Rechargeable battery and electronic device

Abstract

The present application relates to a rechargeable battery and an electronic device. The rechargeable battery comprises a first electrode sheet and a second electrode sheet, which have opposite polarities, wherein the first electrode sheet comprises a first current collector and a first active layer; the first current collector comprises a first metal layer, a first polymer layer and a second metal layer; in the direction of thickness of the first current collector, the first metal layer and the second metal layer are respectively provided on two opposite surfaces of the first polymer layer; the first active layer is provided on the surface of the first metal layer that faces away from the first polymer layer; the first metal layer is electrically connected to first tabs; the first electrode sheet is a cathode electrode sheet; there are N first tabs; and in the direction of thickness of the first current collector, the thickness of the first metal layer and the thickness of the second metal layer are H1, where 1 / N μm≤H1≤5 μm. The rechargeable battery and electronic device of the present application can improve the balance between the charge-discharge rate performance and safety performance of the rechargeable battery.

Description

Secondary batteries and electronic devices

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 202411745835.X, filed on November 29, 2024, entitled "Secondary Battery and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a secondary battery and electronic device. Background Technology

[0004] Secondary batteries, as the power source for electronic devices, are crucial for ensuring their normal operation. To improve energy density and safety, secondary batteries often feature a composite current collector (a three-layer sandwich structure of metal layer-polymer layer-metal layer). To achieve good charge / discharge rate performance, the metal layer of the composite current collector needs to be thickened; however, a thicker metal layer results in poorer safety performance for the secondary battery. Summary of the Invention

[0005] The purpose of this application is to provide a secondary battery and electronic device that aims to improve the balance between the charge / discharge rate performance and safety performance of the secondary battery.

[0006] According to a first aspect of this application, a secondary battery is provided, comprising a first electrode and a second electrode with opposite polarities. The first electrode includes a first current collector and a first active layer. The first current collector includes a first metal layer, a first polymer layer, and a second metal layer. Along the thickness direction of the first current collector, the first metal layer and the second metal layer are respectively disposed on opposite surfaces of the first polymer layer. The first active layer is disposed on the surface of the first metal layer facing away from the first polymer layer. The first metal layer is electrically connected to a first tab. The first electrode is a positive electrode, and the number of first tabs is N. Along the thickness direction of the first current collector, the thickness of both the first metal layer and the thickness of the second metal layer are H1, where 1 / Nμm≤H1≤5μm.

[0007] In the above technical solution, the first current collector includes a first metal layer, a first polymer layer, and a second metal layer. The thickness of the first and second metal layers can be reduced to improve the energy density and safety performance of the secondary battery. The first metal layer is electrically connected to a first tab, which is used to transmit the current from the first electrode to an external electronic device. The number of first tabs is N, and the thickness of the first and second metal layers is H1. In practical applications, the optimal thickness of the first and second metal layers during mass production of the first current collector is 1 μm, and the first and second metal layers of this thickness have good conductivity. By limiting H1 ≥ 1 / N μm, the secondary battery can have good charge / discharge rate performance with different numbers of first tabs. Since increasing the thickness of the first and second metal layers will increase the metal burrs caused by mechanical damage to the secondary battery, thereby affecting the safety performance of the secondary battery, by limiting H1 ≤ 5 μm, the secondary battery can have good safety performance. In summary, by limiting 1 / N μm ≤ H1 ≤ 5 μm, the secondary battery can have both good charge / discharge rate performance and safety performance with different numbers of first tabs. It should be noted that the thickness of both the first metal layer and the second metal layer is H1, but due to process variations, the thicknesses of the first metal layer and the second metal layer may not be equal.

[0008] In some preferred embodiments, 1.5 / Nμm≤H1≤5μm is used to further improve the charge / discharge rate performance of the secondary battery.

[0009] In some preferred embodiments, N=1, and 1.5μm≤H1≤3μm. When the number of first tabs is single, the current transmission effect of a single first tab is poor. To improve the charge / discharge rate performance, it is necessary to increase the thickness of the first metal layer and the second metal layer. By limiting H1≥1.5μm, the charge / discharge rate performance of the secondary battery is improved; by limiting H1≤3μm, the safety performance of the secondary battery is improved.

[0010] In some preferred embodiments, the thickness of the first polymer layer is H2, where 2μm ≤ H2 ≤ 12μm. The first polymer layer of the first current collector serves as a support layer, providing mechanical properties. If the thickness H1 of the first metal layer and the second metal layer is ≥ 1.5μm, the first and second metal layers can also provide mechanical properties; therefore, the thickness of the first polymer layer can be ≤ 12μm. Furthermore, increasing the thickness of the first polymer layer will reduce the energy density of the secondary battery. By limiting the thickness to 2μm ≤ H2 ≤ 12μm, the first polymer layer can possess good mechanical properties while the secondary battery maintains a good energy density.

[0011] In some preferred embodiments, the first active layer has a first groove, and the first tab is disposed in the first groove to improve the volumetric energy density of the secondary battery.

