Composite current collector and preparation method therefor, battery, and electrical apparatus

Abstract

The present application belongs to the technical field of batteries, and provides a composite current collector and a preparation method therefor, a battery, and an electrical apparatus. The battery comprises an electrode sheet. The electrode sheet comprises a composite current collector, and, in the thickness direction, the composite current collector comprises a base film and a conductive layer formed on at least one side surface of the base film. The composite current collector comprises a main body region and a tab region, and the tensile strength of the main body region is greater than the tensile strength of the tab region. In the present application, the main body region of the composite current collector is provided with a high tensile strength, so that the expansion of an active substance layer can be limited by the composite current collector, thereby inhibiting the overall extension of the electrode sheet, reducing problems such as the composite current collector fracturing, and helping to improve the stability of an electrode structure. Therefore, the present application can improve the stability of a battery.

Description

Composite current collectors and their preparation methods, batteries and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 202411812928.X, filed on December 10, 2024, 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 composite current collector and its preparation method, a battery, and an electrical device. Background Technology

[0004] To meet the demand for long driving range in fields such as electric vehicles, the demand for high-energy-density batteries is increasing. To improve the energy density of batteries, the weight of battery components is usually reduced and the specific capacity of active materials is increased. Component weight reduction can be achieved by using lightweight composite current collectors with polymer films as the main body, while increasing specific capacity can be achieved by using high-specific-capacity materials as active materials.

[0005] However, high-capacity materials expand during battery charging and discharging, which may cause the composite current collector to break and the electrode structure to be damaged, thus affecting the stability of the battery. Summary of the Invention

[0006] In view of the above problems, this application provides a composite current collector and its preparation method, a battery and an electrical device, aiming to improve the stability of the battery.

[0007] In a first aspect, this application provides a battery including an electrode sheet, the electrode sheet including a composite current collector, the composite current collector including a base film and a conductive layer formed on at least one side surface of the base film along the thickness direction; the composite current collector including a body region and a tab region, the tensile strength of the body region being greater than the tensile strength of the tab region.

[0008] In the technical solution of this application embodiment, the main region of the composite current collector is the region where the active material layer is disposed. The tensile strength of the main region is greater than that of the tab region. This allows the main region to withstand the expansion and elongation of the active material layer along the electrode extension direction. In other words, the expansion of the active material layer is restricted by the composite current collector, thereby suppressing the overall elongation of the electrode and reducing problems such as breakage of the composite current collector, thus contributing to improved electrode structure stability. Therefore, this application can improve battery stability.

[0009] In some embodiments, the tensile strength of the main body region is 300MPa-1000MPa; and / or, the tensile strength of the tab region is 100MPa-200MPa.

[0010] In the technical solution of this application embodiment, when the tensile strength of the main body region is between 300MPa and 1000MPa, the composite current collector can significantly suppress the expansion of the active material layer, thereby significantly reducing the elongation of the electrode sheet; the tab region is the area used to connect the external tab, and when the tensile strength of the tab region is between 100MPa and 200MPa, it can increase the weldability window, reduce the difficulty of roll welding, and help improve the welding pull force.

[0011] In some embodiments, the base membrane includes membrane I and membrane II connected together, membrane I being disposed corresponding to the main body region, and membrane II being disposed corresponding to the tab region, wherein the tensile strength of membrane I is greater than the tensile strength of membrane II.

[0012] In the technical solution of this application embodiment, by selecting membrane I and membrane II with different tensile strengths to form the base membrane, the tensile strength of the composite current collector body region can be greater than the tensile strength requirement of the tab region. Moreover, changing the tensile strength of membrane I and membrane II to change the tensile strength of the body region and the tab region has the advantage of being easy to control.

[0013] In some embodiments, the membrane II satisfies at least one of the following conditions: the melting point of the membrane material of the membrane II is 200°C; the polymer backbone of the membrane material of the membrane II is a carbon chain.

[0014] In the technical solution of this application embodiment, the melting point of the membrane II material is between 200°C and 300°C. It is prone to deformation during welding, resulting in greater friction and thus increasing welding strength. When the polymer backbone of the membrane II material is a carbon chain, it exhibits high stability and is less prone to reaction, reducing the risk of electrolyte corrosion of the base film from the side, thereby improving battery reliability.

[0015] In some embodiments, the membrane material of membrane I includes at least one of polyimide, high molecular weight polypropylene, polyethylene terephthalate, and polyimide-polypropylene copolymer; and / or, the membrane material of membrane II includes at least one of polyethylene and low molecular weight polypropylene.

[0016] In the technical solutions of this application, the main chain of polyimide is typically composed of structural units such as benzene rings and imide rings, which have high bond energy and intramolecular conjugation effect, thus endowing polyimide with high stability and strength. The main chains of polyethylene and low molecular weight polypropylene are composed of carbon-carbon single bonds, which can rotate freely, making the molecular chains easily deformable under stress; therefore, polyethylene and low molecular weight polypropylene have relatively weak strength.

[0017] In some embodiments, the degree of polymerization n1 of polyimide and the degree of polymerization n2 of polypropylene in the polyimide-polypropylene copolymer satisfy n1:n2=(7-9):(1-3).

[0018] In the technical solution of this application embodiment, setting the proportion of polyimide in the polyimide-polypropylene copolymer to be greater than or equal to 70% can make the polyimide-polypropylene copolymer have higher strength.

[0019] In some embodiments, the polyimide includes at least a biphenyl polyimide, wherein the biphenyl polyimide accounts for 70%-100% of the total polyimide by mass.

[0020] In the technical solution of this application embodiment, the biphenyl-type polyimide has high strength. Therefore, setting the mass ratio of biphenyl-type polyimide in polyimide to 70%-100% helps to obtain a polyimide film material with higher strength.

[0021] In some embodiments, the thickness of membrane I is greater than or equal to the thickness of membrane II.

[0022] In the technical solution of this application embodiment, when the thickness of film I is equal to the thickness of film II, a flat base film surface can be formed, which is beneficial to improving the uniformity of the conductive layer; while when the thickness of film II is less than the thickness of film I, in order to form a flat composite current collector surface, the thickness of the conductive layer of film II will be greater than the thickness of the conductive layer of film I, which is beneficial to conductivity and welding.

[0023] In some embodiments, the thickness difference between membrane I and membrane II is 0 μm-0.5 μm.

[0024] In the technical solution of this application embodiment, when the thickness difference between membrane I and membrane II is 0μm-0.5μm, it is beneficial for the winding of the composite current collector.

