Secondary battery and electronic device

Abstract

The invention relates to a secondary battery and electronic equipment, the secondary battery comprises a first pole piece and a second pole piece which are opposite in polarity, the first pole piece 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, and the first active layer and the second metal layer are arranged along the thickness direction of the first current collector. A first metal layer and a second metal layer are arranged on the two opposite surfaces of the first polymer layer respectively. A first active layer is arranged on the surface, deviating from the first polymer layer, of the first metal layer, the first metal layer is electrically connected with first tabs, the first pole piece is a positive pole piece, the number of the first tabs is N, the thickness of the first metal layer and the thickness of the second metal layer are H1 in the thickness direction of the first current collector, and 1 / N [mu] m < = H1 < = 5 [mu] m. According to the secondary battery and the electronic equipment, the balance between the charge-discharge rate performance and the safety performance of the secondary battery can be improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] As the power source of electronic devices, secondary batteries are the key to ensuring the normal use of electronic devices. In order to improve the energy density and safety performance of secondary batteries, the positive electrode current collector is often designed as a composite current collector (a three-layer sandwich structure of metal layer-polymer layer-metal layer). In order to obtain good charge and discharge rate performance, the metal layer of the composite current collector needs to be thickened, but the thicker the metal layer, the worse the safety performance of the secondary battery. Summary of the invention

[0003] The purpose of the present application is to provide a secondary battery and an electronic device, aiming to improve the balance between the charge and discharge rate performance and the safety performance of the secondary battery.

[0004] According to the first aspect of the present application, a secondary battery is provided, comprising a first pole piece and a second pole piece with opposite polarities, the first pole piece 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, and along the thickness direction of the first current collector, the first metal layer and the second metal layer are respectively arranged on two opposite surfaces of the first polymer layer. The first active layer is arranged on the surface of the first metal layer away from the first polymer layer, the first metal layer is electrically connected to a first pole ear, the first pole piece is a positive pole piece, the number of the first pole ears is N, and 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 H. 1 , 1 / Nμm≤H 1 ≤5μm.

[0005] 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 metal layer and the second metal layer 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 pole ear, and the first pole ear is used to transmit the current of the first pole piece to an external electronic device. The number of the first pole ears is N, and the thickness of the first metal layer and the thickness of the second metal layer is H. 1 In practical applications, the optimal thickness of the first metal layer and the second metal layer is 1 μm when the first current collector is mass-produced, and the first metal layer and the second metal layer of this thickness have good electrical conductivity. 1 ≥1 / Nμm, so that the secondary battery has good charge and discharge rate performance under different numbers of first pole ears. Since increasing the thickness of the first metal layer and the second metal layer will increase the metal burrs caused by mechanical damage to the secondary battery, thus affecting the safety performance of the secondary battery, by limiting H 1≤5μm, so that the secondary battery has good safety performance. In summary, by limiting 1 / Nμm≤H 1 ≤5μm, so that the secondary battery has good charge and discharge rate performance and safety performance when the number of first tabs is different. It should be noted that the thickness of the first metal layer and the second metal layer are both H 1 However, due to process deviations, the thicknesses of the first metal layer and the second metal layer are not necessarily equal.

[0006] In some preferred embodiments, 1.5 / Nμm≤H 1 ≤5μm to further improve the charge and discharge rate performance of secondary batteries.

[0007] In some preferred embodiments, N=1, 1.5 μm≤H 1 ≤3μm. When the number of first pole ears is single, the transmission effect of a single first pole ear on current is poor. In order to improve the charge and discharge rate performance, it is necessary to increase the thickness of the first metal layer and the second metal layer. 1 ≥1.5μm, in order to improve the charge and discharge rate performance of secondary batteries, by limiting H 1 ≤3μm to improve the safety performance of secondary batteries.

[0008] In some preferred embodiments, the thickness of the first polymer layer is H 2 , 2μm≤H 2 ≤12μm. The first polymer layer of the first current collector serves as a support layer to provide mechanical properties. If the thickness of the first metal layer and the second metal layer is H 1 ≥1.5μm, the first metal layer and the second metal layer can also play a role in providing mechanical properties, so the thickness of the first polymer layer can be ≤12μm. In addition, increasing the thickness of the first polymer layer will reduce the energy density of the secondary battery. 2 ≤12μm, so that the first polymer layer has good mechanical properties and the secondary battery has good energy density.

[0009] In some preferred embodiments, the first active layer is provided with a first groove, and the first electrode tab is disposed in the first groove to improve the volume energy density of the secondary battery.

