Secondary battery, preparation method thereof and electric device

Abstract

The invention discloses a secondary battery, a preparation method thereof and an electric device. The secondary battery comprises an electrode plate, the electrode plate comprises a porous metal foil, the porous metal foil comprises a first porous layer, a solid layer and a second porous layer, and the solid layer is laminated and combined between the first porous layer and the second porous layer; the first porous layer comprises a first surface layer and a first transition layer, and the porosity of the first surface layer is greater than that of the first transition layer; the second porous layer comprises a second surface layer and a second transition layer, and the porosity of the second surface layer is larger than that of the second transition layer. According to the three-dimensional porous metal foil, the solid layer is introduced between the two porous layers, so that the tensile property of the whole three-dimensional porous metal foil can be improved. And meanwhile, the porosity of the porous layer is changed in a gradient manner, so that the transition between the porous layer and the solid layer is stable and relaxed, the stress distribution of the porous metal foil with the three-layer structure is more uniform, and the interlayer peeling strength is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a secondary battery and its preparation method and electrical device. Background Technology

[0002] Current collectors are important components of the positive and negative electrodes in lithium-ion battery cells. As a structure or component that collects current, their main function is to gather the current generated by the battery's active materials to form a larger current for output, thereby completing the conversion of chemical energy into electrical energy. In lithium-ion batteries, current collectors mainly refer to metal foils, such as copper foil and aluminum foil.

[0003] Currently, lithium battery manufacturing primarily relies on winding. The winding process requires the current collector to possess a certain degree of flexibility and ductility. Porous copper foil can be used as a current collector in lithium batteries to uniformly distribute current density while suppressing lithium dendrite formation. However, while porous foil offers increased flexibility compared to conventional foil, it reduces the tensile strength of the electrode, making it difficult to wind in the process. Summary of the Invention

[0004] In view of the above problems, this application provides a method for preparing a secondary battery and an electrical device thereof, which aims to solve the problem of poor mechanical properties of porous metal foil.

[0005] In a first aspect, embodiments of this application provide a secondary battery, including an electrode sheet comprising a porous metal foil, the porous metal foil comprising a first porous layer, a solid layer, and a second porous layer, the solid layer being stacked between the first porous layer and the second porous layer; the solid layer having a dense structure; the first porous layer comprising a first surface layer and a first transition layer, the first transition layer being distributed between the first surface layer and the solid layer, the porosity of the first surface layer being greater than the porosity of the first transition layer; the second porous layer comprising a second surface layer and a second transition layer, the second transition layer being distributed between the second surface layer and the solid layer, the porosity of the second surface layer being greater than the porosity of the second transition layer.

[0006] The porous metal foil of this application embodiment includes a three-layer structure, which is stacked in a manner of "first porous layer / solid layer / second porous layer". By introducing a solid layer between the two porous layers, the tensile properties of the entire three-dimensional porous metal foil can be improved. Simultaneously, a transition layer is distributed at the junction of the porous layer and the solid layer. The porosity of this transition layer is lower than that of the surface layer of the porous layer, resulting in a gradient change in the porosity of the porous layer. This makes the transition between the porous layer and the solid layer smooth and gradual, allowing for a more uniform stress distribution in the three-layer porous metal foil structure and improving the interlayer peel strength. The current collector using this porous metal foil exhibits better conductivity and mechanical strength, thereby providing the secondary battery with better cycle stability.

[0007] In some embodiments, the porosity of the first surface layer is 65-80%.

[0008] In some embodiments, the porosity of the second surface layer is 65-80%. By controlling the porosity of the first and second surface layers within the above range, the porous metal foil can have better mechanical properties, while increasing the specific surface area of ​​the porous metal foil and loading more active materials.

[0009] In some embodiments, the porosity of the first transition layer is 10-40%.

[0010] In some embodiments, the porosity of the second transition layer is 10-40%. By controlling the porosity of the first and second transition layers within the above range, the porous layer can have a more suitable porosity gradient, making the transition between the porous layer and the solid layer smoother and gentler, and improving the interlayer peel strength.

[0011] In some embodiments, the thickness of the first porous layer ranges from 50 to 200 μm.

[0012] In some embodiments, the thickness of the second porous layer ranges from 50 to 200 μm. By controlling the thicknesses of the first and second porous layers within the above range, the volume change during lithium insertion / extraction of the negative electrode active material can be better mitigated.

[0013] In some embodiments, the thickness of the first transition layer ranges from 5 to 30 μm.

[0014] In some embodiments, the thickness of the second transition layer ranges from 5 to 30 μm. By controlling the thicknesses of the first and second transition layers within the above range, the porous metal foil can have stronger interlayer peel strength.

[0015] In some embodiments, the thickness of the solid layer is 2–28 μm. By controlling the thickness of the solid layer within the above range, the tensile strength of the porous metal foil can be improved, and the porous metal foil can also have a suitable porosity.

[0016] In some embodiments, the material of the first porous layer includes at least one selected from elemental copper, manganese-copper alloy, copper-aluminum alloy, copper-zinc alloy, and copper-nickel alloy. The material of the solid layer includes elemental copper; the material of the second porous layer includes at least one selected from elemental copper, manganese-copper alloy, copper-aluminum alloy, copper-zinc alloy, and copper-nickel alloy. The porous metal foil can be a porous copper foil or a porous copper alloy foil containing other metallic elements, such as a porous manganese-copper alloy foil.

[0017] In some embodiments, the electrode sheet is a negative electrode sheet.

[0018] Secondly, embodiments of this application provide a method for preparing a secondary battery, comprising the following steps: preparing a porous metal foil; using the porous metal foil as a negative electrode current collector to prepare a negative electrode sheet; and assembling an electrode assembly to obtain a secondary battery; the step of preparing the porous metal foil includes the following:

[0019] A metal multilayer body is provided, the metal multilayer body comprising a first alloy layer, a single metal layer and a second alloy layer stacked sequentially.

[0020] The metal multilayer is subjected to a first annealing treatment, which forms a first diffusion layer at the interface between the first alloy layer and the metal elemental layer, and forms a second diffusion layer at the interface between the second alloy layer and the metal elemental layer; thus obtaining an alloy precursor.

[0021] The alloy precursor is subjected to phase separation heat treatment and dealloying treatment, and then subjected to a second annealing treatment, so that the first alloy layer forms the first surface layer, the first diffusion layer forms the first transition layer, the second alloy layer forms the second surface layer, and the second diffusion layer forms the second transition layer, thereby obtaining the porous metal foil.

[0022] The above preparation method involves subjecting a multilayer metal body to a first annealing treatment, which induces interlayer thermal diffusion between the alloy layers and the elemental metal layers. This allows alloying elements to diffuse away from the interlayer interfaces, gradually causing the interfaces to disappear and forming a diffusion layer. Then, selective etching is performed to remove the alloying elements from both the alloy and diffusion layers. The removed alloying elements form pores, and after further annealing, a three-layer porous metal foil with a solid layer is obtained.