[0025] In some embodiments, the thickness of membrane I is 3 μm-7 μm.

[0026] In the technical solution of this application embodiment, when the thickness of membrane I is between 3μm and 7μm, it helps to improve the strength of the composite current collector.

[0027] In some embodiments, the base membrane further includes membrane III, which is disposed on opposite sides of membrane I, and membrane III is disposed corresponding to the main body region.

[0028] In the technical solution of this application embodiment, when the membrane material of membrane I contains amide or other groups, it is easy to react and decompose. Membrane II and membrane III can protect membrane I from corrosion and decomposition by electrolyte, thereby improving the reliability of the battery.

[0029] In some embodiments, the width of membrane III is 1 mm to 5 mm.

[0030] In the technical solution of this application embodiment, when the width of membrane III is between 1mm and 5mm, it can not only have a certain protective effect, but also reduce the impact on the overall strength of the base membrane.

[0031] In some embodiments, the membrane material of membrane III includes at least one of polyethylene and low molecular weight polypropylene.

[0032] In the technical solution of this application embodiment, polyethylene and low molecular weight polypropylene have high stability in the electrolyte and are not easily corroded or decomposed.

[0033] In some embodiments, along the thickness direction, the composite current collector further includes a metal adhesive layer disposed between the base film and the conductive layer.

[0034] In the technical solution of this application embodiment, the metal adhesive layer can form a metal bond with the conductive layer, thereby improving the bonding strength of the conductive layer.

[0035] In some embodiments, the thickness of the metal adhesive layer is 50nm-150nm.

[0036] In the technical solution of this application embodiment, when the thickness of the metal adhesive layer is between 50nm and 150nm, it can not only make the metal adhesive layer have high adhesion and reduce the problem of uneven coating of conductive layer, but also reduce the problem of battery energy density being affected by the overall thickness of composite current collector being too thick.

[0037] In some embodiments, the metal adhesive layer includes at least one of nickel, iron, chromium, and cobalt.

[0038] In the technical solution of this application embodiment, the above-mentioned elements are not only easy to plate, but also have good affinity with the conductive layer.

[0039] In some embodiments, the thickness of the conductive layer is 0.5 μm-1.5 μm.

[0040] In the technical solution of this application embodiment, when the thickness of the conductive layer is between 0.5μm and 1.5μm, it not only enables the composite current collector to have a lighter weight and improves the battery energy density, but also reduces the impact on overcurrent and improves battery power.

[0041] In some embodiments, the conductive layer comprises at least one of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0042] In the technical solution of this application embodiment, the above-mentioned metal not only has high electrical conductivity, but also has a certain strength and toughness, which can withstand the tension and pressure that may be generated during battery assembly and use to a certain extent.

[0043] In some embodiments, the tab area is provided with a solder mark area, and the solder mark area is 1mm-5mm away from the junction of the tab area and the body area.

[0044] In the technical solution of this application embodiment, when the distance between the soldering area and the junction of the tab area and the main body area is between 1mm and 5mm, the situation of base film breakage and poor welding during welding can be reduced.

[0045] In some embodiments, the composite current collector further includes an external electrode tab, which is disposed corresponding to the solder area of ​​the electrode tab region.

[0046] In the technical solution of this application embodiment, the external electrode can be selected with materials having lower resistance and a more optimized structure as needed, thereby reducing energy loss during current transmission. Compared with directly leading the electrode out of the composite current collector, the external electrode can effectively reduce the contact resistance between the current collector and the electrode, as well as the resistance of the electrode itself.

[0047] In some embodiments, the electrode further includes an active material layer, which is disposed at least on one side surface of the composite current collector and covers the junction between the main body region and the tab region.

[0048] In the technical solution of this application embodiment, the active material layer covers the junction between the main body area and the tab area, which helps to improve the connection strength between membrane I and membrane II, thereby reducing the possibility of base membrane breakage or poor welding during tab welding.

[0049] Secondly, this application provides a method for preparing a composite current collector, comprising:

[0050] A base film is provided, the base film comprising a connected film I and a film II, wherein the tensile strength of film I is greater than the tensile strength of film II; a conductive layer is coated on at least one surface of the base film; and tabs are provided on the surface of the conductive layer at locations corresponding to film II.

[0051] In some embodiments, "providing a base film" includes:

[0052] Membrane I and membrane II are connected together; the connection between membrane I and membrane II is subjected to heat fusion treatment, and after cooling, membrane I and membrane II are connected to form a base membrane.

[0053] In the technical solution of this application embodiment, the hot melt treatment can form a continuous whole at the junction of membrane I and membrane II, so that the junction has a high bonding force, thereby improving the overall stability of the base membrane.

[0054] In some embodiments, the step of “providing tabs on the surface of the conductive layer corresponding to the film II” includes: with conductive layers covering both sides of the base film, providing a first tab on one side of the conductive layer surface and a second tab on the other side of the conductive layer surface, electrically connecting the first tab and the second tab, and welding the first tab / second tab to the conductive layer.

[0055] In the technical solution of this application embodiment, by setting the first tab and the second tab, the composite current collector can be made to conduct on both sides, thereby improving the current carrying capacity of the composite current collector and reducing the overall resistance of the composite current collector; in addition, the tab structure can improve the reliability of the connection and reduce the risk of increased resistance and heat generation caused by poor connection.

[0056] In some embodiments, the lengths of the first electrode and the second electrode are different.

[0057] In the technical solution of this application embodiment, setting one side of the electrode tab to a short electrode tab is to reduce the total number of electrode tab layers and reduce the problem of incomplete soldering during subsequent welding.

[0058] Thirdly, this application provides a composite current collector, which is prepared by any of the above-mentioned preparation methods.

[0059] Fourthly, this application provides an electrical device including any of the batteries described above.

[0060] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0061] Figure 1 is a schematic diagram of the vehicle structure in some embodiments of this application;

[0062] Figure 2 is a schematic diagram of the exploded structure of the battery in some embodiments of this application;

[0063] Figure 3 is a schematic diagram of the exploded structure of a single battery cell in some embodiments of this application;

[0064] Figure 4 is a cross-sectional schematic diagram of the electrode sheet in some embodiments of this application;

[0065] Figure 5 is a schematic diagram of the base film in some other embodiments of this application;

[0066] Figure 6 is a schematic diagram of the base film in some embodiments of this application;

[0067] Figure 7 is a schematic diagram of the electrode sheets in some embodiments of this application;

[0068] Figure 8 is a schematic diagram of the electrode in some other embodiments of this application.