[0010] In some preferred embodiments, N = 2, 1 μm ≤ H 1 ≤3μm. When the number of the first pole tabs is two, the two first pole tabs have a better current transmission effect than a single first pole tab, and the thickness of the first metal layer and the second metal layer can be reduced. 1 ≥1μm, to improve the charge and discharge rate performance of secondary batteries, limit H 1≤3μm to improve the safety performance of secondary batteries.

[0011] In some preferred embodiments, 1 μm ≤ H 1 ≤1.5μm, the thickness of the first polymer layer is H 2 , 2.9μm≤H 2 ≤12μm. If the thickness of the first metal layer and the second metal layer H 1 The first metal layer and the second metal layer can also provide mechanical properties, so the first polymer layer can be thinned. In addition, increasing the thickness of the first polymer layer will reduce the energy density of the secondary battery. 2 ≤12μm, so that the first polymer layer has good mechanical properties and the secondary battery has good energy density.

[0012] In some preferred embodiments, the first active layer is provided with a first groove and a second groove, the first groove and the second groove are arranged at intervals, and two first pole tabs are arranged in the first groove and the second groove respectively to improve the volume energy density of the secondary battery.

[0013] In some preferred embodiments, N ≥ 3, 0.5 μm ≤ H 1 ≤3μm. When the number of the first pole tabs is more than three, the three first pole tabs have a better current transmission effect than the two first pole tabs, and the thickness of the first metal layer and the second metal layer can be reduced. 1 ≥0.5μm, to improve the charge and discharge rate performance of secondary batteries, limit H 1 ≤3μm to improve the safety performance of secondary batteries.

[0014] In some preferred embodiments, 0.5 μm ≤ H 1 ≤1μm, the thickness of the first polymer layer is H 2 , 4.5μm≤H 2 ≤12μm. If the thickness of the first metal layer and the second metal layer H 1 The thickness of the first polymer layer is 0.5 μm to 1 μm, and the thickness of the first polymer layer needs to be increased to increase the mechanical properties. In addition, increasing the thickness of the first polymer layer will reduce the energy density of the secondary battery. 2 ≤12μm, so that the first polymer layer has good mechanical properties and the secondary battery has good energy density.

[0015] In some preferred embodiments, the number of first pole pieces is the same as the number of first pole tabs, and the first metal layer of a first pole piece is connected to a first pole tab. Increasing the number of first pole pieces can reduce the length and width of any first pole piece, thereby improving the charge and discharge rate performance of any first pole piece.

[0016] In some preferred embodiments, the first pole piece includes a second active layer, and the second active layer is disposed on the surface of the second metal layer facing away from the first polymer layer, which can reduce the number of layers of the first pole piece in the secondary battery, thereby improving the energy density.

[0017] In some preferred embodiments, the surface of the first metal layer away from the first polymer layer includes a connected first region and a second region, the first region is provided with a first active layer, the second region is not provided with the first active layer, and the second region is provided with a first pole ear. 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 a second active layer, the fourth region is not provided with a second active layer, and along the thickness direction of the first current collector, the projection of the fourth region on the first metal layer overlaps at least part of the second region. When the first pole ear is provided in the second region, the fourth region can provide a concession space to enhance the convenience of providing the first pole ear in the second region.

[0018] In some preferred embodiments, the first metal layer includes at least one of aluminum, copper, nickel, titanium, silver, and zirconium. And / or the second metal layer includes at least one of aluminum, copper, nickel, titanium, silver, and zirconium.

[0019] In some preferred embodiments, the first polymer layer includes at least one of polyethylene, polypropylene, polyimide, polytetrafluoroethylene, and polyester.

[0020] In some preferred embodiments, the first electrode tab, the first metal layer, and the second metal layer are connected by riveting or roll welding to make the first electrode tab, the first metal layer, and the second metal layer electrically conductive.

[0021] In some preferred embodiments, the first metal layer and the second metal layer are disposed on two opposite surfaces of the first polymer layer by electroplating, or the first metal layer and the second metal layer are disposed on two opposite surfaces of the first polymer layer by evaporation.

[0022] In a second aspect, the present application further proposes an electronic device, comprising a secondary battery as described in any embodiment of the first aspect above.

[0023] The inventors of the present application have found that the secondary battery can improve energy density and safety performance by designing the positive electrode current collector as a composite current collector (a three-layer sandwich structure of metal layer-polymer layer-metal layer). In order to obtain good charge and discharge rate performance, the metal layer of the composite current collector needs to be thickened, but the thicker the metal layer, the worse the safety performance of the secondary battery. For different numbers of pole ears, the charge and discharge rate performance of the secondary battery is different, so the required thickness of the metal layer of the composite current collector is also different. The present application defines the preferred range of the thickness of the metal layer of the first current collector for different numbers of first pole ears to improve the balance between the charge and discharge rate performance and safety performance of the secondary battery.