[0012] In some preferred embodiments, N=2, and 1μm≤H1≤3μm. When there are two first tabs, the current transfer effect of two first tabs is better than that of a single first tab, and the thickness of the first metal layer and the second metal layer can be reduced. By limiting H1≥1μm, the charge / discharge rate performance of the secondary battery is improved, and by limiting H1≤3μm, the safety performance of the secondary battery is improved.

[0013] In some preferred embodiments, 1 μm ≤ H1 ≤ 1.5 μm, and the thickness of the first polymer layer is H2, where 2.9 μm ≤ H2 ≤ 12 μm. If the thickness H1 of the first and second metal layers is between 1 μm and 1.5 μm, the first and second metal layers can also provide mechanical properties, thus the first polymer layer can be thinned. Furthermore, increasing the thickness of the first polymer layer would reduce the energy density of the secondary battery. By limiting the thickness to 2.9 μm ≤ H2 ≤ 12 μm, the first polymer layer can have good mechanical properties while the secondary battery has good energy density.

[0014] In some preferred embodiments, the first active layer has a first groove and a second groove, which are spaced apart, and two first tabs are respectively disposed in the first groove and the second groove to improve the volumetric energy density of the secondary battery.

[0015] In some preferred embodiments, N ≥ 3, and 0.5 μm ≤ H1 ≤ 3 μm. When the number of first tabs is three or more, three first tabs provide better current transfer than two first tabs, and the thickness of the first metal layer and the second metal layer can be reduced. By limiting H1 ≥ 0.5 μm, the charge / discharge rate performance of the secondary battery is improved; by limiting H1 ≤ 3 μm, the safety performance of the secondary battery is improved.

[0016] In some preferred embodiments, 0.5 μm ≤ H1 ≤ 1 μm, and the thickness of the first polymer layer is H2, where 4.5 μm ≤ H2 ≤ 12 μm. If the thickness H1 of the first and second metal layers is between 0.5 μm and 1 μm, the thickness of the first polymer layer needs to be increased to improve mechanical properties. Furthermore, increasing the thickness of the first polymer layer will reduce the energy density of the secondary battery. By limiting the thickness to 4.5 μm ≤ H2 ≤ 12 μm, the first polymer layer can have good mechanical properties while the secondary battery has good energy density.

[0017] In some preferred embodiments, the number of first electrodes is the same as the number of first tabs, and a first metal layer of a first electrode is connected to a first tab. Increasing the number of first electrodes can reduce the length and width of any one first electrode, thereby improving the charge / discharge rate performance of any one first electrode.

[0018] In some preferred embodiments, the first electrode includes a second active layer, and the second active layer is disposed on the surface of the second metal layer away from the surface of the first polymer layer, which can reduce the number of layers of the first electrode in the secondary battery, thereby increasing the energy density.

[0019] In some preferred embodiments, the surface of the first metal layer facing away from the first polymer layer includes a first region and a second region connected together. The first region is provided with a first active layer, while the second region is not provided with a first active layer and is provided with a first tab. The surface of the second metal layer facing away from the first polymer layer includes a third region and a fourth region connected together. The third region is provided with a second active layer, while the fourth region is not provided with a second active layer. Along the thickness direction of the first current collector, the projection of the fourth region onto the first metal layer at least partially overlaps with the second region. When the first tab is disposed in the second region, the fourth region can provide accommodating space to improve the convenience of disposing of the first tab in the second region.

[0020] In some preferred embodiments, the first metal layer comprises at least one of aluminum, copper, nickel, titanium, silver, and zirconium. And / or, the second metal layer comprises at least one of aluminum, copper, nickel, titanium, silver, and zirconium.

[0021] In some preferred embodiments, the first polymer layer includes at least one of polyethylene, polypropylene, polyimide, polytetrafluoroethylene, and polyester.

[0022] In some preferred embodiments, the first tab, the first metal layer, and the second metal layer are connected by riveting or roll welding to make the first tab, the first metal layer, and the second metal layer electrically conductive.

[0023] In some preferred embodiments, the first metal layer and the second metal layer are both electroplated onto opposite surfaces of the first polymer layer. Alternatively, the first metal layer and the second metal layer are both vapor-deposited onto opposite surfaces of the first polymer layer.

[0024] Secondly, this application also proposes an electronic device including a secondary battery as described in any of the embodiments of the first aspect above.

[0025] The inventors of this application have discovered that designing the positive electrode current collector of a secondary battery as a composite current collector (a three-layer sandwich structure of metal layer-polymer layer-metal layer) can improve energy density and safety performance. To achieve good charge / discharge rate performance, the metal layer of the composite current collector needs to be thicker; however, a thicker metal layer results in poorer safety performance of the secondary battery. The charge / discharge rate performance of the secondary battery varies with the number of tabs, therefore the required thickness of the metal layer of the composite current collector also varies. This application defines an optimal range for the thickness of the metal layer of the first current collector for different numbers of first tabs, in order to improve the balance between charge / discharge rate performance and safety performance of the secondary battery.

[0026] Additional aspects and advantages of the embodiments of this application will be described, shown, or illustrated in part by way of implementation of the embodiments of this application in the following description. Attached Figure Description

[0027] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Elements having the same reference numerals in the drawings are denoted as similar elements. Unless otherwise stated, the dimensions in the drawings do not constitute a limitation on scale.