[0069] Figure Descriptions: Vehicle 1000; Battery unit 100, controller 200, motor 300; Housing 10, first part 11, second part 12; Battery cell 20, end cap 21, housing 22, electrode assembly 23, composite current collector 231, base film 2311, film I 2311-1, film II 2311-2, film III 2311-3, conductive layer 2312, metal bonding layer 2313, external tab 2314, first tab 2314-1, second tab 2314-2. Detailed Implementation

[0070] The following embodiments are only used to illustrate the technical solutions of this application more clearly, and are therefore only examples and should not be used to limit the scope of protection of this application.

[0071] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0072] 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.

[0073] In this document, the term "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 throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0074] 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.

[0075] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). The term "at least one" refers to one or more.

[0076] Composite current collectors typically consist of a polymer substrate in the middle and conductive metal layers on both sides. The polymer substrate is lighter than conventional metal foil current collectors, contributing to a lighter battery. High-specific-capacity materials refer to materials with high specific capacity, meaning they can store more electrical energy per unit mass. Common high-specific-capacity materials used for negative electrode active materials include silicon and tin. Therefore, using composite current collectors and high-specific-capacity materials can improve the energy density of the battery.

[0077] However, during battery charging and discharging, lithium ions intercalate into the silicon anode to form an alloy, causing a significant volume change in the silicon lattice. This leads to expansion of the silicon anode; in a fully lithium-intercalated state, the volume expansion rate of silicon can reach over 300%, and the same applies to tin anodes. Severe high expansion of the anode material can cause the composite current collector to fracture, leading to electrode structure damage and affecting battery stability.

[0078] To address the aforementioned issues, a battery is designed and disclosed, wherein the electrode includes a composite current collector, which comprises a main body region and a tab region, and the tensile strength of the main body region is greater than the tensile strength of the tab region.

[0079] In such a battery, the main region is the area where the active material layer is set. The main region refers to the region with high tensile strength, which can withstand the expansion of the active material layer, thereby suppressing the overall extension of the electrode sheet, reducing problems such as the breakage of the composite current collector, and helping to improve the stability of the electrode structure.

[0080] The batteries disclosed in this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. The power system of such electrical devices can also be composed of batteries disclosed in this application.

[0081] This application provides an electrical device that uses a battery as a power source. The electrical device can be, but is not limited to, 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. Spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0082] For ease of explanation, the following embodiments will be described using a vehicle 1000 as an example of an electrical device according to an embodiment of this application.

[0083] Referring to Figure 1, vehicle 1000 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A battery 100 is installed inside vehicle 1000, which can be located at the bottom, front, or rear of vehicle 1000. Battery 100 can be used to power vehicle 1000; for example, battery 100 can serve as the operating power source for vehicle 1000. Vehicle 1000 may also include a controller 200 and a motor 300. Controller 200 controls the battery 100 to supply power to motor 300, for example, to meet the power needs of vehicle 1000 during starting, navigation, and driving.

[0084] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0085] In some embodiments of this application, the battery 100 may be a battery cell, a battery module, or a battery pack. Referring to FIG2, the battery 100 is described as a battery module. The battery 100 may include a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10. The housing 10 provides a space for accommodating the battery cell 20, and the housing 10 may adopt various structures. In some embodiments, the housing 10 may include a first portion 11 and a second portion 12, which overlap each other, and the first portion 11 and the second portion 12 together define an accommodating space for accommodating the battery cell 20. The second portion 12 may be a hollow structure with one end open, and the first portion 11 may be a plate-like structure, with the first portion 11 covering the open side of the second portion 12 so that the first portion 11 and the second portion 12 together define the accommodating space; the first portion 11 and the second portion 12 may also be hollow structures with one side open, with the open side of the first portion 11 covering the open side of the second portion 12. Of course, the box 10 formed by the first part 11 and the second part 12 can be of various shapes, such as a cylinder, a cuboid, etc.

[0086] In battery 100, there can be multiple battery cells 20, which can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel configurations. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the entire assembly of the multiple battery cells 20 is housed within the housing 10. Alternatively, battery 100 can also be composed of multiple battery cells 20 first connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules are connected in series, parallel, or in a mixed manner to form a whole, which is also housed within the housing 10. Battery 100 may also include other structures; for example, it may include a busbar component for electrical connection between the multiple battery cells 20.

[0087] Each battery cell 20 can be a secondary battery or a primary battery; it can also be a lithium-sulfur battery, a sodium-ion battery, or a magnesium-ion battery, but is not limited to these. The battery cell 20 can be cylindrical, flat, cuboid, or other shapes.

[0088] Referring to Figure 3, the battery cell 20 refers to the smallest unit that makes up the battery. The battery cell 20 includes an end cap 21, a housing 22, an electrode assembly 23, and other functional components.

[0089] End cap 21 refers to a component that covers the opening of housing 22 to isolate the internal environment of battery cell 20 from the external environment. The shape of end cap 21 can be adapted to the shape of housing 22 to fit it. Optionally, end cap 21 can be made of a material with certain hardness and strength (such as aluminum alloy), so that end cap 21 is not easily deformed under pressure or impact, allowing battery cell 20 to have higher structural strength. Functional components such as electrode terminals can be provided on end cap 21. Electrode terminals can be used for electrical connection with electrode assembly 23 for outputting or inputting electrical energy into battery cell 20. In some embodiments, end cap 21 can also be provided with a pressure relief mechanism for releasing internal pressure when the internal pressure or temperature of battery cell 20 reaches a threshold. The material of end cap 21 can also be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc., and this application embodiment does not impose any special limitations on this. In some embodiments, an insulating element may be provided on the inner side of the end cap 21. The insulating element can be used to isolate the electrical connecting pieces inside the housing 22 from the end cap 21 to reduce the risk of short circuit. For example, the insulating element may be made of plastic, rubber, etc.

[0090] The housing 22 is a component used to cooperate with the end cap 21 to form the internal environment of the battery cell 20. This internal environment can accommodate the electrode assembly 23, electrolyte, and other components. The housing 22 and the end cap 21 can be independent components. An opening can be provided on the housing 22, and the end cap 21 can be used to close the opening to form the internal environment of the battery cell 20. Alternatively, the end cap 21 and the housing 22 can be integrated. Specifically, the end cap 21 and the housing 22 can form a common connecting surface before other components are inserted into the housing. When it is necessary to encapsulate the interior of the housing 22, the end cap 21 closes the housing 22. The housing 22 can be of various shapes and sizes, such as cuboid, cylindrical, hexagonal prism, etc. Specifically, the shape of the housing 22 can be determined according to the specific shape and size of the electrode assembly 23. The material of the housing 22 can be various, such as copper, iron, aluminum, stainless steel, aluminum alloy, plastic, etc. This application embodiment does not impose any special limitations on this.