[0023] In some embodiments, the thickness of the elemental metal layer in the rolled metal multilayer is 20–50 μm. By controlling the thickness of the intermediate elemental metal layer in the metal multilayer to be within the range of 20–50 μm, the operating space for subsequent heat treatment is increased, thereby improving the mechanical properties of the final porous metal foil.

[0024] In some embodiments, the temperature of the first annealing treatment is 750–850°C, and the time is 10–30 min. The purpose of the first annealing treatment is to cause elemental segregation in the rolled metal multilayer, to cause alloying elements to diffuse at the interface between the alloy layer and the metal elemental layer, and to cause the alloying elements to diffuse deeply into the metal elemental layer, thereby forming a diffusion layer at the interface, and partially or completely eliminating rolling orientation and stress.

[0025] In some embodiments, the conditions for the second annealing treatment include: a temperature of 700–900°C, a time of 20–60 min, and an annealing atmosphere comprising a mixture of hydrogen and argon. The second annealing treatment is carried out in a reducing atmosphere to reduce the oxides in the dealloyed metal foil, such as reducing copper oxide to copper, thereby stabilizing the crystal structure in the metal foil.

[0026] Thirdly, embodiments of this application provide an electrical device including the secondary battery described in the first aspect. By employing the secondary battery of this application, the operational stability of the electrical device is improved.

[0027] 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

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0029] Figure 1 This is a schematic diagram of the structure of the porous metal foil according to an embodiment of this application;

[0030] Figure 2 This is a cross-sectional electron microscope image (800x) of the porous metal foil of Embodiment 1 of this application;

[0031] Figure 3 This is a cross-sectional electron microscope image (2000x) of the porous metal foil of Embodiment 1 of this application;

[0032] Figure 4 This is a cross-sectional electron microscope image (800x) of the porous metal foil of Embodiment 13 of this application;

[0033] Figure 5 This is a cross-sectional electron microscope image (2000x) of the porous metal foil of Embodiment 13 of this application;

[0034] Figure 6 This is a cross-sectional electron microscope image (800x) of the porous metal foil of Comparative Example 1 of this application;

[0035] Figure 7 This is a cross-sectional electron microscope image (2000x) of the porous metal foil of Comparative Example 1 of this application;

[0036] Figure 8This is an EDS line scan of the cross-section of the cold-rolled sheet corresponding to the porous metal foil of Embodiment 1 of this application;

[0037] Figure 9 This is an EDS line scan of the cross-section of the cold-rolled sheet material corresponding to the porous metal foil in Embodiment 1 of this application after crystallization annealing.

[0038] Figure 10 EDS line scan images of the cross-section of the cold-rolled sheet material corresponding to the porous metal foil of Embodiment 1 of this application after crystallization annealing and phase separation heat treatment;

[0039] Figure 11 EDS line scan images of the cross sections of the cold-rolled sheet corresponding to the porous metal foil of Embodiment 1 of this application after crystallization annealing, phase separation heat treatment, dealloying and reduction annealing; Note: Mn(at%) represents the EDS line scan curve (at%) of Mn, Cu(at%) represents the EDS line scan curve (at%) of Cu.

[0040] Figure 12 This is a schematic diagram of the structure of a secondary battery according to some embodiments of this application;

[0041] Figure 13 This is a schematic diagram of the structure of a battery cell according to some embodiments of this application;

[0042] Figure 14 This is a schematic diagram of a battery module according to some embodiments of this application;

[0043] Figure 15 This is a schematic diagram of a battery pack according to some embodiments of this application;

[0044] Figure 16 for Figure 15 An exploded view of a battery pack according to some embodiments of this application is shown;

[0045] Figure 17 This is a schematic diagram of the structure of the electrode assembly in some embodiments of this application;

[0046] Figure 18 This is a schematic diagram of the structure of an electrical device according to some embodiments of this application.

[0047] The reference numerals in the detailed embodiments are as follows:

[0048] 01-Housing; 02-Cover plate; 03-Electrode assembly; 04-Battery cell; 05-Battery module; 06-Upper casing; 07-Lower casing;

[0049] 101 - Negative electrode plate; 102 - Positive electrode plate; 201 - Negative electrode tab; 202 - Positive electrode tab; 203 - Diaphragm;

[0050] 40 - Secondary battery; 50 - Electrical device; 501 - Controller; 502 - Motor;

[0051] 100 - First porous layer; 110 - First surface layer; 120 - First transition layer; 200 - Solid layer; 300 - Second porous layer; 310 - Second surface layer; 320 - Second transition layer. Detailed Implementation

[0052] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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).

[0058] In the description of the embodiments of this application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0059] In the description of the embodiments of this application, unless otherwise expressly specified and limited, the technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0060] The tensile strength of porous metals is inversely proportional to their porosity; that is, the higher the porosity, the lower the tensile strength. Furthermore, intergranular corrosion in metals disrupts the bonding between grains, significantly reducing the metal's mechanical strength. Due to the combined effects of intergranular corrosion and stress accumulation, porous structures often suffer from low tensile strength and poor interlaminar peel strength.

[0061] Based on this, embodiments of this application provide a secondary battery, which includes electrode sheets, the electrode sheets comprising porous metal foil, such as... Figure 1 As shown, the porous metal foil includes a first porous layer 100, a solid layer 200, and a second porous layer 300, with the solid layer 200 stacked between the first porous layer 100 and the second porous layer 300; the solid layer 200 has a dense structure; the first porous layer 100 includes a first surface layer 110 and a first transition layer 120, with the first transition layer 120 distributed between the first surface layer 110 and the solid layer 200, and the porosity of the first surface layer 110 being greater than the porosity of the first transition layer 120; the second porous layer 300 includes a second surface layer 310 and a second transition layer 320, with the second transition layer 320 distributed between the second surface layer 310 and the solid layer 200, and the porosity of the second surface layer 310 being greater than the porosity of the second transition layer 320.

[0062] The porous metal foil of this application embodiment includes a three-layer structure, which is combined in a stacked manner of "first porous layer / solid layer / second porous layer". The solid layer refers to a material with a dense internal structure, a compact texture, no obvious pores or cracks, and a relatively uniform stress distribution. By introducing a solid layer between two porous layers, the tensile properties of the entire three-dimensional porous metal foil can be improved. Simultaneously, the porous layer also includes a surface layer and a transition layer. That is, a transition layer is distributed on the side of the porous layer near the solid layer. The porosity of the transition layer is lower than that of the surface layer, which causes the porous layer to exhibit a continuous or phased change. That is, the porosity of the porous layer changes from high to low in a phased or continuous manner from the side away from the solid layer to the side adjacent to the solid layer. Because the porosity of the porous layer changes in a gradient, the transition between the porous layer and the solid layer is smooth and gradual, which can make the stress distribution of the three-layer porous metal foil more uniform and improve the interlayer peel strength. When porous metal foil is subjected to external forces such as winding, tension, and compression, the peel strength between the porous layer and the solid layer is higher, and the mechanical properties are better.

[0063] In some embodiments, the porosity of the first surface layer is 65-80%. As an example, the porosity of the first surface layer includes, but is not limited to, any one of 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, or a range of values ​​between any two.