[0028] Figure 1 is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0029] Figure 2 is a schematic diagram of the structure of an electrode assembly according to some embodiments of this application;

[0030] Figure 3 is a partial schematic diagram of an electrode assembly according to some embodiments of this application;

[0031] Figure 4 is a schematic diagram of the structure of the first electrode plate and the first electrode tab in some embodiments of this application;

[0032] Figure 5 is a schematic diagram of the structure of the first electrode and the first electrode tab in some embodiments of this application.

[0033] Explanation of reference numerals in the attached figures:

[0034] 100. Secondary batteries;

[0035] 10. Shell;

[0036] 20. Electrode assembly;

[0037] 21. First electrode; 211. First current collector; 2111. First polymer layer; 2112. First metal layer; 211a. First region; 211b. Second region; 2113. Second metal layer; 211c. Third region; 211d. Fourth region; 212. First active layer; 2121. First groove; 2122. Second groove; 213. Second active layer;

[0038] 22. Second electrode; 221. Second current collector; 222. Third active layer; 223. Fourth active layer;

[0039] 23. Diaphragm; 24. First tab; 25. Second tab; 26. Connector;

[0040] X, the first direction. Embodiments of the present invention

[0041] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this application, but not all embodiments.

[0042] In this application, the reference to "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0043] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0044] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0045] The technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0046] In a first aspect, embodiments of this application provide a secondary battery 100. Referring to FIG1, the secondary battery 100 includes a housing 10 and an electrode assembly 20. The housing 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure), and the electrolyte wets the electrode assembly 20 within the housing 10.

[0047] Referring to Figure 2, which illustrates the wound structure of the electrode assembly 20, the electrode assembly 20 includes a first electrode 21, a diaphragm 23, and a second electrode 22. The first electrode 21 and the second electrode 22 have opposite polarities. A diaphragm 23 is disposed between adjacent second electrode 22 and first electrode 21. The first electrode 21, diaphragm 23, and second electrode 22 are stacked and wound together. Exemplarily, along the thickness direction of the first electrode 21 and / or the second electrode 22, the first electrode 21, diaphragm 23, and second electrode 22 are sequentially stacked and then wound to form a wound electrode assembly 20. In the embodiments of this application, a wound structure is used as an example for illustration. In other embodiments, the electrode assembly 20 may also be a stacked structure. For example, along the thickness direction of the first electrode 21 and / or the second electrode 22, the first electrode 21, diaphragm 23, and second electrode 22 are sequentially stacked to form a stacked electrode assembly 20.

[0048] Regarding the first electrode 21 mentioned above, please refer to Figure 3. The first electrode 21 includes a first current collector 211 and a first active layer 212. The first active layer 212 is disposed on one surface of the first current collector 211.

[0049] The first current collector 211 includes a first metal layer 2112, a first polymer layer 2111, and a second metal layer 2113. Along the thickness direction (first direction X) of the first current collector 211, the first metal layer 2112 and the second metal layer 2113 are respectively disposed on opposite surfaces of the first polymer layer 2111. A first active layer 212 is disposed on the surface of the first metal layer 2112 facing away from the first polymer layer 2111. The first polymer layer 2111, serving as the main mechanical support layer of the first current collector 211, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), polyimide, polytetrafluoroethylene, and polyester. The first metal layer 2112 may include at least one of aluminum, copper, nickel, titanium, silver, and zirconium. The second metal layer 2113 may include at least one of aluminum, copper, nickel, titanium, silver, and zirconium. By using the first polymer layer 2111 as the main mechanical support layer, the metal layers of the first current collector 211 can be thinned, thereby reducing metal burrs caused by mechanical damage to the secondary battery 100 and reducing the mass of the first current collector 211, thus increasing the mass energy density of the secondary battery 100. In some other embodiments, the first current collector 211 may be a single-layer metal foil, which may include at least one of aluminum, copper, nickel, titanium, and silver.

[0050] In some embodiments, the first metal layer 2112 and the second metal layer 2113 are both electroplated onto the opposite surfaces of the first polymer layer 2111. Alternatively, the first metal layer 2112 and the second metal layer 2113 are both vapor-deposited onto the opposite surfaces of the first polymer layer 2111.

[0051] The first active layer 212 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The first active layer 212 comprises a first active material, a conductive agent, an adhesive, etc. These materials are mixed and stirred evenly and then coated onto the surface of the first metal layer 2112 facing away from the first polymer layer 2111, thereby obtaining the first active layer 212. The first active material may include at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium manganese oxide, and lithium manganese iron phosphate.

[0052] In some embodiments, the first electrode 21 includes a second active layer 213. The second metal layer 2113 is disposed on the surface opposite to the first polymer layer 2111, which can reduce the number of layers of the first electrode 21 in the secondary battery 100, thereby increasing the energy density.

[0053] In some embodiments, the first current collector 211 is provided with a first tab 24. The first tab 24, the first metal layer 2112, and the second metal layer 2113 are connected by riveting or roll welding to enable electrical conductivity between the first tab 24, the first metal layer 2112, and the second metal layer 2113. In some embodiments, the number of first tabs 24 is one or two. The first tab 24, the first metal layer 2112, and the second metal layer 2113 are riveted together by a connector 26. For example, the connector 26 passes through the first metal layer 2112, the first polymer layer 2111, and the second metal layer 2113 and is connected to the first tab 24. The connector 26 can be a rivet.