[0024] Additional aspects and advantages of the embodiments of the present application will be described, shown, or explained in part in the subsequent description through implementation of the embodiments of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] One or more embodiments are exemplarily described by corresponding drawings, which do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings represent similar elements, and unless otherwise stated, the dimensions in the drawings do not constitute proportional limitations.

[0026] Figure 1 A schematic diagram of the structure of a secondary battery in some embodiments of the present application;

[0027] Figure 2 A schematic diagram of the structure of an electrode assembly in some embodiments of the present application;

[0028] Figure 3 A partial schematic diagram of an electrode assembly according to some embodiments of the present application;

[0029] Figure 4 A schematic diagram of the structure of a first pole piece and a first pole ear in some embodiments of the present application;

[0030] Figure 5 This is a schematic structural diagram of the first pole piece and the first pole ear of some embodiments of the present application.

[0031] Description of reference numerals:

[0032] 100. Secondary battery;

[0033] 10. Shell;

[0034] 20. Electrode assembly;

[0035] 21, first pole piece; 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;

[0036] 22, second pole piece; 221, second current collector; 222, third active layer; 223, fourth active layer;

[0037] 23. diaphragm; 24. first pole ear; 25. second pole ear; 26. connecting piece;

[0038] X, first direction. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0040] Reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in conjunction with the embodiment may be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments.

[0041] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0042] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0043] The technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0044] In the first aspect, the embodiment of the present application provides a secondary battery 100, please refer to Figure 1The secondary battery 100 includes a shell 10 and an electrode assembly 20 . The shell 10 can accommodate the electrode assembly 20 and an electrolyte (not shown in the figure). The electrolyte infiltrates the electrode assembly 20 in the shell 10 .

[0045] For the electrode assembly 20, please refer to Figure 2 , Figure 2 The winding structure of the electrode assembly 20 is shown. The electrode assembly 20 includes a first pole piece 21, a diaphragm 23 and a second pole piece 22. The polarities of the first pole piece 21 and the second pole piece 22 are opposite. A diaphragm 23 is arranged between the adjacent second pole piece 22 and the first pole piece 21. The first pole piece 21, the diaphragm 23 and the second pole piece 22 are stacked and wound. Exemplarily, along the thickness direction of the first pole piece 21 and / or the second pole piece 22, the first pole piece 21, the diaphragm 23 and the second pole piece 22 are stacked in sequence and then wound to form a wound electrode assembly 20. In the embodiment of the present application, the electrode assembly 20 is taken as an example for explanation as a winding structure. In some other embodiments, the electrode assembly 20 may also be a laminated structure. For example, along the thickness direction of the first pole piece 21 and / or the second pole piece 22, the first pole piece 21, the diaphragm 23 and the second pole piece 22 are stacked in sequence to form a laminated electrode assembly 20.

[0046] For the first pole piece 21, please refer to Figure 3 The first electrode sheet 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 .

[0047] 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 two opposite surfaces of the first polymer layer 2111. The first active layer 212 is disposed on the surface of the first metal layer 2112 away from the first polymer layer 2111. The first polymer layer 2111 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, and the second metal layer 2113 may include at least one of aluminum, copper, nickel, titanium, silver, and zirconium. The first current collector 211 may be thinned by using the first polymer layer 2111 as the main mechanical support layer, thereby reducing the metal burrs caused by mechanical damage to the secondary battery 100 and reducing the mass of the first current collector 211, thereby improving 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, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0048] In some embodiments, the first metal layer 2112 and the second metal layer 2113 are disposed on opposite surfaces of the first polymer layer 2111 by electroplating. Alternatively, the first metal layer 2112 and the second metal layer 2113 are disposed on opposite surfaces of the first polymer layer 2111 by evaporation.

[0049] As for the first active layer 212, the first active layer 212 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The first active layer 212 includes a first active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and coated on the surface of the first metal layer 2112 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 iron manganese phosphate.

[0050] In some embodiments, the first pole piece 21 includes a second active layer 213 , and the second metal layer 2113 is provided with the second active layer 213 on the surface facing away from the first polymer layer 2111 , which can reduce the number of layers of the first pole piece 21 in the secondary battery 100 , thereby improving the energy density.

[0051] In some embodiments, the first current collector 211 is provided with a first pole tab 24, and the first pole tab 24, the first metal layer 2112, and the second metal layer 2113 are connected by riveting or roll welding to make the first pole tab 24, the first metal layer 2112, and the second metal layer 2113 electrically conductive. In some embodiments, the number of the first pole tab 24 is single or two, and the first pole tab 24, the first metal layer 2112, and the second metal layer 2113 are riveted by a connector 26, for example, the connector 26 penetrates the first metal layer 2112, the first polymer layer 2111, and the second metal layer 2113 and is connected to the first pole tab 24, and the connector 26 can be a rivet.

