In the extension portion (202), a thickness of the extension portion (202) close to the first side is greater than or equal to a thickness of the extension portion (202) close to the second side.

9. The secondary battery according to claim 6, characterized in that: The extension portion (202) extends along the thickness direction of the composite current collector (10) in a direction away from the composite current collector (10) and is attached to the active material layer (30).

10. The secondary battery according to claim 6, characterized in that: The length of the extension track from one end of the extension portion (202) away from the main body portion (201) to one end connected to the main body portion (201) is 1 mm to 10 mm.

11. An electrical device, characterized in that: The secondary battery comprises the secondary battery according to any one of claims 1 to 10, wherein the secondary battery is used as a power supply for the electrical device.

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