[0054] In some embodiments, the number of first tabs 24 is greater than two, and the first tabs 24, the first metal layer 2112 and the second metal layer 2113 are connected by roll welding.

[0055] In some embodiments, the surface of the first metal layer 2112 away from the surface of the first polymer layer 2111 includes a first region 211a and a second region 211b connected together. The first region 211a is provided with a first active layer 212, and the second region 211b is not provided with a first active layer 212. The second region 211b is provided with a first tab 24, which is used to transmit the current of the first electrode 21 to an external electronic device. The second metal layer 2113 away from the surface of the first polymer layer 2111 includes a third region 211c and a fourth region 211d connected together. The third region 211c is provided with a second active layer 213, and the fourth region 211d is not provided with a second active layer 213. Along the thickness direction of the first current collector 211, the projection of the fourth region 211d onto the first metal layer 2112 overlaps at least partially with the second region 211b. Since the first electrode 24 needs to be set on the first current collector 211 via a connecting device (e.g., a welding device), when the first electrode 24 is set in the second region 211b, a portion of the connecting device can simultaneously extend into the second region 211b and the fourth region 211d to improve the convenience of the connecting device in setting the first electrode 24 in the second region 211b.

[0056] The second electrode 22 mentioned above includes a second current collector 221 and a third active layer 222. The surface of the second current collector 221 facing the first active layer 212 is provided with a second active layer 213.

[0057] In some embodiments, a fourth active layer 223 is provided on the surface of the second current collector 221 facing away from the first active layer 212, so as to reduce the number of layers of the second electrode 22 in the secondary battery 100, thereby increasing the energy density of the secondary battery 100.

[0058] In some embodiments, please refer to FIG2, the second electrode 22 is provided with a second tab 25, which is used to transmit the current of the second electrode 22 to an external electronic device.

[0059] The second current collector 221 can be a metal foil, such as a copper foil. The second current collector 221 can also be a composite current collector (a composite structure of metal-polymer-metal). For example, the second current collector 221 includes a polymer layer and metal layers disposed on opposite surfaces of the polymer layer. The polymer layer, as the main mechanical support layer of the second current collector 221, can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE). The metal layer can include at least one of aluminum, copper, nickel, titanium, and silver. By using the polymer layer as the main mechanical support layer, the metal layer of the second current collector 221 can be thinned, thereby reducing metal burrs caused by mechanical damage to the secondary battery 100 and reducing the mass of the second current collector 221, thus increasing the mass energy density of the secondary battery 100. In some other embodiments, the second current collector 221 can be a single-layer metal foil, which can include at least one of aluminum, copper, nickel, titanium, and silver.

[0060] The third active layer 222 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The third active layer 222 comprises a third active material, a conductive agent, an adhesive, etc. These materials are mixed and stirred evenly and then coated onto the surface of the second current collector 221 facing the first active layer 212, thereby obtaining the third active layer 222. The third active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0061] The fourth active layer 223 is immersed in the electrolyte within the housing 10 to undergo an electrochemical reaction. The fourth active layer 223 comprises a fourth active material, a conductive agent, an adhesive, etc. These materials are mixed and stirred evenly and then coated onto the surface of the second current collector 221 facing away from the first active layer 212, thereby obtaining the fourth active layer 223. The fourth active material may include at least one of graphite, silicon, hard carbon, and carbon fiber.

[0062] In some embodiments, referring to Figures 2 and 3, the first electrode 21 is a positive electrode, and the first metal layer 2112 of the first current collector 211 is electrically connected to the first tab 24, which is used to transmit the current from the first electrode 21 to an external electronic device. To achieve good charge / discharge rate performance, the metal layer of the first current collector 211 needs to be thickened in the secondary battery 100; however, a thicker metal layer results in poorer safety performance for the secondary battery 100. The charge / discharge rate performance of the secondary battery 100 varies with the number of tabs, therefore the required thickness of the metal layer of the first current collector 211 also varies.

[0063] To address the aforementioned issues, in the embodiments of this application, the number of first tabs 24 is N, and the thicknesses of the first metal layer 2112 and the second metal layer 2113 along the thickness direction of the first current collector 211 are H1, where 1 / Nμm ≤ H1 ≤ 5μm. In practical applications, the optimal thickness of the first metal layer 2112 and the second metal layer 2113 during mass production of the first current collector 211 is 1μm, and this thickness of the first metal layer 2112 and the second metal layer 2113 exhibits good conductivity. By limiting H1 ≥ 1 / Nμm, the secondary battery 100 can achieve good charge / discharge rate performance regardless of the number of first tabs 24. Since increasing the thickness of the first metal layer 2112 and the second metal layer 2113 increases the likelihood of metal burrs in the secondary battery 100 during mechanical damage, thereby affecting the safety performance of the secondary battery 100, limiting H1 ≤ 5μm ensures good safety performance of the secondary battery 100. In summary, by limiting 1 / Nμm ≤ H1 ≤ 5μm, the secondary battery 100 can simultaneously possess good charge / discharge rate performance and safety performance regardless of the number of first tabs 24. It should be noted that the thickness of both the first metal layer 2112 and the second metal layer 2113 is H1, but due to process variations, the thicknesses of the first metal layer 2112 and the second metal layer 2113 may not be equal.