[0064] In some embodiments, the porosity of the second surface layer is 65-80%. As an example, the porosity of the second surface layer includes, but is not limited to, any one of 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, and 80%, or a range between any two. If the surface porosity of the porous layer is too low (<65%), it cannot hold enough active material, failing to improve battery capacity; if the surface porosity is too high (>80%), the mechanical properties of the porous foil will decrease. Controlling the porosity of the first and second surface layers within the above ranges allows the porous metal foil to have better mechanical properties while further increasing its specific surface area, thereby providing a larger reaction interface, loading more active material, and improving battery capacity and power.

[0065] In some embodiments, the porosity of the first transition layer is 10-40%. As an example, the porosity of the first transition layer can be any one of 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any range between two.

[0066] In some embodiments, the porosity of the second transition layer is 10-40%. As an example, the porosity of the second transition layer can be any one of 10%, 15%, 20%, 25%, 30%, 35%, or 40%, or a range between any two. Controlling the porosity of the transition layer within the above range allows for a more suitable porosity gradient in the porous layer, resulting in a smoother and gentler transition between the porous layer and the solid layer, further improving interlayer peel strength.

[0067] In some embodiments, the thickness of the first porous layer ranges from 50 to 200 μm. As an example, the thickness of the first porous layer includes, but is not limited to, any one of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, and 200 μm, or a range of values ​​between any two.

[0068] In some embodiments, the thickness of the second porous layer ranges from 50 to 200 μm. As an example, the thickness of the second porous layer includes, but is not limited to, any one of 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, and 200 μm, or a range between any two. Controlling the thickness of the first and second porous layers within the above range allows for the loading of more negative electrode active material. Furthermore, negative electrode active materials undergo structural expansion or contraction during charging and discharging due to lithium insertion / extraction. Taking silicon-based negative electrode materials as an example, the lithium insertion / extraction process causes strong crystal reconstruction and phase transitions, resulting in significant volume changes and consequently degrading electrode material performance. When the porous layer has a thickness within the above range, the volume changes during lithium insertion / extraction of the negative electrode active material can be better mitigated.

[0069] In some embodiments, the thickness of the first transition layer ranges from 5 to 30 μm. As an example, the thickness of the first transition layer includes, but is not limited to, any one of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm, or any range between two of them.

[0070] In some embodiments, the thickness of the second transition layer ranges from 5 to 30 μm. The thickness of the second transition layer includes, but is not limited to, any one of 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm, or any value between two of these. If the thickness of the transition layer is too large, the porosity of the porous layer will decrease, and the thickness of the solid layer will also be too small, thus affecting the mechanical strength of the porous metal foil and the size of the reaction interface. If the thickness of the transition layer is too small, it will not improve the interfacial peel strength. Therefore, controlling the thickness of the first and second transition layers within the above ranges can both improve the interfacial peel strength of the porous metal foil and ensure that the porous metal foil has a suitable porosity.

[0071] In some embodiments, the thickness of the solid layer is 2–28 μm. As an example, in the porous metal foil of this application embodiment, the thickness of the solid layer includes, but is not limited to, any one of the following values ​​or a range between any two: 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, and 28 μm. A solid layer thickness greater than 28 μm will reduce the overall porosity of the porous metal foil, thereby reducing the reaction interface of the porous metal foil. A solid layer thickness less than 2 μm will not enhance the mechanical properties of the porous layer. Therefore, setting the solid layer within a suitable range can both improve the tensile strength of porous metal foil and give it a suitable porosity.

[0072] In some embodiments, the material of the first porous layer includes at least one of elemental copper, manganese-copper alloy, copper-aluminum alloy, copper-zinc alloy, and copper-nickel alloy.

[0073] In some embodiments, the solid layer is made of elemental copper.

[0074] In some embodiments, the material of the second porous layer includes at least one of elemental copper, manganese-copper alloy, copper-aluminum alloy, copper-zinc alloy, and copper-nickel alloy. For example, the porous metal foil can be a porous copper foil or a porous copper alloy foil containing other metallic elements, such as a porous manganese-copper alloy foil.

[0075] In some embodiments, the electrode is a negative electrode.

[0076] Secondly, embodiments of this application provide a method for preparing a secondary battery, comprising the following steps: preparing a porous metal foil; using the porous metal foil as a negative electrode current collector to prepare a negative electrode sheet; and assembling an electrode assembly to obtain a secondary battery; the step of preparing the porous metal foil includes the following:

[0077] S1: Provide a metal multilayer body, which includes a first alloy layer, a single metal layer and a second alloy layer stacked sequentially.

[0078] S2: The metal multilayer body is subjected to a first annealing treatment; a first diffusion layer is formed at the interface between the first alloy layer and the metal element layer, and a second diffusion layer is formed at the interface between the second alloy layer and the metal element layer; thus, an alloy precursor is obtained.

[0079] S3: The alloy precursor is subjected to phase separation heat treatment and dealloying treatment, and then subjected to a second annealing treatment, so that the first alloy layer forms the first surface layer, the first diffusion layer forms the first transition layer, the second alloy layer forms the second surface layer, and the second diffusion layer forms the second transition layer, to obtain a porous metal foil.

[0080] The preparation method in this embodiment first involves deep bonding of the alloy plate and the pure metal plate in the metal multilayer through a first annealing treatment. During this process, deep interdiffusion occurs between the alloy plate and the pure metal plate, that is, interatomic diffusion occurs at the interface between the alloy plate and the pure metal plate. Metal atoms on both sides of the interface diffuse across the interface to the other side to form a diffusion layer. Through interatomic diffusion, a strong bonding layer is formed, thus forming a plate with atomic-level bonding. The alloying elements change from high to low levels in stages or continuously from the surface of the alloy layer to the side closer to the metal element layer. Then, a phase separation heat treatment is performed to precipitate the α phase in the metal multilayer, which facilitates the dealloying process to obtain porous copper with structural self-supporting capabilities. Then, the dealloying process selectively etches away the alloying elements. The removed alloying elements form pores, and after annealing, a three-layer porous metal foil with a solid reinforcing layer is obtained.

[0081] The following is a detailed explanation of each step in preparing porous metal foil.

[0082] Step S1: Provide a metal multilayer body, which includes a first alloy layer, a single metal layer, and a second alloy layer stacked sequentially.

[0083] In some embodiments, the method for preparing a metal multilayer includes the following steps: grinding and polishing an alloy plate and a pure metal plate respectively, then bonding the ground and polished surfaces together, stacking them in the order of "alloy plate / pure metal plate / alloy plate", and then performing vacuum electron beam sealing welding to obtain a metal multilayer.

[0084] In some embodiments, the power density of vacuum electron beam sealing welding is 1000–1500 kW / cm². 2 Vacuum degree < 5 Pa.

[0085] In some embodiments, the alloy plate is selected from at least one of manganese-copper alloy plate, copper-aluminum alloy plate, copper-zinc alloy plate, and copper-nickel alloy plate. As an example, the preparation method of the manganese-copper alloy plate includes the following steps: preparing pure copper (purity requirement > 99.5%) and pure manganese (purity requirement > 99.5%) in a certain proportion, and preparing a manganese-copper binary alloy using a vacuum induction melting method. The alloy is then cut to a certain size and subjected to grinding, polishing, and cleaning.