[0091] Electrode assembly 23 is the component in the battery cell 20 where electrochemical reactions occur. The casing 22 may contain one or more electrode assemblies 23. The electrode assembly 23 is mainly formed by winding or stacking positive and negative electrode sheets, and typically a separator is provided between the positive and negative electrode sheets. The portions of the positive and negative electrode sheets containing active material constitute the main body of the electrode assembly, while the portions without active material each constitute a tab. The positive and negative tabs may be located together at one end of the main body or separately at both ends. During the charging and discharging process of the battery, the positive and negative active materials react with the electrolyte, and the tabs connect to the electrode terminals to form a current loop.

[0092] Of course, in some other embodiments, the battery 100 may also be integrated with the chassis / body.

[0093] According to some embodiments of this application, this application provides a battery 100, which includes at least one battery cell 20. The battery cell 20 includes an electrode, and the electrode includes a composite current collector 231. Referring to FIG4, along the thickness direction, the composite current collector 231 includes a base film 2311 and a conductive layer 2312 formed on at least one side surface of the base film 2311. The composite current collector 231 includes a body region and a tab region, and the tensile strength of the body region is greater than the tensile strength of the tab region.

[0094] The electrode includes a positive electrode and / or a negative electrode. Specifically, the positive electrode may include a composite current collector 231, the negative electrode may include a composite current collector 231, or both the positive and negative electrodes may include a composite current collector 231.

[0095] The main body region refers to the area on the composite current collector 231 where the active material layer is disposed, and the tab region refers to the area on the composite current collector 231 used to connect external tabs. Taking Figure 4 as an example, the tab region is located on the left side of the main body region.

[0096] Tensile strength, also known as tensile breaking strength, refers to the maximum stress value that the membrane material can withstand when it breaks during stretching. Setting the tensile strength of the main body region to be greater than that of the tab region, meaning the main body region has higher tensile strength, allows it to withstand the expansion and elongation of the active material layer along the electrode extension direction. This restricts the expansion of the active material layer by the composite current collector 231, thereby suppressing the overall elongation of the electrode and reducing the risk of breakage of the composite current collector, thus contributing to improved electrode structure stability. Therefore, this application can improve battery stability.

[0097] According to some embodiments of this application, the tensile strength of the main body region is 300MPa-1000MPa; and / or, the tensile strength of the tab region is 100MPa-200MPa.

[0098] When the tensile strength of the main body region is between 300 MPa and 1000 MPa, the composite current collector 231 can significantly suppress the expansion of the active material layer, thereby significantly reducing the elongation of the electrode sheet. When the tensile strength of the tab region is between 100 MPa and 200 MPa, it can increase the weldability window, reduce the difficulty of roll welding, and help improve the welding tensile strength.

[0099] According to some embodiments of this application, the base membrane 2311 includes membrane I 2311-1 and membrane II 2311-2 connected together. Membrane I 2311-1 is disposed in the main body region, and membrane II 2311-2 is disposed in the tab region. The tensile strength of membrane I 2311-1 is greater than the tensile strength of membrane II 2311-2.

[0100] Taking Figure 5 as an example, membrane I 2311-1 corresponds to the main body region, and membrane II 2311-2 corresponds to the tab region, meaning that membrane I 2311-1 is located to the right of membrane II 2311-2. By selecting membranes I 2311-1 and II 2311-2 with different tensile strengths to form the base membrane 2311, the tensile strength of the main body region of the composite current collector 231 can be greater than the tensile strength requirement of the tab region. Furthermore, changing the tensile strength of membranes I 2311-1 and II 2311-2 to change the tensile strength of the main body region and the tab region has the advantage of easy control.

[0101] According to some embodiments of this application, membrane II 2311-2 satisfies at least one of the following conditions: the melting point of the membrane material of membrane II 2311-2 is less than 200°C; the polymer backbone of the membrane material of membrane II 2311-2 is a carbon chain.

[0102] The melting point of a membrane material refers to the temperature at which it changes from a solid to a liquid state. When the melting point of the membrane material II 2311-2 is less than 200℃, the membrane material II 2311-2 is prone to deformation during welding, which generates greater friction and helps to increase the welding strength.

[0103] The polymer backbone of the membrane material is a carbon chain, which means that the polymer backbone is connected by carbon-carbon bonds and does not contain other groups. The saturated carbon-carbon single bonds have high bond energy, are not easy to break, have high stability, and are not easy to react. Therefore, it can reduce the corrosion of the base film by the electrolyte from the side, thereby improving the reliability of the battery.

[0104] According to some embodiments of this application, the membrane material of membrane I2311-1 includes at least one of polyimide, high molecular weight polypropylene, polyethylene terephthalate, and polyimide-polypropylene copolymer; and / or, the membrane material of membrane II2311-2 includes at least one of polyethylene and low molecular weight polypropylene.

[0105] Polyimide (PI) is typically synthesized from dianhydrides and diamines via a condensation reaction. Its main chain is usually composed of aromatic rings, imide rings, and other structural units. These cyclic structures possess high bond energies and intramolecular conjugation effects, thus endowing polyimide with high stability and tensile strength. Furthermore, various strong intermolecular forces exist between polyimide molecules, resulting in tight bonding between the molecular chains, which also contributes to the high tensile strength of polyimide.

[0106] Polypropylene (PP) refers to polypropylene with a weight-average molecular weight greater than 50w. Films made of polypropylene with a molecular weight greater than 50w usually have higher tensile strength. This is because polypropylene is a linear polymer. When the molecular weight increases, the molecular chains become longer and the entanglement between the molecular chains becomes tighter. More force is required to cause the molecular chains to slip and break, so the tensile strength is higher.

[0107] Polyethylene terephthalate (PET) is a thermoplastic material formed by the polycondensation reaction of terephthalic acid and ethylene glycol. Its molecular chain contains a rigid benzene ring structure, so PET has high tensile strength.

[0108] Polyimide-polypropylene copolymer refers to a polymer formed by copolymerizing polyimide monomers with polypropylene monomers. The addition of polyimide chains significantly improves its tensile strength.