[0064] In some embodiments, 1.5 / Nμm≤H1≤5μm, to further improve the charge / discharge rate performance of the secondary battery 100.

[0065] In some embodiments, N=1, and 1.5μm≤H1≤3μm. When the number of first tabs 24 is single, the current transmission effect of a single first tab 24 is poor. To improve the charge / discharge rate performance, it is necessary to increase the thickness of the first metal layer 2112 and the second metal layer 2113. By limiting H1≥1.5μm, the charge / discharge rate performance of the secondary battery 100 is improved; by limiting H1≤3μm, the safety performance of the secondary battery 100 is improved.

[0066] In some embodiments, the thickness of the first polymer layer 2111 is H2, where 2μm ≤ H2 ≤ 12μm. The first polymer layer 2111 of the first current collector 211 serves as a support layer, providing mechanical properties. If the thickness H1 of the first metal layer 2112 and the second metal layer 2113 is ≥ 1.5μm, the first metal layer 2112 and the second metal layer 2113 can also provide mechanical properties. Therefore, the thickness of the first polymer layer 2111 can be ≤ 12μm. Furthermore, increasing the thickness of the first polymer layer 2111 will reduce the energy density of the secondary battery 100. By limiting 2μm ≤ H2 ≤ 12μm, the first polymer layer 2111 can have good mechanical properties while the secondary battery 100 has good energy density.

[0067] In some embodiments, please refer to FIG4, the first active layer 212 has a first groove 2121, and the first tab 24 is disposed in the first groove 2121 to improve the volumetric energy density of the secondary battery 100.

[0068] In some embodiments, N=2, 1μm≤H1≤3μm. When there are two first tabs 24, the current transmission effect of two first tabs 24 is better than that of a single first tab 24, and the thickness of the first metal layer 2112 and the second metal layer 2113 can be reduced. By limiting H1≥1μm, the charge / discharge rate performance of the secondary battery 100 is improved, and by limiting H1≤3μm, the safety performance of the secondary battery 100 is improved.

[0069] In some embodiments, 1 μm ≤ H1 ≤ 1.5 μm, and the thickness of the first polymer layer 2111 is H2, where 2.9 μm ≤ H2 ≤ 12 μm. If the thickness H1 of the first metal layer 2112 and the second metal layer 2113 is 1 μm to 1.5 μm, the first polymer layer 2112 plays two roles in the composite current collector. First, it provides a carrier for the first metal layer 2112 and the second metal layer 2113. Since the first metal layer 2112 and the second metal layer 2113 are deposited onto the first polymer layer 2111 by vapor deposition in the composite current collector, if the first polymer layer 2111 is too thin, it is difficult to form a thicker first metal layer 2112 and the second metal layer 2113 on its surface. Therefore, according to the first metal layer 2111... The thickness of the first polymer layer 2111 is determined by the thickness of the first metal layer 2112 and the second metal layer 2113. On the one hand, the first polymer layer 2111 provides mechanical support for the entire first current collector 211; on the other hand, the first polymer layer 2111 provides mechanical support for the first current collector 2111. Therefore, when the first metal layer 2112 and the second metal layer 2113 are relatively thick, they can also contribute to improving mechanical properties. Thus, the first polymer layer 2111 can be made less than 12 μm. Furthermore, increasing the thickness of the first polymer layer 2111 will reduce the energy density of the secondary battery 100. By limiting the thickness to 2.9 μm ≤ H2 ≤ 12 μm, the first polymer layer 2111 does not affect the arrangement of the first metal layer 2112 and the second metal layer 2113, and while possessing good mechanical properties, the secondary battery 100 also has a good energy density.

[0070] In some embodiments, please refer to FIG5, the first active layer 212 has a first groove 2121 and a second groove 2122, the first groove 2121 and the second groove 2122 are spaced apart, and two first tabs 24 are respectively disposed in the first groove 2121 and the second groove 2122 to improve the volumetric energy density of the secondary battery 100.

[0071] In some embodiments, N≥3, 0.5μm≤H1≤3μm. When the number of first tabs 24 is three or more, three first tabs 24 are better at transmitting current than two first tabs 24, and the thickness of the first metal layer 2112 and the second metal layer 2113 can be reduced. By limiting H1≥0.5μm, the charge / discharge rate performance of the secondary battery 100 is improved; by limiting H1≤3μm, the safety performance of the secondary battery 100 is improved.

[0072] In some embodiments, 0.5 μm ≤ H1 ≤ 1 μm, the thickness of the first polymer layer 2111 is H2, and 4.5 μm ≤ H2 ≤ 12 μm. If the thickness H1 of the first metal layer 2112 and the second metal layer 2113 is 0.5 μm to 1 μm, the thickness of the first polymer layer 2111 needs to be increased to improve mechanical properties. Furthermore, increasing the thickness of the first polymer layer 2111 will reduce the energy density of the secondary battery 100. By limiting the thickness to 4.5 μm ≤ H2 ≤ 12 μm, the first polymer layer 2111 can have good mechanical properties while the secondary battery 100 has good energy density.