[0086] In some embodiments, the process conditions for vacuum induction melting are: melting at 1000–1200°C for 1–5 hours under an argon atmosphere.

[0087] In some embodiments, grinding and polishing are performed until the roughness Ra value reaches the micrometer level (1 to 100 μm).

[0088] In some embodiments, the atomic percentage of manganese atoms in the manganese-copper alloy is 70-85%, and the atomic percentage of copper atoms is 15-30%. As an example, the atomic percentage of manganese atoms in the manganese-copper alloy includes, but is not limited to, any one of 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, and 85%, or a range between any two. As an example, the atomic percentage of copper atoms in the manganese-copper alloy includes, but is not limited to, any one of 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, and 30%, or a range between any two. By controlling the atomic percentages of manganese and copper atoms in the manganese-copper alloy within the above ranges, a porous metal foil with a more suitable porosity is obtained.

[0089] In some embodiments, the thickness ratio of the first alloy layer, the elemental metal layer, and the second alloy layer in the metal multilayer is (2-8):1:(2-8). As an example, the thickness ratio of the first alloy layer, the elemental metal layer, and the second alloy layer includes, but is not limited to, any one of 2:1:2, 2:1:8, 3:1:3, 4:1:4, 5:1:5, 6:1:6, 7:1:7, 8:1:8, and 8:1:2, or any range between two of these values. Controlling the thickness ratio of the first alloy layer, the elemental metal layer, and the second alloy layer within the above range allows the fabricated porous metal foil to possess both superior mechanical properties and high porosity.

[0090] In some embodiments, the metal multilayer body is further subjected to a hot rolling process during its preparation. The hot rolling process specifically involves heating and holding the metal multilayer body in an inert gas environment, and then hot rolling it to reduce the material thickness to below 6 mm.

[0091] In some embodiments, the hot rolling temperature is 780–820°C, and the holding time is 0.5–1 hour; the thickness of the hot-rolled sheet is in the range of 3–6 mm. As an example, the hot rolling temperature includes, but is not limited to, any one of 780°C, 790°C, 800°C, 810°C, and 820°C, or a range between any two. The holding time is determined according to specific production needs, including but not limited to, any one of 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, and 1 hour, or a range between any two. The hot rolling process combines alloy plates and elemental metal plates in a multilayer metal structure to form a hot-rolled sheet with atomic-level bonding.

[0092] In a specific embodiment, the hot rolling step of the metal multilayer body in step S1 is as follows: the metal multilayer body is heated at 800°C in an inert gas environment and held at that temperature for 1 hour, and then immediately hot rolled to roll the material thickness to 5 mm to obtain a hot-rolled sheet.

[0093] In some embodiments, the preparation process of the metal multilayer also includes a cold rolling process, the specific steps of which include: thinning the metal multilayer by cold rolling in multiple passes. The cold rolling process can be performed after the hot rolling process.

[0094] In some embodiments, the cold rolling tonnage can be 1000T (tons), and the single-pass reduction rate can be 25-35%. As an example, the single-pass reduction rate of cold rolling includes, but is not limited to, any one of 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, and 35%, or a range between any two. The reduction rate of cold rolling affects the surface roughness and tensile properties of the cold-rolled sheet. A higher reduction rate results in a lower surface roughness of the cold-rolled sheet, but if the reduction rate is too high (>35%), it will negatively impact the tensile properties of the material. Controlling the single-pass reduction rate of cold rolling within the above range allows for the production of cold-rolled sheets with low surface roughness and good tensile properties.

[0095] In some embodiments, the thickness of the elemental metal layer in the metal multilayer is 20–50 μm. The purpose of controlling the thickness of the elemental metal layer in the metal multilayer within the range of 20–50 μm is to increase the operating space for subsequent heat treatment and improve the mechanical properties of the final porous metal foil. If the thickness of the elemental metal layer is too low (<20 μm), it cannot provide sufficient space for thermal diffusion, leading to severe Mn diffusion in the intermediate layer (elemental metal layer) of the metal multilayer. This results in a fully diffused manganese-copper alloy in the intermediate layer, and therefore, after dealloying and annealing, a porous metal foil structure with a solid reinforcing layer cannot be obtained, resulting in poor mechanical properties. When the thickness of the intermediate layer (elemental metal layer) of the metal multilayer is high (>50 μm), it is equivalent to a high overall copper content in the metal multilayer. Although the mechanical properties are better, some porosity is sacrificed.

[0096] Step S2: The metal multilayer body from step S1 is subjected to a first annealing treatment to form a first diffusion layer at the interface between the first alloy layer and the metal elemental layer, and to form a second diffusion layer at the interface between the second alloy layer and the metal elemental layer; thus obtaining the alloy precursor.

[0097] In some embodiments, the temperature of the first annealing treatment is 750–850°C, the annealing time is 10–30 min, and water cooling is used. As an example, the temperature of the first annealing treatment includes, but is not limited to, 750°C.

[0098] The temperature range is any one of 760℃, 770℃, 780℃, 790℃, 800℃, 810℃, 820℃, 830℃, 840℃, and 850℃, or a range between any two. The first annealing treatment in this application is recrystallization annealing. The purpose of recrystallization annealing is to cause elemental segregation in the cold-rolled strip, resulting in a gradient distribution of alloying elements on both sides of the intermediate layer (metallic single layer), thereby partially or completely eliminating rolling orientation and stress. For recrystallization annealing of three-layer metal multilayers, it can also induce interlayer thermal diffusion, enhancing interlayer bonding. The more complete the thermal diffusion, the stronger the interlayer atomic interaction, and the greater the interlayer bonding force.

[0099] It is important to note that for three-layer metal multilayers, the first annealing treatment (recrystallization annealing) significantly affects the element diffusion between the metal elemental layers and the alloy layers. If element diffusion is too abundant, i.e., the heat treatment temperature is too high or the time is too long, the pure metal layer in the middle of the metal multilayer will become too thin or completely convert into an alloy layer. After dealloying and reduction annealing, this part of the alloy layer will become the middle layer of the porous metal foil, and obviously its effect on strengthening tensile strength is not as good as that of a solid reinforcing layer. At the same time, if the heat treatment temperature is too low or the time is too short, the element diffusion is insufficient, resulting in weak interlayer bonding. This weakness is carried over to subsequent phase separation heat treatment, dealloying, and reduction annealing steps, resulting in low interlayer peel strength of the final three-layer porous copper structure. By balancing the heat treatment parameters of the first annealing treatment (recrystallization annealing) with the thickness of the metal elemental layer of the metal multilayer, i.e., the thickness of the middle copper layer, a solid reinforcing layer of appropriate thickness can be retained for the three-layer porous copper foil, while maintaining sufficient interlayer bonding strength, ultimately improving the peel strength of the porous metal foil prepared by dealloying.

[0100] Step S3: Perform phase separation heat treatment and dealloying treatment on the alloy precursor, and then perform a second annealing treatment to form a first surface layer from the first alloy layer, a first transition layer from the first diffusion layer, a second surface layer from the second alloy layer, and a second transition layer from the second diffusion layer, thereby obtaining a porous metal foil.