[0109] The main chains of polyethylene and low molecular weight polypropylene (weight average molecular weight less than 50w) are composed of carbon-carbon single bonds. These carbon-carbon single bonds can rotate freely, making the molecular chains easily deformable under stress. Therefore, polyethylene and polypropylene have relatively weak tensile strength.

[0110] According to some embodiments of this application, the degree of polymerization n1 of polyimide and the degree of polymerization n2 of polypropylene in the polyimide-polypropylene copolymer satisfy n1:n2=(7-9):(1-3).

[0111] The degree of polymerization of polyimide, n1, refers to the proportion of polyimide chains in the polyimide-polypropylene copolymer, while the degree of polymerization of polypropylene, n2, refers to the proportion of polypropylene chains in the polyimide-polypropylene copolymer. Since polyimide chains have high strength, setting the proportion of polyimide in the polyimide-polypropylene copolymer to be greater than or equal to 70% can make the polyimide-polypropylene copolymer have high tensile strength.

[0112] According to some embodiments of this application, the polyimide includes at least a biphenyl polyimide, wherein the biphenyl polyimide accounts for 70%-100% of the mass of the polyimide.

[0113] Biphenyl-type polyimide refers to polyimide whose main chain structure contains a biphenyl structure. It is usually formed by the polycondensation reaction of biphenyl dianhydride and diamine. The introduction of the biphenyl structure greatly increases the rigidity of the molecular main chain.

[0114] Biphenyl-type polyimides have high strength, so setting the mass ratio of biphenyl-type polyimides in polyimides to 70%-100% helps to obtain polyimide films with higher strength.

[0115] In some embodiments, biphenyl polyimide and pyromellitic polyimide can be used in combination. Pyromellitic polyimide is a polymer formed by the polycondensation reaction of pyromellitic dianhydride and diamine. Its molecular backbone consists of alternating imide rings and benzene rings. This structure makes the molecular chain difficult to rotate and bend, which helps to improve the tensile strength of the membrane material I2311-1.

[0116] According to some embodiments of this application, the thickness of membrane I2311-1 is greater than or equal to the thickness of membrane II2311-2.

[0117] When the thickness of membrane I2311-1 is equal to the thickness of membrane II2311-2, a smooth base film surface can be formed, which is beneficial to improving the uniformity of the conductive layer. However, when the thickness of membrane II2311-2 is less than the thickness of membrane I2311-1, in order to form a smooth composite current collector surface, the thickness of the conductive layer of membrane II2311-2 will be greater than the thickness of the conductive layer of membrane I2311-1, which is beneficial to conductivity and welding.

[0118] According to some embodiments of this application, the thickness difference between membrane I 2311-1 and membrane II 2311-2 is 0 μm-0.5 μm. A thickness difference of 0 μm-0.5 μm between membrane I 2311-1 and membrane II 2311-2 is beneficial for the winding of the composite current collector 231.

[0119] According to some embodiments of this application, the thickness of membrane I2311-1 is 3μm-7μm.

[0120] For example, the thickness of membrane I2311-1 can be 3μm, 4μm, 5μm, 6μm or 7μm. When the thickness of membrane I2311-1 is between 3μm and 7μm, it helps to improve the strength of composite current collector 231.

[0121] When the thickness of membrane I2311-1 is 3 μm, the thickness of membrane II2311-2 can be 3 μm, 2.7 μm, or 2.5 μm; when the thickness of membrane I2311-1 is 4 μm, the thickness of membrane II2311-2 can be 4 μm, 3.8 μm, or 3.5 μm; when the thickness of membrane I2311-1 is 5 μm, the thickness of membrane II2311-2 can be 5 μm, 4.7 μm, or 4.5 μm; when the thickness of membrane I2311-1 is 6 μm, the thickness of membrane II2311-2 can be 6 μm, 5.8 μm, or 5.5 μm; when the thickness of membrane I2311-1 is 7 μm, the thickness of membrane II2311-2 can be 7 μm, 6.8 μm, or 6.5 μm.

[0122] According to some embodiments of this application, as shown in FIG6, the base membrane 2311 further includes membrane III 2311-3, which is disposed on both sides of membrane I 2311-1, and membrane III 2311-3 is disposed in relation to the main body area.

[0123] When polyimide is selected as the membrane material for membrane I 2311-1, polyimide contains amide groups, which are prone to reaction and decomposition. Membranes II 2311-2 and III 2311-3 can protect membrane I 2311-1 from corrosion and decomposition by the electrolyte, thereby improving the reliability of the battery.

[0124] According to some embodiments of this application, the width of membrane III2311-3 is 1mm-5mm.

[0125] For example, the width of membrane III2311-3 can be 1mm, 2mm, 3mm, 4mm or 5mm. When the width of membrane III 2311-3 is between 1mm and 5mm, it can not only provide a certain protective effect, but also reduce the impact on the overall strength of the base membrane 2311.

[0126] According to some embodiments of this application, the membrane material of membrane III2311-3 includes at least one of polyethylene and low molecular weight polypropylene. Polyethylene and low molecular weight polypropylene have high stability in electrolytes and are not easily corroded or decomposed.

[0127] According to some embodiments of this application, as shown in FIG4, along the thickness direction, the composite current collector 231 further includes a metal adhesive layer 2313, which is disposed between the base film 2311 and the conductive layer 2312.

[0128] The metal bonding layer 2313 refers to a metal layer that can improve the bonding strength between the base film 2311 and the conductive layer 2312. The metal bonding layer 2313 can form a metal bond with the conductive layer 2312, thereby improving the bonding strength of the conductive layer 2312.

[0129] According to some embodiments of this application, the thickness of the metal adhesive layer 2313 is 50nm-150nm.

[0130] For example, the thickness of the metal adhesive layer 2313 can be 50nm, 60nm, 70nm, 80nm, 100nm, 120nm or 150nm. When the thickness of the metal adhesive layer 2313 is between 50nm and 150nm, it can not only make the metal adhesive layer have high adhesion and reduce the problem of uneven coating of conductive layer, but also reduce the problem of battery energy density being affected by the overall thickness of composite current collector.

[0131] According to some embodiments of this application, the metal adhesive layer 2313 includes at least one selected from nickel, nickel alloy, iron, iron alloy, chromium, chromium alloy, cobalt, and cobalt alloy. These elements are easy to plate and have high affinity for the conductive layer.

[0132] According to some embodiments of this application, the thickness of the conductive layer 2312 is 0.5μm-1.5μm.