[0052] In some embodiments, the number of the first electrode tabs 24 is greater than two, and the first electrode tabs 24 , the first metal layer 2112 , and the second metal layer 2113 are connected by roll welding.

[0053] In some embodiments, the surface of the first metal layer 2112 facing away from the first polymer layer 2111 includes a connected first region 211a and a second region 211b, the first region 211a is provided with a first active layer 212, the second region 211b is not provided with the first active layer 212, and the second region 211b is provided with a first pole ear 24, and the first pole ear 24 is used to transmit the current of the first pole piece 21 to an external electronic device. The surface of the second metal layer 2113 facing away from the first polymer layer 2111 includes a connected third region 211c and a fourth region 211d, the third region 211c is provided with a second active layer 213, and the fourth region 211d is not provided with the second active layer 213, and along the thickness direction of the first current collector 211, the projection of the fourth region 211d on the first metal layer 2112 overlaps at least part of the second region 211b. Since the first pole tab 24 needs to be set on the first current collector 211 through a connecting device (such as a welding device), when the first pole tab 24 is set in the second area 211b, part of the connecting device can extend into the second area 211b and the fourth area 211d at the same time to improve the convenience of the connecting device to set the first pole tab 24 in the second area 211b.

[0054] Regarding the second pole piece 22 , the second pole piece 22 includes a second current collector 221 and a third active layer 222 . The second active layer 213 is disposed on the surface of the second current collector 221 facing the first active layer 212 .

[0055] In some embodiments, a fourth active layer 223 is disposed on the surface of the second current collector 221 facing away from the first active layer 212 to reduce the number of layers of the second electrode sheet 22 in the secondary battery 100 , thereby improving the energy density of the secondary battery 100 .

[0056] In some embodiments, please refer to Figure 2The second pole piece 22 is provided with a second pole ear 25, and the second pole ear 25 is used to transmit the current of the second pole piece 22 to an external electronic device.

[0057] For the second current collector 221, the second current collector 221 may be a metal foil, such as a copper foil. The second current collector 221 may 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 a metal layer disposed on two opposite surfaces of the polymer layer, the polymer layer as the main mechanical support layer of the second current collector 221, may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), the metal layer may include at least one of aluminum, copper, nickel, titanium, and silver, the second current collector 221 uses the polymer layer as the main mechanical support layer, the metal layer may be thinned, thereby reducing the metal burrs caused by mechanical damage to the secondary battery 100, and reducing the mass of the second current collector 221, thereby improving the mass energy density of the secondary battery 100. In some other embodiments, the second current collector 221 may be a single-layer metal foil, and the single-layer metal foil may include at least one of aluminum, copper, nickel, titanium, and silver.

[0058] As for the third active layer 222, the third active layer 222 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The third active layer 222 includes a third active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and coated on 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.

[0059] The fourth active layer 223 is infiltrated by the electrolyte in the housing 10 to generate an electrochemical reaction. The fourth active layer 223 includes a fourth active material, a conductive agent, an adhesive, etc. The above materials are mixed and stirred evenly and applied to the surface of the second current collector 221 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.

[0060] In some embodiments, please refer to Figure 2 and Figure 3, the first pole piece 21 is a positive pole piece, and the first metal layer 2112 of the first current collector 211 is electrically connected to the first pole tab 24, and the first pole tab 24 is used to transmit the current of the first pole piece 21 to an external electronic device. In order to obtain good charge and discharge rate performance of the secondary battery 100, the metal layer of the first current collector 211 needs to be thickened, but the thicker the metal layer, the worse the safety performance of the secondary battery 100. For different numbers of pole tabs, the charge and discharge rate performance of the secondary battery 100 is different, so the required thickness of the metal layer of the first current collector 211 is also different.

[0061] To improve the above problem, in the embodiment of the present application, the number of the first tabs 24 is N, and along the thickness direction of the first current collector 211, the thickness of the first metal layer 2112 and the thickness of the second metal layer 2113 are H. 1 , 1 / Nμm≤H 1 ≤5μm. In practical applications, the optimal thickness of the first metal layer 2112 and the second metal layer 2113 is 1μm when the first current collector 211 is mass-produced, and the first metal layer 2112 and the second metal layer 2113 of this thickness have good electrical conductivity. 1 ≥1 / Nμm, so that the secondary battery 100 has good charge and discharge rate performance when the number of first tabs 24 is different. Since increasing the thickness of the first metal layer 2112 and the second metal layer 2113 will increase the metal burrs caused by mechanical damage to the secondary battery 100, thereby affecting the safety performance of the secondary battery 100, by limiting H 1 ≤5μm, so that the secondary battery 100 has good safety performance. In summary, by limiting 1 / Nμm≤H 1 ≤5 μm, so that the secondary battery 100 has good charge and discharge rate performance and safety performance when the number of first tabs 24 is different. It should be noted that the thickness of the first metal layer 2112 and the second metal layer 2113 are both H 1 However, due to process deviations, the thicknesses of the first metal layer 2112 and the second metal layer 2113 are not necessarily equal.