[0101] In some embodiments, the phase separation heat treatment temperature is 620–680°C, and the time is 60–240 min. As an example, the phase separation heat treatment temperature includes, but is not limited to, any one of 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, and 680°C, or a range between any two. The purpose of the phase separation heat treatment in this embodiment is to precipitate the α phase, facilitating the obtaining of porous copper with self-supporting structural capabilities after dealloying.

[0102] In some embodiments, the dealloying process can be a chemical dealloying method. The steps of the chemical dealloying method include: placing the alloy precursor in hydrochloric acid with a concentration of 0.5 to 3 mol / L at a temperature of 60 to 80°C until no obvious bubbles are generated, selectively corroding away the alloying elements, and completing the dealloying process. For example, if the alloy layer is a manganese-copper alloy, then the Mn element is selectively corroded away.

[0103] In other embodiments, the dealloying process can be an electrochemical dealloying method. The specific method can be referred to the electrochemical dealloying method commonly used in the art, and will not be described in detail here.

[0104] In some embodiments, the second annealing treatment is a reduction annealing treatment. The conditions for the reduction annealing treatment include: a temperature of 700–900°C, a time of 20–60 min, and an annealing atmosphere comprising a mixture of hydrogen and argon, with a volume ratio of hydrogen to argon of (5–15):(85–95). Reduction annealing can reduce copper oxide in porous metal foil, stabilize the crystal structure of copper, promote the diffusion of copper atoms, make the distribution of copper atoms more uniform, and improve the flexibility of porous copper foil.

[0105] The following is a detailed description of the secondary battery and its components.

[0106] Figure 12 This is a schematic diagram of the structure of a secondary battery in some embodiments of this application. Depending on the packaging form, secondary batteries can be divided into battery cells, battery modules, and battery packs. Integrating one or more battery cells forms a battery module, which can provide higher voltage and capacity, and has specific output functions. Installing one or more battery modules in a battery casing, often along with a battery management system, forms a battery pack. This battery pack is typically a product provided to the user. Alternatively, one or more battery cells can be directly installed in a casing to form a battery pack.

[0107] Figure 13 This is a schematic diagram of a battery cell 04 in some embodiments of this application. The battery cell 04 is the most basic unit constituting a secondary battery. For example... Figure 13 As shown, the battery cell 10 includes a housing 01, an end cap 02, an electrode assembly 03, and other functional components. The electrode assembly typically includes a positive electrode, a negative electrode, and a separator. The positive and negative electrodes are alternately stacked, with a separator placed between them for isolation, resulting in a bare cell. Alternatively, the bare cell can be obtained by winding. The bare cell is placed in an outer packaging, injected with electrolyte, and then sealed to obtain the battery cell.

[0108] refer to Figure 14 This is an example battery module. In the battery module, multiple battery cells 30 can be arranged sequentially along the length of the battery module. Of course, they can also be arranged in any other arbitrary manner. Furthermore, these multiple battery cells 04 can be secured using fasteners.

[0109] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells 04 are received.

[0110] refer to Figure 15 and Figure 16This is an example of a battery pack. The battery pack may include a battery compartment and multiple battery modules 05 disposed within the battery compartment. The battery compartment includes an upper housing 06 and a lower housing 07, with the upper housing 06 covering the lower housing 07 to form a closed space for accommodating the battery modules 05. The multiple battery modules 05 can be arranged in any manner within the battery compartment.

[0111] Please refer to Figure 17 , Figure 17 This is a schematic diagram of the structure of electrode assembly 03 in some embodiments of this application. Electrode assembly 03 is the component in battery cell 04 where electrochemical reactions occur. Electrode assembly 03 is mainly formed by winding or stacking an electrode structure integrating negative electrode 101 and positive electrode 102, and a separator 203 is usually provided between adjacent negative electrode 101 and positive electrode 102.

[0112] The negative electrode 101 includes a negative current collector and a negative electrode material layer, the negative electrode material layer being deposited inside the negative current collector. As an example, the material of the negative current collector can be copper, gold, silver, etc., and the negative electrode material layer includes a negative electrode material, which can be lithium metal, silicon, silicon oxide, silicon alloy, etc.

[0113] In some embodiments, the secondary battery of this application is a lithium metal battery, in which case its negative electrode material includes, but is not limited to, elemental lithium metal. As an example, the negative electrode material can be lithium metal, or an alloy of lithium metal with other various metals or non-metals.

[0114] In some embodiments, the secondary battery of this application is a lithium metal battery without a negative electrode. In this case, its negative electrode consists only of a metal foil current collector. During the cycle, only the lithium in the positive electrode is used, and lithium metal is deposited and stripped off on the negative electrode side.

[0115] The positive electrode 102 includes a positive current collector and a positive electrode material layer, with the positive electrode material layer coated on the surface of the positive current collector. Taking a lithium-ion battery as an example, the material of the positive current collector can be aluminum, and the positive electrode material layer includes the positive electrode material, which can be lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide, etc.

[0116] The separator 203 is a porous plastic film that allows lithium ions in the electrolyte to pass through freely, but isolates the negative electrode 101 and the positive electrode 102, preventing electrons inside the battery from passing through freely. The separator 203 can be made of materials such as PP (polypropylene) or PE (polyethylene).

[0117] Both the negative and positive current collectors have portions without an active material layer, and these portions without an active material layer are provided with connecting tabs. Specifically, the negative current collector is connected to a negative tab 201, and the positive current collector is connected to a positive tab 202. During the charging and discharging process of the battery, the positive and negative electrode material layers react with the electrolyte. Tab 201 connects to the negative electrode adapter 303, and the positive electrode tab 202 connects to the positive electrode adapter 304 to form a current loop. Of course, in some embodiments, the portions of the negative and positive current collectors without an active material layer each constitute tabs.

[0118] Thirdly, embodiments of this application provide an electrical device including the secondary battery described in the first aspect. Because this electrical device uses the aforementioned secondary battery, its operational stability is improved.

[0119] The batteries disclosed in some embodiments of this application can be used, but are not limited to, in electrical devices such as vehicles, ships, or aircraft. A power system incorporating the batteries disclosed in this application can be used to construct such an electrical device.

[0120] For ease of explanation, the following embodiments will be described using a vehicle 50 as an example of an electrical device according to an embodiment of this application.

[0121] Please refer to Figure 18 , Figure 18 This is a schematic diagram of the structure of a vehicle 50 provided in some embodiments of this application. A secondary battery 40 is disposed inside the vehicle 50, and the secondary battery 40 may be located at the bottom, front, or rear of the vehicle 50. The secondary battery 40 can be used to power the vehicle 50; for example, the secondary battery 40 can serve as the operating power source for the vehicle 50. The vehicle 50 may also include a controller 501 and a motor 502. The controller 501 is used to control the secondary battery 40 to supply power to the motor 502, for example, to meet the power needs of the vehicle 50 during starting, navigation, and driving.