[0133] For example, the thickness of the conductive layer 2312 can be 0.5μm, 0.7μm, 1.0μm, 1.3μm or 1.5μm. When the thickness of the conductive layer is between 0.5μm and 1.5μm, not only can the composite current collector 231 have a lighter weight and improve the battery energy density, but it can also reduce the impact on overcurrent and improve the battery power.

[0134] According to some embodiments of this application, the conductive layer 2312 includes at least one of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0135] When the composite current collector 231 is used on the positive electrode, the conductive layer 2312 can be at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. When the composite current collector 231 is used on the negative electrode, the conductive layer 2312 can be at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

[0136] The aforementioned metals not only have high electrical conductivity, but also a certain degree of strength and flexibility, enabling them to withstand the tension and pressure that may occur during battery assembly and use to a certain extent.

[0137] According to some embodiments of this application, the tab area is provided with a soldering area, and the soldering area is 1mm-5mm away from the junction of the tab area and the main body area.

[0138] The soldering area refers to the area for welding and fixing the external electrode tab. For example, the distance between the soldering area and the junction of the electrode tab area and the main body area can be 1mm, 2mm, 3mm, 4mm or 5mm, which can reduce the situation of base film breakage and poor welding during welding.

[0139] According to some embodiments of this application, referring to FIG7, the composite current collector 231 further includes an external tab 2314, which is disposed in the solder area of ​​the tab region.

[0140] The external tab 2314 can be set to one or two. When two external tabs 2314 are set, the two external tabs 2314 are respectively located on both sides of the base film 2311, and the two external tabs 2314 are electrically connected.

[0141] The external tab 2314 can be made of materials with lower resistance and have a more optimized structure, thereby reducing energy loss during current transmission. Compared to directly leading the tab out of the composite current collector 231, the external tab 2314 can effectively reduce the contact resistance between the composite current collector and the electrode, as well as the resistance of the tab itself.

[0142] According to some embodiments of this application, as shown in FIG4, the electrode further includes an active material layer 232, which is disposed at least on one side surface of the composite current collector 231, and covers the junction of the main body region and the tab region.

[0143] When the electrode is a positive electrode, the active material layer 232 is a positive active material layer, which includes a positive active material. When the battery is a lithium-ion battery, the positive active material can be a positive active material known in the art for lithium-ion batteries. As an example, the positive active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0144] In some embodiments, the positive electrode active material layer may optionally include a binder. For example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0145] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. For example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0146] When the electrode is a negative electrode, the active material layer 232 is a negative electrode active material layer, which includes a negative electrode active material. This negative electrode active material can be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. The silicon-based material may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys.

[0147] In some embodiments, the negative electrode active material layer may optionally include a binder. As an example, the binder may include at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0148] In some embodiments, the negative electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0149] In some embodiments, the negative electrode active material layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0150] The junction of the active material layer 232 covering the main body area and the tab area can also refer to the interface between membrane I2311-1 and membrane II2311-2 located in the coating area of ​​the active slurry. This helps to improve the connection strength between membrane I2311-1 and membrane II2311-2, thereby reducing the possibility of the base membrane 2311 breaking or poor welding during tab welding.

[0151] According to some embodiments of this application, this application also provides a method for preparing a composite current collector, comprising: providing a base membrane, the base membrane comprising a membrane I and a membrane II connected together, wherein the tensile strength of the membrane material of membrane I is greater than the tensile strength of the membrane material of membrane II; covering at least one side surface of the base membrane with a conductive layer; and providing tabs on the surface of the conductive layer at locations corresponding to membrane II.

[0152] When a conductive layer is coated on at least one side of a base film, methods such as vacuum evaporation, magnetron sputtering, electroless plating, or electroplating can be used. Vacuum evaporation involves heating the conductive metal to its evaporation temperature in a vacuum environment, causing it to vaporize and deposit on the base film surface to form a conductive layer. This method can create a thin and uniform conductive layer with good adhesion to the base film. Magnetron sputtering uses high-energy particles to bombard a conductive metal target, causing metal atoms to sputter from the target surface and deposit on the base film surface to form a conductive layer. This method can be performed at relatively low temperatures with minimal damage to the base film. Electroless plating involves immersing the surface-treated base film in an electroless plating solution containing conductive metal ions. Under the action of a catalyst, the metal ions are reduced and deposited on the base film surface to form a conductive layer, making it suitable for base films with complex shapes. Electroplating uses direct current to reduce conductive metal ions from the plating solution and deposit them on the base film surface, which serves as the cathode, to form a conductive layer. The base film needs to be conductively treated before electroplating. This method has the advantages of high deposition rates and the ability to produce thicker conductive layers.

[0153] When tabs are placed on the surface of the conductive layer corresponding to film II, a welding process is usually used. The welding process can be roll welding, hot pressing welding, ultrasonic welding, laser welding or resistance welding.

[0154] According to some embodiments of this application, "providing a base film" includes: connecting membrane I and membrane II; performing a heat-melting treatment on the connection between membrane I and membrane II; and connecting membrane I and membrane II after cooling to form a base film.

[0155] The temperature for the heat fusion treatment is selected based on the melting points of membrane materials I and II. When membrane material I is polyimide and membrane material II is polypropylene, the heat fusion treatment temperature can be between 200℃ and 400℃. The heat fusion treatment can form a continuous whole at the junction of membrane materials I and II, resulting in a high bonding strength at the junction and thus improving the overall stability of the base film.

[0156] According to some embodiments of this application, referring to FIG8, "setting tabs on the surface of the conductive layer corresponding to film II" includes: with conductive layers covering both sides of the base film, setting a first tab 2314-1 on one side of the conductive layer surface and setting a second tab 2314-2 on the other side of the conductive layer surface, conductively connecting the first tab 2314-1 and the second tab 2314-2, and welding the first tab 2314-1 / second tab 2314-2 to the conductive layer.

[0157] Taking Figure 8 as an example, a first tab 2314-1 is provided on the surface of the conductive layer on the left, and a second tab 2314-2 is provided on the surface of the conductive layer on the right. The first tab 2314-1 and the second tab 2314-2 are electrically connected by a transfer roller weld, and then the first tab 2314-1 is fixed to the conductive layer on the left by ultrasonic welding.

[0158] By setting the first tab 2314-1 and the second tab 2314-2, the conductive channels can be increased, thereby improving the current carrying capacity of the composite current collector 231 and reducing the overall resistance of the composite current collector 231. In addition, the tab structure can improve the reliability of the connection and reduce the risk of increased resistance and overheating caused by poor connection.