[0062] In some embodiments, 1.5 / N μm ≤ H 1 ≤5μm, so as to further improve the charge and discharge rate performance of the secondary battery 100.

[0063] In some embodiments, N=1, 1.5 μm≤H 1 ≤3μm. When the number of the first pole ear 24 is single, the current transmission effect of the single first pole ear 24 is poor. In order to improve the charge and discharge rate performance, it is necessary to increase the thickness of the first metal layer 2112 and the second metal layer 2113. By limiting H 1 ≥1.5μm, in order to improve the charge and discharge rate performance of the secondary battery 100, by limiting the H1 ≤3μm, so as to improve the safety performance of the secondary battery 100.

[0064] In some embodiments, the thickness of the first polymer layer 2111 is H 2 , 2μm≤H 2 ≤12μm. The first polymer layer 2111 of the first current collector 211 serves as a support layer to provide mechanical properties. If the thickness H of the first metal layer 2112 and the second metal layer 2113 is 1 ≥1.5μm, the first metal layer 2112 and the second metal layer 2113 can also play a role in providing mechanical properties, so the thickness of the first polymer layer 2111 can be ≤12μm. In addition, increasing the thickness of the first polymer layer 2111 will reduce the energy density of the secondary battery 100. By limiting 2μm≤H 2 ≤12 μm, so that the first polymer layer 2111 has good mechanical properties and the secondary battery 100 has good energy density.

[0065] In some embodiments, please refer to Figure 4 The first active layer 212 defines a first groove 2121 , and the first electrode tab 24 is disposed in the first groove 2121 to improve the volume energy density of the secondary battery 100 .

[0066] In some embodiments, N=2, 1 μm≤H 1 ≤3μm. When the number of the first pole tabs 24 is two, the two first pole tabs 24 have a better current transmission effect than a single first pole tab 24, and the thickness of the first metal layer 2112 and the second metal layer 2113 can be reduced. By limiting H 1 ≥1μm, in order to improve the charge and discharge rate performance of the secondary battery 100, limit H 1 ≤3μm, so as to improve the safety performance of the secondary battery 100.

[0067] In some embodiments, 1 μm ≤ H 1 ≤1.5μm, the thickness of the first polymer layer 2111 is H 2 , 2.9μm≤H 2 ≤12μm. If the thickness H of the first metal layer 2112 and the second metal layer 2113 1The first polymer layer 2112 has two functions 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 evaporated onto the first polymer layer 2111 by evaporation 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 a second metal layer 2113 on its surface. Therefore, according to the thickness of the first metal layer 2112 and the second metal layer 2113, Thickness, setting the thickness of the first polymer layer 2111. On the one hand, the first polymer layer 2111 provides mechanical support for the entire first current collector 211; secondly, the first polymer layer 2111 can provide mechanical support for the first current collector 211. Therefore, when the first metal layer 2112 and the second metal layer 2113 are thicker, they can also provide mechanical properties. Therefore, the first polymer layer 2111 can be less than 12μm. In addition, increasing the thickness of the first polymer layer 2111 will reduce the energy density of the secondary battery 100. By limiting 2.9μm≤H 2 ≤12 μm, so that the first polymer layer 2111 will not affect the arrangement of the first metal layer 2112 and the second metal layer 2113, and the secondary battery 100 has good mechanical properties and good energy density.

[0068] In some embodiments, please refer to Figure 5 The first active layer 212 is provided with a first groove 2121 and a second groove 2122 , the first groove 2121 and the second groove 2122 are arranged at intervals, and the two first pole tabs 24 are respectively arranged in the first groove 2121 and the second groove 2122 to improve the volume energy density of the secondary battery 100 .

[0069] In some embodiments, N ≥ 3, 0.5 μm ≤ H 1 ≤3μm. When the number of the first pole tabs 24 is more than three, the three first pole tabs 24 have a better current transmission effect than two first pole tabs 24, and the thickness of the first metal layer 2112 and the second metal layer 2113 can be reduced. By limiting H 1 ≥0.5μm, in order to improve the charge and discharge rate performance of the secondary battery 100, limit H 1 ≤3μm, so as to improve the safety performance of the secondary battery 100.