[0122] In some embodiments of this application, the secondary battery 40 can not only serve as the operating power source for the vehicle 50, but also as the driving power source for the vehicle 50, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 50.

[0123] The following description is based on specific embodiments.

[0124] 1. Examples of porous metal foil

[0125] Example A1

[0126] This application provides a porous metal foil and a method for preparing the same. The porous metal foil comprises a three-layer structure stacked in a manner consisting of a first porous layer, a solid layer, and a second porous layer. The first porous layer is made of a manganese-copper alloy, the solid layer is made of copper, and the second porous layer is made of a manganese-copper alloy.

[0127] In the first porous copper layer, the porosity of the first surface layer is 72%, and the porosity of the first transition layer is 24%. In the second porous copper layer, the porosity of the second surface layer is 73%, and the porosity of the second transition layer is 25%.

[0128] The average thickness of the first porous copper layer is 126 μm, and the average thickness of the first transition layer is 14 μm. The average thickness of the second porous copper layer is 120 μm, and the average thickness of the second transition layer is 15 μm. The average thickness of the solid layer is 7 μm.

[0129] This application provides a porous metal foil, the preparation method of which includes the following steps:

[0130] S1: Copper metal (purity > 99.5%) and manganese metal (purity > 99.5%) are provided, and a manganese-copper alloy ingot is prepared by vacuum induction melting. In this embodiment, the composition of the manganese-copper alloy ingot is Mn. 75 Cu 25 (Subscripts 75 and 25 represent the atomic percentages of Mn and Cu, respectively). Two manganese-copper alloy plates of the same thickness (30 mm) and one copper plate (6 mm) are stacked and bonded together in the order of "manganese-copper alloy plate / copper plate / manganese-copper alloy plate," and vacuum electron beam sealing is used for welding at a power density of 1200 kW / cm². 2 The vacuum degree is <5Pa, and the splicing is completed.

[0131] S2: The ingot obtained in step S1 is heated to 800°C in an argon atmosphere and held for 1 hour. Then, it is hot rolled to reduce the material thickness to less than 6 mm.

[0132] S3: The hot-rolled sheet is subjected to multiple cold rolling thinning passes with a tonnage of 1000T and a single reduction rate of about 30%, resulting in a multilayer metal with a copper layer (intermediate layer) thickness of about 21μm, a first alloy layer thickness of about 138μm, and a second alloy layer thickness of about 140μm.

[0133] S4: The metal multilayer body is subjected to a first annealing treatment (recrystallization annealing treatment) at a temperature of 800℃ for 20 minutes, and then cooled with water to obtain the alloy precursor.

[0134] S5: The alloy precursor is then subjected to phase separation heat treatment at 650℃ for 150 min, followed by free etching in a 1 mol / L hydrochloric acid solution at 70℃ to selectively etch away Mn until no bubbles are generated. The dealloyed alloy precursor is then subjected to a second annealing treatment at 800℃ for 40 min in a hydrogen-argon mixed atmosphere (hydrogen to argon volume ratio of 10:90) at 800 sccm. It is then furnace cooled to obtain a porous metal foil.

[0135] Example A2

[0136] The main difference between Example A2 and Example A1 is that: in the first porous copper layer, the porosity of the first surface layer is 66%, and the porosity of the first transition layer is 13%. In the second porous copper layer, the porosity of the second surface layer is 67%, and the porosity of the second transition layer is 12%.

[0137] The main difference between the preparation methods of Example A2 and Example A1 is that the manganese-copper alloy ingots used in the first and second alloy layers of the metal multilayer are composed of Mn. 70 Cu 30 (The subscripts 70 and 30 represent the atomic percentages of Mn and Cu, respectively).

[0138] Example A3

[0139] The main difference between Example A3 and Example A1 is that: in the first porous copper layer, the porosity of the first surface layer is 78%, and the porosity of the first transition layer is 38%. In the second porous copper layer, the porosity of the second surface layer is 77%, and the porosity of the second transition layer is 39%.

[0140] The main difference between the preparation methods of Example A3 and Example A1 is that the manganese-copper alloy ingots used in the first and second alloy layers of the metal multilayer are composed of Mn. 80 Cu 20 (The subscripts 80 and 20 represent the atomic percentages of Mn and Cu, respectively).

[0141] Example A4

[0142] The main difference between Example A4 and Example A1 is that the average thickness of the first porous copper layer is 61 μm and the average thickness of the second porous copper layer is 63 μm.

[0143] The main difference between the preparation methods of Example A4 and Example A1 is that in the metal multilayer, the thickness of the first alloy layer is about 67 μm and the thickness of the second alloy layer is about 70 μm.

[0144] Example A5

[0145] The main difference between Example A5 and Example A1 is that the average thickness of the first porous copper layer is 178 μm and the average thickness of the second porous copper layer is 183 μm.

[0146] In the metal multilayer, the thickness of the first alloy layer is approximately 186 μm, and the thickness of the second alloy layer is approximately 190 μm.

[0147] Example A6

[0148] The main difference between Example A6 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 22 μm.

[0149] The main difference between the preparation methods of Example A6 and Example A1 is that the thickness of the intermediate layer (copper layer) of the metal multilayer is about 30 μm.

[0150] Example A7

[0151] The main difference between Example A7 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 25 μm.

[0152] The main difference between the preparation methods of Example A7 and Example A1 is that the thickness of the solid layer of the metal multilayer is about 46 μm.

[0153] Example A8

[0154] The main difference between Example A8 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 9 μm. The average thickness of the first transition layer is 9 μm, and the average thickness of the second transition layer is 7 μm.

[0155] The main difference between the preparation methods of Example A8 and Example A1 is that the first annealing treatment (recrystallization annealing treatment) time is 10 min.

[0156] Example A9

[0157] The main difference between Example A9 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 5 μm. The average thickness of the first transition layer is 24 μm, and the average thickness of the second transition layer is 22 μm.

[0158] The main difference between the preparation methods of Example A9 and Example A1 is that the first annealing treatment (recrystallization annealing treatment) time is 30 min.

[0159] Example A10

[0160] The main difference between Example A10 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 10 μm. The average thickness of the first transition layer is 10 μm, and the average thickness of the second transition layer is 9 μm.

[0161] The main difference between the preparation methods of Example A10 and Example A1 is that the temperature of the first annealing treatment (recrystallization annealing treatment) is 750°C.

[0162] Example A11

[0163] The main difference between Example A11 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 4 μm. The average thickness of the first transition layer is 22 μm, and the average thickness of the second transition layer is 23 μm.

[0164] The main difference between the preparation methods of Example A11 and Example A1 is that the temperature of the first annealing treatment (recrystallization annealing treatment) is 850°C.

[0165] Example A12

[0166] The main difference between Example A12 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 10 μm, the average thickness of the first transition layer is 7 μm, and the average thickness of the second transition layer is 6 μm.

[0167] The main difference between the preparation methods of Example A12 and Example A1 is that the first annealing treatment (recrystallization annealing treatment) time is 5 min.

[0168] Example A13

[0169] The main difference between Example A13 and Example A1 is that the average thickness of the solid layer of the porous metal foil is 2 μm. The average thickness of the first transition layer is 25 μm, and the average thickness of the second transition layer is 27 μm.