[0073] In some embodiments, the number of first electrode plates 21 is the same as the number of first tabs 24, and a first metal layer 2112 of a first electrode plate 21 is connected to a first tab 24. Increasing the number of first electrode plates 21 can reduce the length and width of any first electrode plate 21, thereby improving the charge and discharge rate performance of any first electrode plate 21.

[0074] A second aspect of this application also proposes an electronic device including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device in this application is not particularly limited and can be any electronic device known in the prior art. For example, electronic devices include, but are not limited to, Bluetooth headsets, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0075] Test section:

[0076] 1. Rate performance testing of lithium-ion batteries:

[0077] Test procedure: The test was conducted at 23±2℃. The battery cell was discharged to 3V at a rate of 0.2C, and then charged to 4.5V at a rate of 0.2C. The discharge and charge process was repeated. The discharge rates were 0.2C, 0.7C, 1.5C, 3C, and 6C to discharge to 3V, and the charge rate was 0.2C to charge to 4.5V. The discharge capacity at 0.2C after full charge to 4.5V was used as the benchmark. The discharge capacity at subsequent rates of 0.7C, 1.5C, 3C, and 6C was divided by the benchmark value to obtain the rate performance evaluation value.

[0078] 2. Impact test of lithium-ion batteries:

[0079] Test procedure: In a test environment of 20±5℃, place the sample on the test platform with the inkjet side facing up. Place a 15.8mm diameter round bar at the center of the wide side of the sample, with the round bar perpendicular to the long axis of the sample. Use a 9.1±0.1kg weight to drop it vertically from a height of 610±25mm in a free state, and drop it at the intersection of the round bar and the sample. Judgment criteria: No fire or explosion.

[0080] Impact test pass rate = number of cells that pass / total number of cells tested.

[0081] Example 1

[0082] <Preparation of the positive electrode>:

[0083] Lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 97.5:1.0:1.5. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry with a solid content of 75 wt%, and the mixture was stirred evenly.

[0084] Polyethylene terephthalate (PET) was selected as the polymer layer, with a thickness of 6 μm. Two 1 μm thick aluminum metal layers were deposited on the two surfaces of the polymer layer to obtain the positive electrode current collector. The above slurry was coated on the surface of one metal layer of the positive electrode current collector, leaving a blank positive electrode foil section. The slurry was dried to obtain a single-sided positive electrode sheet with a positive active material layer coated on one side. The above steps were repeated on the other metal layer to obtain a double-sided positive electrode sheet with a positive active material layer coated on both sides. The double-sided positive electrode sheet was provided with a single positive electrode tab.

[0085] <Preparation of negative electrode sheet>:

[0086] Using graphite as the negative electrode active material, graphite, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener are mixed in a weight ratio of 96:2:2. Deionized water is added as a solvent to prepare a slurry with a solid content of 70wt%, and the mixture is stirred evenly.

[0087] Copper foil was selected as the negative electrode current collector. The above-mentioned slurry was coated on the surface of the negative electrode current collector, leaving a blank section for the negative electrode foil. The slurry was dried to obtain a single-sided negative electrode sheet with a negative electrode active material layer coated on one side. The above steps were repeated on the other surface of the negative electrode current collector to obtain a double-sided negative electrode sheet with a negative electrode active material layer coated on both sides.

[0088] <Preparation of the diaphragm>:

[0089] A porous polyethylene membrane is used as the substrate layer, and a ceramic layer containing alumina ceramic and PVDF binder is coated on one side of the substrate layer as a separator (CCS). The mass percentage of alumina ceramic in the ceramic layer is 95%.

[0090] <Electrolyte Preparation>:

[0091] In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are first mixed in a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent. Then, lithium salt lithium hexafluorophosphate (LiPF6) is added to the basic organic solvent, dissolved, and mixed evenly to obtain an electrolyte with a LiPF6 mass concentration of 12.5%.

[0092] <Preparation of Lithium-ion Batteries>:

[0093] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound to form the electrode assembly. This assembly is placed in an aluminum-plastic film packaging bag, dried, and then injected with electrolyte. Following vacuum sealing, settling, formation, capacity testing, degassing, and edge trimming, a lithium-ion battery is obtained.

[0094] The relevant parameters in Comparative Examples 1 to 5 and Examples 1 to 26 are shown in Table 1 below.

[0095] The number of positive electrode tabs in Comparative Examples 1 to 3 and Examples 1 to 9 is a single one. Among them, the only difference between Comparative Examples 2 to 3 and Examples 1 to 5 is the thickness of the metal layer of the positive electrode current collector. The thickness of both the metal layer and the polymer layer of the positive electrode current collector in Comparative Examples 1 and Example 9 are adjusted. The only difference between Examples 6 to 8 is the thickness of the polymer layer of the positive electrode current collector.