[0159] According to some embodiments of this application, and further referring to FIG8, the lengths of the first tab 2314-1 and the second tab 2314-2 are different.

[0160] Taking Figure 8 as an example, the length of the first electrode tab 2314-1 on the left side is longer than the length of the second electrode tab 2314-2 on the right side. The first electrode tab 2314-1 and the second electrode tab 2314-2 are set to have different lengths, that is, the electrode tab on one side is set to be a short electrode tab in order to reduce the total number of electrode tab layers and reduce the problem of cold solder joints during subsequent welding.

[0161] According to some embodiments of this application, this application also provides a composite current collector, which is prepared by any of the above-described preparation methods.

[0162] According to some embodiments of this application, this application provides an electrical device including any of the batteries described above.

[0163] Example

[0164] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0165] Example 1

[0166] [Composite current collector]

[0167] The composite current collector consists of a main body region and a tab region. The tensile strength of the main body region is 350 MPa, and the tensile strength of the tab region is 170 MPa.

[0168] Along the thickness direction, the composite current collector includes a base film, metal bonding layers disposed on both sides of the base film, a conductive layer disposed outside the metal bonding layers, and external tabs. The base film includes film I, film II, and film III, with film II and film III disposed on both sides of film I, corresponding to the main body region, and film II corresponding to the tab region. The film material of film I is polyimide, including biphenyl polyimide and pyromellitic polyimide, with biphenyl polyimide accounting for 70% of the total mass. The film materials of film II and film III are low molecular weight polypropylene. The thickness of film I, film II, and film III is 6 μm, and the width of film III is 2 mm. The metal bonding layer is a nickel layer with a thickness of 70 nm. The conductive layer is a copper layer with a thickness of 1 μm.

[0169] It should be noted that the tensile strength of both the main body area and the tab area was tested using a sample that was 4.5 μm thick, 15 mm wide, and 100 mm long. The test method was as follows: the sample was placed between the upper and lower clamps of the tensile testing machine with a clamping distance of 50 mm. After clamping, the tensile testing machine was started until it broke. The tensile rate was 50 mm / min, and the strength at the point of breakage was recorded as the tensile strength.

[0170] [Positive electrode plate]

[0171] The positive electrode sheet includes a positive current collector and a positive active material layer. The positive current collector is a 13μm thick aluminum foil; the positive active material layer includes the positive active material NCM 811, the binder polyvinylidene fluoride (PVDF), and the conductive agent superconducting carbon black (SP), with a mass ratio of NCM 811, PVDF, and superconducting carbon black of 96:1.5:2.5.

[0172] NCM 811, polyvinylidene fluoride, and superconducting carbon black were added to N-methylpyrrolidone (NMP) solvent in a mass ratio of 96:1.5:2.5. The mixture was stirred thoroughly under vacuum until the system was homogeneous, yielding a positive electrode slurry with a solid content of 70%. The positive electrode slurry was then uniformly coated onto both sides of an aluminum foil using a coating machine, achieving an areal density of 14.9 mg / cm³. 2 The positive electrode sheet is obtained by cold pressing, slitting, and die cutting.

[0173] [Negative electrode plate]

[0174] The negative electrode sheet includes a negative current collector and a negative active material layer. The negative current collector is a composite current collector, and the negative active material layer includes negative active materials graphite and silicon oxides, negative binder styrene-butadiene rubber, conductive agent superconducting carbon black, and thickener sodium carboxymethyl cellulose. The mass ratio of graphite, silicon oxides, styrene-butadiene rubber, superconducting carbon black, and sodium carboxymethyl cellulose is 80:15:3:0.8:1.2.

[0175] Graphite and silicon oxide compounds, styrene-butadiene rubber (anode binder), superconducting carbon black (conductive agent), and sodium carboxymethyl cellulose (thickener) were added to deionized water in a mass ratio of 80:15:3:0.8:1.2. The mixture was thoroughly stirred under vacuum until homogeneous, forming a cathode slurry with a solid content of 48%. The cathode slurry was then uniformly coated onto both sides of the composite current collector using a coating machine, achieving a surface density of 8.2 mg / cm³. 2 The negative electrode sheet is obtained by cold pressing, slitting, and die cutting.

[0176] [Isolation membrane]

[0177] The separator is a polyethylene film with a thickness of 12μm.

[0178] Electrolyte

[0179] The electrolyte is a 1 mol / L lithium hexafluorophosphate (LiPF6) solution, and the solvent system is EC:DMC:EMC (volume ratio) = 1:1:1.

[0180] The positive electrode, separator, and negative electrode are placed in sequence and wound to obtain a wound electrode assembly. The wound electrode assembly is then placed in an outer package, injected with electrolyte, and sealed to obtain a battery.

[0181] Example 2

[0182] Unlike Example 1, the tensile strength of the main body region in this example is 376 MNPa, while the rest is the same as in Example 1.

[0183] Example 3

[0184] Unlike Example 1, the tensile strength of the main body region in this example is 312 MPa, while the rest is the same as in Example 1.

[0185] Example 4

[0186] Unlike Example 1, in this example, the thickness of membrane I, membrane II and membrane III are all 7 μm, and the rest are the same as in Example 1.

[0187] Example 5

[0188] Unlike Example 1, in this example, the thickness of membrane I, membrane II and membrane III are all 4 μm, and the rest are the same as in Example 1.

[0189] Comparative Example 1

[0190] Unlike Example 1, the base film of this comparative example is an integral polypropylene film material with a tensile strength of [value missing], while the rest is the same as in Example 1.

[0191] Comparative Example 2

[0192] Unlike Example 1, the negative electrode current collector in this comparative example is copper foil, while the rest is the same as in Example 1.

[0193] Performance testing

[0194] Energy density: Weigh the battery and record its mass as m. Charge it to 4.2V at a constant rate of 0.33C at 25℃ and let it stand for 10 minutes. Then discharge it to 2.5V at a constant rate of 0.33C and let it stand for 10 minutes. Cycle the charge and discharge cycle for 3 times and record the energy W of the battery in the 3rd cycle. Divide the energy W by the battery mass m to get the energy density.

[0195] Welding pull force: After welding, use a tensile testing machine to clamp the adapter piece at one end and the bottom of the electrode at the other end. The electrode width is 40mm. Record the force after the weld is completely pulled apart at a speed of 50mm / min.