[0170] The main difference between the preparation methods of Example A13 and Example A1 is that the first annealing treatment (recrystallization annealing treatment) time is 40 min.

[0171] Comparative Example A1

[0172] The main difference between Comparative Example A1 and Example A1 is that the thickness of the intermediate layer (copper layer) of the metal multilayer is about 13 μm, and the thickness of the solid layer of the porous metal foil is 0 μm.

[0173] 2. Battery Example

[0174] Example B1 and Comparative Example B1

[0175] In this embodiment B1 and comparative example B1, the porous metal foil of embodiment A1 and comparative example A1, respectively, is used as the negative electrode current collector, and secondary batteries are assembled according to the following methods:

[0176] (1) The positive electrode active material LiFePO4, conductive agent and binder are stirred in N-methylpyrrolidone solvent system at a mass ratio of 97:2:1. After being mixed evenly, the mixture is coated on Al foil, dried and rolled to obtain the positive electrode sheet.

[0177] (2) Rinse the negative electrode current collector with alcohol and bake it under vacuum at low temperature (50℃) for 2-4 hours. It can then be used directly as a negative electrode sheet.

[0178] (3) A polyethylene film is used as a separator (coated with a ceramic layer and a polymer layer).

[0179] (4) In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the electrolyte is 1M LiFSI (solvent is ethylene glycol dimethyl ether).

[0180] (5) "Use one negative electrode (without active material coating) and two positive electrode (with active material coating on one side) to assemble the stacked battery in the order of "positive electrode / separator / negative electrode / separator / positive electrode".

[0181] Performance testing

[0182] To verify the progressiveness of the embodiments of this application, the samples of the embodiments and comparative examples were subjected to the following tests:

[0183] 1. Testing the porosity of porous metal foil.

[0184] First, a three-layer porous copper cross-section polished sample was prepared using plasma cutting. Then, the cross-sectional morphology of the sample was tested using a ZEISS Sigma 300 scanning electron microscope. In the high-magnification morphology image (x5000), electron microscope images of corresponding regions (such as the first porous layer and the first transition layer) were extracted. The images were processed using Avizo software to separate the fibrous regions and porous regions. The proportion of the porous region area to the area of ​​the extracted region was calculated, which is the porosity on the selected region plane, and thus characterizes the porosity of the bulk phase.

[0185] 2. Thickness test of porous metal foil.

[0186] First, a three-layer porous copper cross-section polished sample was prepared using plasma cutting. Then, the cross-sectional morphology of the sample was tested using a ZEISS Sigma 300 scanning electron microscope. The thickness of each layer was measured using the distance measurement tool built into the scanning electron microscope, and the average value of multiple measurements (≥3 times) was used to characterize the thickness level of each layer.

[0187] 3. Tensile strength test.

[0188] The testing equipment is a universal tensile testing machine. During the test, the sample is cut into strips of a certain width and length, and clamped between the upper and lower jaws of the tensile testing machine, ensuring that the clamping is tight and the sample is not skewed. Then, the load is set to 50N and the tensile test is started to obtain the maximum load F1 that the sample can withstand before it breaks, in N.

[0189] The formula for calculating tensile strength is: σ = F1 / S, where S is the original cross-sectional area of ​​the specimen, in mm. 2 .

[0190] 4. Test of normal peel force.

[0191] The testing equipment was a universal tensile testing machine. During testing, the sample was cut into strips of a certain width and length, and double-sided tape was used to adhere the sample to a horizontal stage, ensuring that 1 / 3 of the sample's long side was exposed. An iron roller was used to roll over the remaining 2 / 3 of the sample to ensure firm adhesion. During testing, the exposed 1 / 3 of the sample's long side was bent upwards at a 90° angle and fixed to the grippers, ensuring tight clamping and no sample skewing. The displacement was then set to 20 mm, the speed 2 mm / s, and the peeling test began, obtaining a curve segment showing stable sample load.

[0192] The formula for calculating the normal peel force is: f = F2 / W, where F2 is the average value of the curve segment where the sample load is stable, in N, and W is the width of the double-sided adhesive tape, in m.

[0193] 5. Cross-sectional morphology observation.

[0194] First, a polished sample with a three-layer porous copper cross-section was prepared using plasma cutting. Then, the cross-sectional morphology of the sample was tested using a ZEISS Sigma 300 scanning electron microscope.

[0195] 6. Battery cycle performance test.

[0196] 1) Let stand for 12 hours; 2) Charge with a constant current at a rate of 0.1C to a voltage of 3.65V; 3) Let stand for 5 minutes; 4) Discharge with a constant current at a rate of 0.2C to a voltage of 2.5V; 5) Let stand for 5 minutes; 6) Charge with a constant current at a rate of 0.2C to a voltage of 3.65V, then charge at 3.65V to 0.1C; 7) Let stand for 5 minutes; 8) Discharge with a constant current at a rate of 1C to a voltage of 2.5V; 9) Let stand for 5 minutes; 10) Repeat steps 6-9 for 10 cycles; 11) Charge with a constant current at a rate of 0.1C to a voltage of 3.65V; 12) Let stand for 5 minutes; 13) Discharge with a constant current at a rate of 0.2C to a voltage of 2.5V; 14) Let stand for 5 minutes; 15) Repeat steps 6-14 for 200 cycles. Cyclic performance data are shown in Table 3.

[0197] Table 1

[0198]

[0199]

[0200] Note: The data in parentheses in the average thickness data of the solid layer is the thickness range of the solid layer. For example, the average thickness data of the solid layer in Example A1 is filled in as 7 (4-11), which means that the average thickness of the solid layer is 7 μm and the thickness range of the solid layer is 4-11 μm.

[0201] Table 2

[0202] Group Tensile strength / Mpa Interlayer peel strength / N.m -1 ]]> Presence of cracks in cross section Example Al 15.7 22.4 No Example A2 19.3 20.9 No Example A3 13.8 25.1 No Example A4 17.5 21.3 No Example A5 16.2 23.5 No Example A6 36.8 21.7 No Example A7 46.9 19.5 No Example A8 18.4 16.3 No Example A9 10.2 20.0 No Example A10 20.3 14.5 No Example A11 12.6 21.9 No Example A12 22.3 11.7 Yes Example A13 8.1 Brittle Yes Comparative Example Al 7.2 Brittle Yes

[0203] Table 3

[0204] Cycles Example Bl Comparative Example Bl 1 77.1％ 75.6％ 20 60.5％ 48.9％ 30 53.2％ 38.8％ 40 47.2％ 30.9％ 50 41.4％ 24.5％ 60 36.7％ 19.6％