[0096] The number of positive electrode tabs in Comparative Example 4 and Examples 10 to 18 are all two. Among them, the only difference between Comparative Example 4 and Examples 10 to 16 is the thickness of the metal layer of the positive electrode current collector, while the only difference between Examples 17 and 18 is the thickness of the polymer layer of the positive electrode current collector.

[0097] The number of positive electrode tabs in Comparative Example 5 and Examples 19 to 26 are all three or more. Among them, Comparative Example 5 and Examples 19 to 24 differ only in the thickness of the metal layer of the positive electrode current collector, while Examples 25 to 26 differ only in the thickness of the polymer layer of the positive electrode current collector.

[0098] Table 1

[0099]

[0100]

[0101]

[0102] Note: In Table 1, "\" indicates that the parameter is not included, and "*" indicates that the parameter is close to 100%.

[0103] According to Table 1 above, and in conjunction with Comparative Examples 1 to 5, Examples 1 to 5, and Examples 8 to 9, when the number of positive electrode tabs is N, if the thickness H1 of the metal layer of the positive electrode composite current collector is < 1 / N μm (where 1 μm is the optimal thickness for mass production of the metal layer of the positive electrode composite current collector, and a metal layer of this thickness has good conductivity), the secondary battery has good safety performance, but poor rate performance. If H1 > 5 μm, the secondary battery has good rate performance, but poor safety performance. If 1 / N μm ≤ H1 ≤ 5 μm, compared with Comparative Examples 1 to 5, the secondary battery can simultaneously possess good rate performance and safety performance.

[0104] Based on Examples 1 to 2, Examples 10 to 11, and Examples 19 to 20, it can be seen that when the number of positive electrode tabs is N, if the thickness H1 of the metal layer of the positive electrode composite current collector is ≥1.5 / Nμm, the secondary battery can have better rate performance.

[0105] As can be seen from Examples 1 to 5, when the number of positive electrode tabs is single and the polymer layer thickness of the positive electrode composite current collector is 6 μm, if the thickness H1 of the metal layer of the positive electrode composite current collector is <1.5 μm, the rate performance of the secondary battery at a discharge rate of 0.2C is less than 90%. If H1 > 3 μm, the impact test pass rate of the secondary battery is less than 80%. Therefore, when the number of positive electrode tabs is single, the thickness H1 of the metal layer of the positive electrode composite current collector is preferably 1.5 μm to 3 μm.

[0106] As can be seen from Examples 10 to 16, when there are two positive electrode tabs and the polymer layer thickness of the positive electrode composite current collector is 6 μm, if the metal layer thickness H1 of the positive electrode composite current collector is less than 1 μm, the rate performance of the secondary battery at a discharge rate of 0.2C is less than 90%. If H1 > 3 μm, the impact test pass rate of the secondary battery is less than 80%. Therefore, when there are two positive electrode tabs, the metal layer thickness H1 of the positive electrode composite current collector is preferably 1 μm to 3 μm.

[0107] As can be seen from Examples 19 to 24, when the number of positive electrode tabs N≥3 and the polymer layer thickness of the positive electrode composite current collector is 6μm, if the metal layer thickness H1 of the positive electrode composite current collector is >0.5μm, the rate performance of the secondary battery at a 6C discharge rate is not less than 90%. If H1>3μm, the impact test pass rate of the secondary battery is less than 80%. Therefore, when the number of positive electrode tabs N≥3, the metal layer thickness H1 of the positive electrode composite current collector is preferably 0.5μm to 3μm.

[0108] Based on Examples 20, 25, and 26, it can be seen that when the thickness H1 of the metal layer of the positive electrode composite current collector is 1 μm, if the thickness H2 of the polymer layer of the positive electrode composite current collector is 4.5 μm to 12 μm, it has little impact on the rate performance and safety performance of the secondary battery. In practical applications, the polymer layer of the positive electrode composite current collector acts as a support layer, providing mechanical properties. If the thickness H1 of the metal layer of the positive electrode composite current collector is ≤ 1 μm, the thickness H2 of the polymer layer of the positive electrode composite current collector needs to be no less than 4.5 μm to provide better mechanical properties. However, if the thickness H2 of the polymer layer of the positive electrode composite current collector exceeds 12 μm, it will reduce the energy density of the secondary battery. Therefore, when the thickness H1 of the metal layer of the positive electrode composite current collector is ≤ 1 μm, the thickness H2 of the polymer layer of the positive electrode composite current collector is preferably 4.5 μm to 12 μm.

[0109] Based on Examples 13, 17, and 18, it can be seen that when the thickness H1 of the metal layer of the positive electrode composite current collector is 1.5 μm, if the thickness H2 of the polymer layer of the positive electrode composite current collector is 2.9 μm to 12 μm, it has little impact on the rate performance and safety performance of the secondary battery. In practical applications, the polymer layer of the positive electrode composite current collector acts as a support layer, providing mechanical properties. If the thickness of the metal layer of the positive electrode composite current collector is 1 μm ≤ H1 ≤ 1.5 μm, the metal layer can also provide mechanical properties. The polymer layer can be thinned, and the lower limit of the polymer layer thickness H2 can be reduced from 4.5 μm to 2.9 μm. However, if the thickness H2 of the polymer layer of the positive electrode composite current collector exceeds 12 μm, it will reduce the energy density of the secondary battery. Therefore, when the thickness H1 of the metal layer of the positive electrode composite current collector is 1 μm to 1.5 μm, the thickness H2 of the polymer layer of the positive electrode composite current collector is preferably 2.9 μm to 12 μm.