[0070] In some embodiments, 0.5 μm ≤ H 1 ≤1μm, the thickness of the first polymer layer 2111 is H 2 , 4.5μm≤H 2 ≤12μm. If the thickness H of the first metal layer 2112 and the second metal layer 2113 1The thickness of the first polymer layer 2111 is 0.5 μm to 1 μm, and the thickness of the first polymer layer 2111 needs to be increased to increase the mechanical properties. In addition, increasing the thickness of the first polymer layer 2111 will reduce the energy density of the secondary battery 100. By limiting 4.5 μm≤H 2 ≤12 μm, so that the first polymer layer 2111 has good mechanical properties and the secondary battery 100 has good energy density.

[0071] In some embodiments, the number of first pole pieces 21 is the same as the number of first pole tabs 24, and the first metal layer 2112 of one first pole piece 21 is connected to one first pole tab 24. Increasing the number of first pole pieces 21 can reduce the length and width of any first pole piece 21, thereby improving the charge and discharge rate performance of any first pole piece 21.

[0072] In the second aspect of the present application, an electronic device is also proposed, including a secondary battery 100 as described in any embodiment of the first aspect above. The electronic device of the embodiment of the present application is not particularly limited, and it 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, electric tools, battery cars, electric cars, ships, spacecraft, etc. Among them, electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., and spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0073] Test part:

[0074] 1. Rate performance test of lithium-ion batteries:

[0075] Test process: Tested in an environment of 23±2℃, the battery cell is discharged to 3V at a rate of 0.2C, and then charged to 4.5V at a rate of 0.2C. The discharge and charging process is repeated. The discharge rates are 0.2C, 0.7C, 1.5C, 3C, and 6C to 3V, and charged to 4.5V at 0.2C. The 0.2C discharge capacity after full charge of 4.5V is used as the benchmark, and the subsequent 0.7C, 1.5C, 3C, and 6C discharge capacities are divided by the benchmark value as the rate performance evaluation value.

[0076] 2. Impact test of lithium-ion batteries:

[0077] Test process: In a test environment of 20±5℃, place the sample on the test table with the coding side facing up, and place a round rod with a diameter of 15.8mm at the center of the wide side of the sample, with the round rod 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 and drop it at the intersection of the round rod and the sample. Judgment criteria: no fire or explosion.

[0078] Impact test pass rate = number of passed cells / total number of tested cells.

[0079] Example 1

[0080] <Preparation of positive electrode sheet>:

[0081] The positive electrode active materials lithium cobalt oxide (LiCoO2), carbon black (Super P), and polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97.5:1.0:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%, which is then stirred evenly.

[0082] Polyethylene terephthalate is selected as the polymer layer, and the thickness of the polymer layer is 6μm. Two metal layers of aluminum material with a thickness of 1μm are evaporated on the two surfaces of the polymer layer to obtain a positive current collector. The above slurry is coated on the surface of a metal layer of the positive current collector and a positive empty foil section is reserved. The slurry is dried to obtain a single-sided positive electrode sheet coated with a positive active material layer on one side. On the other metal layer, the above steps are repeated to obtain a double-sided positive electrode sheet coated with a positive active material layer on both sides, and the double-sided positive electrode sheet is provided with a single positive electrode ear.

[0083] <Preparation of negative electrode sheet>:

[0084] Using graphite as the negative electrode active material, the negative electrode active material graphite, the binder styrene butadiene rubber (SBR) and the thickener sodium carboxymethyl cellulose (CMC) are mixed in a weight ratio of 96:2:2, deionized water is added as a solvent, a slurry with a solid content of 70wt% is prepared, and the slurry is stirred evenly.

[0085] Copper foil is selected as the negative electrode current collector, and the above slurry is coated on the surface of the negative electrode current collector and a negative electrode empty foil section is reserved. The slurry is dried to obtain a single-sided negative electrode sheet coated with a negative electrode active material layer on one side. On the other surface of the negative electrode current collector, the above steps are repeated to obtain a double-sided negative electrode sheet coated with a negative electrode active material layer on both sides.

[0086] <Preparation of diaphragm>:

[0087] A polyethylene porous membrane is used as a substrate layer, and a ceramic layer containing alumina ceramics and a PVDF binder is coated on one surface of the substrate layer as a diaphragm (CCS), wherein the mass percentage of the alumina ceramics in the ceramic layer is 95%.

[0088] <Electrolyte Preparation>:

[0089] In a dry argon atmosphere, ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed at a mass ratio of EC:EMC:DEC=30:50:20 to form a basic organic solvent, and then lithium salt lithium hexafluorophosphate (LiPF 6 ) and mixed evenly to obtain LiPF 6 The mass concentration of the electrolyte is 12.5%.