[0205] Test results show that Figure 2 The image shown is a cross-sectional electron microscope image of the porous metal foil in Example A1. When the thickness of the intermediate layer of the cold-rolled sheet is 21 μm, the intermediate solid layer of the three-layer porous copper structure can be appropriately retained through recrystallization heat treatment (800℃ / 20min / water cooling), phase separation heat treatment (650℃ / 150min / furnace cooling), and dealloying and reduction annealing, which can enhance the tensile strength (15.7MPa). Figure 4 The image shown is a cross-sectional electron microscope image of the porous metal foil in Example A13. When the recrystallization heat treatment was extended from 20 min to 40 min, the manganese in the precursor diffused excessively. Only a very thin area of ​​the intermediate layer was not diffused by manganese. As a result, after dealloying and reduction annealing, the solid layer in the middle of the three-layer porous copper structure became thinner, and in some places the solid layer could not be seen, resulting in a decrease in tensile strength (8.1 MPa). Figure 6 The image shows a cross-sectional electron microscope (SEM) image of the porous metal foil in Comparative Example A1. When the thickness of the intermediate layer in the multilayer metal structure decreased from 21 μm to 13 μm, under the same heat treatment and dealloying conditions, excessive diffusion of manganese in the precursor occurred, meaning that manganese fully diffused throughout the intermediate layer. Ultimately, the intermediate layer of the three-layer porous copper structure became completely porous. The disappearance of the solid intermediate layer in the three-layer porous copper structure, accompanied by the formation of cracks, may be related to stress accumulation in the intermediate layer.

[0206] Figure 8 - Figure 11 The image shows a cross-sectional EDS line scan of Example A1, corresponding to the cross-sectional element variations of a porous copper structure with a solid layer. For example... Figure 8 As shown, the middle layer of the metal multilayer is essentially pure copper, with a clear elemental gradient between it and the alloy layers on either side. Figure 9 As shown, after recrystallization annealing heat treatment, the thickness of the middle pure copper layer in the metal multilayer becomes thinner, and the interlayer element gradient becomes gentler, indicating that element diffusion has occurred; asFigure 10 As shown, after recrystallization heat treatment and phase separation heat treatment, the thickness of the intermediate pure copper layer in the metal multilayer further decreases or even disappears, the interlayer element gradient further slows down, and element diffusion is more complete; as Figure 11 As shown, after recrystallization heat treatment, phase separation heat treatment, dealloying and reduction annealing, the middle pure copper layer platform reappears in the metal multilayer, and the two sides also become copper layers. However, there is a certain amount of manganese residue between the layers, which indicates that a structure with copper as the main component was obtained through dealloying and reduction annealing.

[0207] Table 2 shows that the porous metal foils of Examples A1 to A11 have good tensile strength and interlayer peel strength, and no cracks are found at the interfaces. Although the porous metal foil of Example A12 has an intermediate layer (copper layer) thickness of approximately 21 μm and a solid layer thickness ranging from 9 to 12 μm, the first annealing treatment (recrystallization annealing) time is only 5 min, which is too short, resulting in insufficient element diffusion, weak interlayer bonding, and cracks in the cross-section of the final porous metal foil. The porous metal foil of Example A13 has an excessively long first annealing treatment (recrystallization annealing) time of 40 min, leading to an excessively thin pure copper layer in the intermediate layer of the metal multilayer or its complete conversion into a manganese-copper alloy layer. This results in low tensile strength, poor interlayer peel strength, and cracks in the final porous metal foil. The porous metal foil of Comparative Example A1 has poor mechanical properties because the thickness of the intermediate layer (copper layer) of its metal multilayer is only 13μm. After dealloying and annealing, it is impossible to obtain a porous metal foil structure with a solid layer.

[0208] The cycle performance data in Table 3 represent the performance of the porous metal foil of this application when applied to a battery without any lithium-loving surface treatment.

[0209] 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 secondary battery characterized by comprising: The electrode tab comprises a porous metal foil, the porous metal foil comprises a first porous layer, a solid layer, and a second porous layer, the solid layer is laminated and combined between the first porous layer and the second porous layer; the solid layer has a dense structure; The first porous layer comprises a first surface layer and a first transition layer, the first transition layer is distributed between the first surface layer and the solid layer, the porosity of the first surface layer is greater than the porosity of the first transition layer; The second porous layer comprises a second surface layer and a second transition layer, the second transition layer is distributed between the second surface layer and the solid layer, the porosity of the second surface layer is greater than the porosity of the second transition layer.

2. The secondary battery according to claim 1, characterized by The porosity of the first surface layer ranges from 65% to 80%, and / or the porosity of the second surface layer ranges from 65% to 80%.

3. The secondary battery according to claim 2, characterized by The porosity of the first transition layer ranges from 10% to 40%, and / or the porosity of the second transition layer ranges from 10% to 40%.

4. The secondary battery according to any one of claims 1 to 3, characterized by The thickness of the first porous layer ranges from 50 μm to 200 μm; and / or the thickness of the second porous layer ranges from 50 μm to 200 μm.

5. The secondary battery according to claim 4, characterized by The thickness of the first transition layer ranges from 5 μm to 30 μm; and / or the thickness of the second transition layer ranges from 5 μm to 30 μm.

6. The secondary battery according to any one of claims 1 to 5, wherein The thickness of the solid layer ranges from 2 μm to 28 μm.

7. The secondary battery according to any one of claims 1 to 6, characterized by The material of the first porous layer comprises at least one of copper element, manganese-copper alloy, copper-aluminum alloy, copper-zinc alloy, and copper-nickel alloy; The material of the solid layer comprises copper element; The material of the second porous layer comprises at least one of copper element, manganese-copper alloy, copper-aluminum alloy, copper-zinc alloy, and copper-nickel alloy.

8. The secondary battery according to any one of claims 1 to 7, characterized by The electrode tab is a negative electrode tab.

9. A method of producing the secondary battery according to any one of claims 1 to 8, characterized by, The method comprises the following steps: Preparation of a porous metal foil; preparation of a negative electrode tab by taking the porous metal foil as a negative electrode current collector, assembly of an electrode assembly, and preparation of a secondary battery; the step of preparing the porous metal foil comprises the following: Providing a metal multilayer body, the metal multilayer body comprises a first alloy layer, a metal element layer, and a second alloy layer which are sequentially laminated and combined; Subjecting the metal multilayer body to a first annealing treatment, so that a first diffusion layer is formed at the interface between the first alloy layer and the metal element layer, and a second diffusion layer is formed at the interface between the second alloy layer and the metal element layer; Obtaining an alloy precursor; Subjecting the alloy precursor to a phase separation heat treatment, a dealloying treatment, and then a second annealing treatment, so that the first alloy layer forms the first surface layer, the first diffusion layer forms the first transition layer, the second alloy layer forms the second surface layer, and the second diffusion layer forms the second transition layer, thereby obtaining the porous metal foil.

10. The preparation method of the secondary battery according to claim 9, wherein The thickness of the metal element layer in the metal multilayer body ranges from 20 μm to 50 μm.

11. The method of claim 9, wherein the method further comprises the step of: The temperature of the first annealing treatment ranges from 750 ℃ to 850 ℃, and the time ranges from 10 min to 30 min.

12. The method of producing a porous metal foil according to claim 9, wherein The second annealing treatment has a temperature of 700-900 DEG C, a time of 20-60 minutes, and an annealing atmosphere including a mixture of hydrogen and argon.

13. An electrical device, characterized by The secondary battery includes the secondary battery according to any one of claims 1 to 8.

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