[0110] Based on Examples 4 and 6 to 8, when the thickness H1 of the metal layer of the positive electrode composite current collector is 3 μm, if the thickness H2 of the polymer layer of the positive electrode composite current collector is 2 μm to 12 μm, it has little impact on the rate performance of the secondary battery. In practical applications, the polymer layer of the positive electrode composite current collector acts as a support layer, providing mechanical properties. If the thickness H1 of the metal layer of the positive electrode composite current collector is ≥ 1.5 μm, the metal layer can also provide mechanical properties. The polymer layer can be thinned, and the lower limit of the polymer layer thickness H2 can be reduced from 2.9 μm to 2 μm. If H2 is lower than 2 μm, the impact test pass rate of the secondary battery will be less than 60%. If H2 exceeds 12 μm, it will reduce the energy density of the secondary battery. Therefore, when the thickness H1 of the metal layer of the positive electrode composite current collector is ≥ 1.5 μm, the thickness H2 of the polymer layer of the positive electrode composite current collector is preferably 2 μm to 12 μm.

[0111] The above description is merely an embodiment of this application and does not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A secondary battery, comprising a first electrode and a second electrode with opposite polarities, the first electrode comprising a first current collector and a first active layer, the first current collector comprising a first metal layer, a first polymer layer and a second metal layer, wherein the first metal layer and the second metal layer are respectively disposed on opposite surfaces of the first polymer layer along the thickness direction of the first current collector; the first active layer is disposed on the surface of the first metal layer opposite to the first polymer layer, and the first metal layer is electrically connected to a first tab; Its features are, The first electrode is a positive electrode, and the number of the first tabs is N. Along the thickness direction of the first current collector, the thickness of the first metal layer and the thickness of the second metal layer are both H1, and 1 / Nμm≤H1≤5μm.

2. The secondary battery according to claim 1, characterized in that, 1.5 / Nμm≤H1≤5μm.

3. The secondary battery according to claim 2, characterized in that, N=1, 1.5μm≤H1≤3μm.

4. The secondary battery according to claim 3, characterized in that, The thickness of the first polymer layer is H2, where 2μm≤H2≤12μm.

5. The secondary battery according to claim 3 or 4, characterized in that, The first active layer has a first groove, and the first electrode tab is disposed in the first groove.

6. The secondary battery according to claim 2, characterized in that, N=2, 1μm≤H1≤3μm.

7. The secondary battery according to claim 6, characterized in that, 1μm≤H1≤1.5μm, the thickness of the first polymer layer is H2, 2.9μm≤H2≤12μm.

8. The secondary battery according to claim 6 or 7, characterized in that, The first active layer has a first groove and a second groove, which are spaced apart, and the two first tabs are respectively disposed in the first groove and the second groove.

9. The secondary battery according to claim 2, characterized in that, N≥3, 0.5μm≤H1≤3μm.

10. The secondary battery according to claim 9, characterized in that, 0.5μm≤H1≤1μm, the thickness of the first polymer layer is H2, 4.5μm≤H2≤12μm.

11. The secondary battery according to claim 9 or 10, characterized in that, The number of first electrode plates is the same as the number of first electrode tabs, and a first metal layer of each first electrode plate is connected to a first electrode tab.

12. The secondary battery according to any one of claims 1 to 11, characterized in that, The first electrode includes a second active layer, and the second active layer is disposed on the surface of the second metal layer opposite to the surface of the first polymer layer.

13. The secondary battery according to claim 12, characterized in that, The surface of the first metal layer away from the first polymer layer includes a first region and a second region connected together. The first region is provided with the first active layer, the second region is not provided with the first active layer, and the second region is provided with the first tab. The surface of the second metal layer away from the first polymer layer includes a connected third region and a fourth region. The third region is provided with the second active layer, and the fourth region is not provided with the second active layer. Along the thickness direction of the first current collector, the projection of the fourth region onto the first metal layer at least partially overlaps with the second region.

14. The secondary battery according to any one of claims 1-13, characterized in that, The first metal layer comprises at least one of aluminum, copper, nickel, titanium, silver, and zirconium; and / or the second metal layer comprises at least one of aluminum, copper, nickel, titanium, silver, and zirconium; and / or the first polymer layer comprises at least one of polyethylene, polypropylene, polyimide, polytetrafluoroethylene, and polyester.

15. The secondary battery according to any one of claims 1-14, characterized in that, The first tab, the first metal layer, and the second metal layer are connected by riveting or roll welding.

16. The secondary battery according to any one of claims 1-15, characterized in that, The first metal layer and the second metal layer are respectively deposited on opposite surfaces of the first polymer layer by electroplating; Alternatively, the first metal layer and the second metal layer may be deposited on opposite surfaces of the first polymer layer by vapor deposition.

17. An electronic device, characterized in that, Includes the secondary battery as described in any one of claims 1-16.

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