[0090] <Preparation of lithium-ion batteries>:

[0091] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain an electrode assembly. The electrode assembly is placed in an aluminum-plastic film packaging bag, and after drying, the electrolyte is injected, and the lithium-ion battery is obtained through vacuum packaging, static, formation, capacity, degassing, trimming and other processes.

[0092] The relevant parameters in Comparative Examples 1 to 5 and Examples 1 to 26 are shown in Table 1 below.

[0093] The number of positive electrode tabs in Comparative Examples 1 to 3 and Examples 1 to 9 is single, among which, Comparative Examples 2 to 3 and Examples 1 to 5 only differ in the thickness of the metal layer of the positive electrode collector, the thickness of the metal layer and the polymer layer of the positive electrode collector in Comparative Example 1 and Example 9 are adjusted, and Examples 6 to 8 only differ in the thickness of the polymer layer of the positive electrode collector.

[0094] The number of positive electrode tabs in Comparative Example 4 and Examples 10 to 18 are all two, wherein Comparative Example 4 and Examples 10 to 16 only differ in the thickness of the metal layer of the positive electrode current collector, and Examples 17 to 18 only differ in the thickness of the polymer layer of the positive electrode current collector.

[0095] The number of positive electrode tabs in Comparative Example 5 and Examples 19 to 26 are all more than three, wherein Comparative Example 5 and Examples 19 to 24 only differ in the thickness of the metal layer of the positive electrode current collector, and Examples 25 to 26 only differ in the thickness of the polymer layer of the positive electrode current collector.

[0096] Table 1

[0097]

[0098]

[0099] Note: In Table 1, “\” indicates that the parameter is not included, and “*” indicates that the parameter is close to 100%.

[0100] According to Table 1, in combination 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 H of the metal layer of the positive electrode composite current collector is 1<1 / Nμm (where 1μm is the optimal thickness of the metal layer of the positive electrode composite current collector for mass production, and the metal layer of this thickness has good conductivity), the secondary battery has good safety performance, but poor rate performance. 1 >5μm, the secondary battery has good rate performance, but poor safety performance. 1 ≤5μm, compared with comparative examples 1 to 5, the secondary battery can have better rate performance and safety performance.

[0101] Combining 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 H of the metal layer of the positive electrode composite current collector is 1 ≥1.5 / Nμm, the secondary battery can have better rate performance.

[0102] Combining Examples 1 to 5, it can be seen that when the number of positive electrode tabs is single and the thickness of the polymer layer of the positive electrode composite current collector is 6 μm, if the thickness H of the metal layer of the positive electrode composite current collector is 1 <1.5μm, the rate performance of the secondary battery at a 0.2C discharge rate is less than 90%. 1 >3μm, 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 of the metal layer of the positive electrode composite current collector H 1 Preferably, it is 1.5 μm to 3 μm.

[0103] Combining Examples 10 to 16, it can be seen that when the number of positive electrode tabs is two and the thickness of the polymer layer of the positive electrode composite current collector is 6 μm, if the thickness H of the metal layer of the positive electrode composite current collector is 1 <1μm, the rate performance of the secondary battery at a 0.2C discharge rate is less than 90%. 1 >3μm, the impact test pass rate of the secondary battery is less than 80%. Therefore, when the number of positive electrode tabs is two, the thickness of the metal layer of the positive electrode composite current collector H 1 Preferably, it is 1 μm to 3 μm.

[0104] Combining Examples 19 to 24, it can be seen that when the number of positive electrode tabs N is greater than or equal to 3, and the thickness of the polymer layer of the positive electrode composite current collector is 6 μm, if the thickness of the metal layer of the positive electrode composite current collector H is 1 >0.5μm, the rate performance of the secondary battery at a 6C discharge rate is not less than 90%. 1 >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 thickness of the metal layer of the positive electrode composite current collector H 1 It is preferably 0.5 μm to 3 μm.

[0105] Combining Example 20, Example 25 and Example 26, it can be seen that when the thickness H of the metal layer of the positive electrode composite current collector is 1 = 1 μm, if the thickness of the polymer layer of the positive electrode composite current collector H 2 The thickness of the metal layer of the positive electrode composite current collector is 4.5 μm to 12 μm, which has little effect 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 to provide mechanical properties. 1 ≤1μm, thickness of the polymer layer of the positive electrode composite current collector H 2 The thickness of the polymer layer of the positive electrode composite current collector should not be less than 4.5 μm to provide better mechanical properties. 2 If it exceeds 12 μm, the energy density of the secondary battery will be lost. Therefore, when the thickness of the metal layer of the positive electrode composite current collector is 1 When ≤1μm, the thickness of the polymer layer of the positive electrode composite current collector H 2 Preferably, it is 4.5 μm to 12 μm.