[0196] Full charge elongation: After winding, disassemble the electrode assembly stack and draw three lines (top, middle, and bottom) at 100mm intervals on the large surface of the negative electrode sheet (the straight part of the wound electrode assembly). There are a total of nine lines on the three large surfaces. Record the width of each line. After drawing the lines, rewind the battery. After full charge, disassemble the battery and remeasure the width of the lines. The percentage increase in width compared to before full charge is the elongation. Take the average of the elongation of the nine lines as the final full charge elongation.

[0197] Capacity retention after 1000 cycles: At 25°C, charge at a constant rate of 0.33C to 4.2V, then maintain the voltage at 0.05C, and let stand for 10 minutes; then discharge at a constant rate of 0.33C to 2.5V, let stand for 10 minutes, and record the discharge capacity C0; repeat the above steps until 1000 cycles are reached, and record the discharge capacity C. 1000 Battery capacity retention rate = C 1000 / C0*100%.

[0198] The parameter settings for Examples 1-5 and Comparative Examples 1-2 are shown in Table 1.

[0199] Test Results

[0200] The test results are shown in Table 1.

[0201] Table 1. Test results from Examples 1-5 and Comparative Examples 1-2

[0202] As shown in Table 1, the full-charge elongation of the negative electrode sheet in this application is lower than that in the comparative examples. In Example 2, the full-charge elongation of the negative electrode sheet is the lowest at 0.39%, a decrease of 72.1% compared to Comparative Example 1. This indicates that the use of a higher-strength film material in this application can significantly suppress the expansion and elongation of the negative electrode active material layer, thereby reducing the elongation of the negative electrode sheet. The reduced elongation of the negative electrode sheet helps improve the battery's capacity retention rate. Furthermore, compared to the copper foil in Comparative Example 2, the full-charge elongation of the negative electrode sheet in this application is also lower.

[0203] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A battery comprising electrodes, wherein, The electrode includes a composite current collector, which, along its thickness direction, includes a base film and a conductive layer formed on at least one surface of the base film. The composite current collector includes a main body region and a tab region, wherein the tensile strength of the main body region is greater than the tensile strength of the tab region.

2. The battery as claimed in claim 1, wherein, The tensile strength of the main body region is 300MPa-1000MPa; and / or, the tensile strength of the tab region is 100MPa-200MPa.

3. The battery as described in claim 1 or 2, wherein, The base membrane includes membrane I and membrane II connected together. Membrane I is disposed corresponding to the main body region, and membrane II is disposed corresponding to the tab region. The tensile strength of membrane I is greater than that of membrane II.

4. The battery as claimed in claim 3, wherein, The membrane II satisfies at least one of the following conditions: The melting point of the membrane material of membrane II is 100℃-200℃; The polymer backbone of the membrane material of membrane II is a carbon chain.

5. The battery as claimed in claim 4, wherein, The membrane material of membrane I includes at least one of polyimide, high molecular weight polypropylene, polyethylene terephthalate, and polyimide-polypropylene copolymer; and / or, The membrane material of membrane II includes at least one of polyethylene and low molecular weight polypropylene.

6. The battery as claimed in claim 5, wherein, The degree of polymerization n1 of polyimide and the degree of polymerization n2 of polypropylene in the polyimide-polypropylene copolymer satisfy n1:n2=(7-9):(1-3).

7. The battery as claimed in claim 5, wherein, The polyimide includes at least a biphenyl polyimide, wherein the biphenyl polyimide accounts for 70%-100% of the total mass of the polyimide.

8. The battery according to any one of claims 3 to 7, wherein, The thickness of membrane I is greater than or equal to the thickness of membrane II.

9. The battery as claimed in claim 8, wherein, The thickness difference between membrane I and membrane II is 0 μm-0.5 μm.

10. The battery as claimed in claim 9, wherein, The thickness of membrane I is 3μm-7μm.

11. The battery according to any one of claims 3 to 10, wherein, The base membrane also includes membrane III, which is disposed on both sides of membrane I, and membrane III is disposed corresponding to the main body area.

12. The battery of claim 11, wherein, The width of membrane III is 1mm-5mm.

13. The battery of claim 11, wherein, The membrane material of membrane III includes at least one of polyethylene and low molecular weight polypropylene.

14. The battery according to any one of claims 1 to 13, wherein, Along the thickness direction, the composite current collector also includes a metal bonding layer, which is disposed between the base film and the conductive layer.

15. The battery of claim 14, wherein, The thickness of the metal adhesive layer is 50nm-150nm.

16. The battery of claim 14, wherein, The metal adhesive layer includes at least one of nickel, iron, chromium, and cobalt.

17. The battery according to any one of claims 1 to 16, wherein, The thickness of the conductive layer is 0.5μm-1.5μm.

18. The battery of claim 17, wherein, The conductive layer includes at least one of aluminum, aluminum alloy, copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy.

19. The battery according to any one of claims 1 to 18, wherein, The tab area is provided with a soldering area, and the soldering area is 1mm-5mm away from the junction of the tab area and the main body area.

20. The battery of claim 19, wherein, The composite current collector also includes an external electrode tab, which is disposed in the solder area of ​​the electrode tab region.

21. The battery according to any one of claims 1 to 20, wherein, Along the thickness direction, the electrode also includes an active material layer, which is disposed on at least one side surface of the composite current collector and covers the junction between the main body region and the tab region.

22. A method for preparing a composite current collector, wherein, include: A base membrane is provided, the base membrane comprising membrane I and membrane II connected together, wherein the tensile strength of membrane I is greater than the tensile strength of membrane II; A conductive layer is coated on at least one surface of the base film; A tab is provided on the surface of the conductive layer at a position corresponding to the film II.

23. The method for preparing the composite current collector as described in claim 22, wherein, The "providing of a base film" includes: Connect membrane I and membrane II; The junction of membrane I and membrane II is subjected to heat fusion treatment, and after cooling, membrane I and membrane II are joined to form the base membrane.

24. The method for preparing the composite current collector as described in claim 22 or 23, wherein, The phrase "providing tabs on the surface of the conductive layer at a location corresponding to film II" includes: With conductive layers covering both sides of the base film, a first tab is provided on one side of the conductive layer surface, and a second tab is provided on the other side of the conductive layer surface. The first tab and the second tab are electrically connected, and the first tab / second tab is welded to the conductive layer.

25. The method for preparing the composite current collector as described in claim 24, wherein, The first and second electrodes are of different lengths.

26. A composite current collector, prepared by the preparation method according to any one of claims 22 to 25.

27. An electrical appliance, wherein, Includes the battery as described in any one of claims 1 to 21.

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