[0106] Combining Example 13, Example 17 and Example 18, it can be seen that when the thickness H of the metal layer of the positive electrode composite current collector is 1 = 1.5 μm, if the thickness of the polymer layer of the positive electrode composite current collector H 2 The thickness of the metal layer of the positive electrode composite current collector is 2.9 μm to 12 μm, which has little effect 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 to provide mechanical properties. If the thickness of the metal layer of the positive electrode composite current collector is 1 μm ≤ H 1 ≤1.5μm, the metal layer can also provide mechanical properties, the polymer layer can be thinned, the thickness of the polymer layer H 2 The lower limit of can be reduced from 4.5μm to 2.9μm, while the thickness of the polymer layer of the positive composite current collector H 2 If it exceeds 12 μm, the energy density of the secondary battery will be lost. Therefore, when the thickness of the metal layer of the positive electrode composite current collector is 1 When the thickness H of the polymer layer of the positive electrode composite current collector is 1 μm to 1.5 μm, 2 Preferably, it is 2.9 μm to 12 μm.

[0107] Combining Examples 4 and 6 to 8, it can be seen that when the thickness H of the metal layer of the positive electrode composite current collector is 1 = 3 μm, if the thickness of the polymer layer of the positive electrode composite current collector H 2The thickness of the metal layer of the positive electrode composite current collector is 2 μm to 12 μm, which has little effect 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 to provide mechanical properties. 1 ≥1.5μm, the metal layer can also provide mechanical properties, the polymer layer can be thinned, the thickness of the polymer layer H 2 The lower limit of can be reduced from 2.9μm to 2μm, if H 2 If the thickness is less than 2μm, the impact test pass rate of secondary batteries will be less than 60%, while H 2 If it exceeds 12 μm, the energy density of the secondary battery will be lost. Therefore, when the thickness of the metal layer of the positive electrode composite current collector is 1 When ≥1.5μm, the thickness of the polymer layer of the positive electrode composite current collector H 2 Preferably, it is 2 μm to 12 μm.

[0108] The above descriptions are merely embodiments of the present application and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A secondary battery, comprising a first pole piece and a second pole piece with opposite polarities, wherein the first pole piece comprises a first current collector and a first active layer, wherein the first current collector comprises a first metal layer, a first polymer layer and a second metal layer, wherein along the thickness direction of the first current collector, the first metal layer and the second metal layer are disposed on opposite surfaces of the first polymer layer, respectively; the first active layer is disposed on a surface of the first metal layer away from the first polymer layer, and the first metal layer is electrically connected to a first pole lug; It is characterized in that The first pole piece is a positive pole piece, the number of the first pole tabs is N, and 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, 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, 2 μm≤H2≤12 μm.

5. The secondary battery according to claim 3, characterized in that: The first active layer is provided with a first groove, and the first electrode tab is arranged 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, characterized in that: The first active layer is provided with a first groove and a second groove, the first groove and the second groove are arranged at intervals, and the two first pole tabs are respectively arranged 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: 0.5 μm≤H1≤1 μm, the thickness of the first polymer layer is H2, 4.5 μm≤H2≤12 μm.

11. The secondary battery according to claim 9, characterized in that: The number of the first pole pieces is the same as the number of the first pole lugs, and the first metal layer of each first pole piece is connected to one first pole lug.

12. The secondary battery according to claim 1, characterized in that: The first pole piece includes a second active layer, and the second active layer is disposed on a surface of the second metal layer facing away from the first polymer layer.

13. The secondary battery according to claim 12, characterized in that: The surface of the first metal layer facing away from the first polymer layer includes a first region and a second region connected to each other, 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 electrode tab; The surface of the second metal layer facing 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, the fourth region is not provided with the second active layer, and along the thickness direction of the first current collector, the projection of the fourth region on the first metal layer overlaps with at least part of the second region.

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

15. The secondary battery according to any one of claims 1 to 13, characterized in that: The first electrode tab, the first metal layer and the second metal layer are connected by riveting or roller welding.

16. The secondary battery according to any one of claims 1 to 13, characterized in that: The first metal layer and the second metal layer are respectively disposed on two opposite surfaces of the first polymer layer by electroplating; Alternatively, the first metal layer and the second metal layer are respectively disposed on two opposite surfaces of the first polymer layer by evaporation.

17. An electronic device, characterized in that: Comprising the secondary battery as claimed in any one of claims 1 to 16.

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