Secondary battery and manufacturing method therefor, and electrical device

Abstract

Disclosed in the present application are a secondary battery and a manufacturing method therefor, and an electrical device. The secondary battery of the present application comprises an electrode sheet, the electrode sheet comprising a porous metal foil; the porous metal foil comprises a first porous layer, a solid layer and a second porous layer, the solid layer being stacked 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, the porosity of the first surface layer being greater than the porosity of the first transition layer; the second porous layer comprises a second surface layer and a second transition layer, the porosity of the second surface layer being greater than the porosity of the second transition layer. The present application introduces the solid layer between the two porous layers, so that the tensile properties of the whole three-dimensional porous metal foil can be improved. In addition, since the porous layers exhibit a gradient in porosity, the transition between the porous layers and the solid layer is smooth and mild, allowing the porous metal foil having a three-layer structure to exhibit more uniform stress distribution, thereby improving the interlayer peel strength.

Description

Secondary battery, preparation method thereof, and electric device

[0001] This application claims priority to the Chinese patent application No. 202410942961.8, filed on July 15, 2024 in the China Patent Office, and entitled "Secondary battery, preparation method thereof, and electric device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application belongs to the technical field of batteries, and in particular relates to a secondary battery, a preparation method thereof, and an electric device. BACKGROUND

[0003] The current collector is an important component of the positive and negative electrodes in a lithium battery cell. As a structure or part for collecting current, its main function is to collect the current generated by the battery active material to form a larger current for external output, thereby completing the conversion process from chemical energy to electrical energy. The current collector on a lithium ion battery mainly refers to a metal foil, such as a copper foil, an aluminum foil, etc.

[0004] The current production process of lithium batteries is mainly winding. The winding process requires the current collector to have a certain flexibility and ductility. Porous copper foil can be used as a current collector in lithium batteries to uniform the current density and suppress the generation of lithium dendrites. However, compared with conventional foils, the softness of porous foils is improved, but the tensile strength of the pole piece is reduced, making it difficult to wind in the winding process. SUMMARY

[0005] In view of the above problems, the present application provides a secondary battery, a preparation method thereof, and an electric device, aiming to solve the problem of poor mechanical properties of porous metal foils.

[0006] In a first aspect, the embodiments of the present application provide a secondary battery, comprising an electrode pole piece, the electrode pole piece 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 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 being distributed between the first surface layer and the solid layer, the porosity of the first surface layer being greater than that of the first transition layer; the second porous layer comprises 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 that of the second transition layer.

[0007] The porous metal foil of the embodiments of the present application comprises a three-layer structure combined in the 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. Meanwhile, the porous layer is also distributed with a transition layer at the connection with the solid layer, and the porosity of the transition layer is lower than that of the surface layer in the porous layer, so that the porosity of the porous layer changes in a gradient manner, and the transition of the porous layer to the solid layer is smooth and moderate, which can make the stress distribution of the three-layer structure more uniform and improve the interlayer peeling strength. The current collector using the porous metal foil has better electrical conductivity and mechanical strength, so that the secondary battery has better cycle stability.

[0008] In some embodiments, the porosity of the first surface layer is 65-80%.

[0009] In some embodiments, the porosity of the second surface layer is 65-80%. By controlling the porosity of the first surface layer and the second surface layer within the above range, the porous metal foil can have better mechanical properties, and at the same time, the specific surface area of the porous metal foil is improved, and more active substances can be loaded.

[0010] In some embodiments, the porosity of the first transition layer is 10-40%.

[0011] In some embodiments, the porosity of the second transition layer is 10-40%. By controlling the porosity of the first transition layer and the second transition layer within the above range, the porous layer can have a more suitable gradient change in porosity, and the transition of the porous layer to the solid layer is more smooth and moderate, and the interlayer peeling strength is improved.

[0012] In some embodiments, the thickness of the first porous layer ranges from 50 to 200 μm.

[0013] In some embodiments, the thickness of the second porous layer ranges from 50 to 200 μm. By controlling the thickness of the first porous layer and the second porous layer within the above range, the volume change of the negative active material when lithium is deintercalated can be better relieved.

[0014] In some embodiments, the thickness of the first transition layer ranges from 5 to 30 μm.

[0015] In some embodiments, the thickness of the second transition layer ranges from 5 to 30 μm. By controlling the thickness of the first transition layer and the second transition layer within the above range, the interlayer of the porous metal foil can have a stronger peeling strength.

[0016] 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 have a suitable porosity.

[0017] In some embodiments, 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, and 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. The porous metal foil can be a porous copper foil, or a porous copper alloy foil containing other metal elements, such as a porous manganese-copper alloy foil.

[0018] In some embodiments, the electrode tab is a negative electrode tab.

[0019] In a second aspect, the embodiments of the present application provide a preparation method of a secondary battery, comprising the following steps: preparing a porous metal foil; preparing a negative electrode tab by taking the porous metal foil as a negative electrode current collector, assembling an electrode assembly to obtain a secondary battery; and the step of preparing the porous metal foil comprises the following steps:

[0020] providing a metal multilayer body comprising a first alloy layer, a metal element layer, and a second alloy layer which are sequentially and combined;

[0021] subjecting the metal multilayer body to a first annealing treatment to form a first diffusion layer at the interface between the first alloy layer and the metal element layer, and to form a second diffusion layer at the interface between the second alloy layer and the metal element layer; and obtaining an alloy precursor;

[0022] subjecting the alloy precursor to a phase separation heat treatment, a dealloying treatment, and then a second annealing treatment to form the first surface layer from the first alloy layer, to form the first transition layer from the first diffusion layer, to form the second surface layer from the second alloy layer, and to form the second transition layer from the second diffusion layer, and to obtain the porous metal foil.

[0023] By the above preparation method, the metal multilayer body is subjected to a first annealing treatment to cause interlayer thermal diffusion between the alloy layer and the metal element layer of the metal multilayer body, so that the alloy elements are diffused, the metal elements are diffused from the interlayer interface of the metal multilayer body to a direction away from the interlayer interface, the interlayer interface gradually disappears to form a diffusion layer. Then, the alloy elements are selectively corroded away by dealloying to remove the alloy elements in the alloy layer and the diffusion layer, and part of the removed alloy elements form pores. After annealing, a three-layer porous metal foil with a solid layer is obtained.

[0024] In some embodiments, the thickness of the metal element layer in the rolled metal multilayer body is 20-50 μm. By controlling the thickness of the intermediate metal element layer in the metal multilayer body to be in the range of 20-50 μm, the operation space for subsequent heat treatment is increased, and the mechanical properties of the final porous metal foil are improved.

[0025] In some embodiments, the first annealing treatment is performed at a temperature of 750-850 °C for 10-30 min. The purpose of the first annealing treatment is to make the element segregation of the rolled metal multilayer body, diffuse the alloying elements at the interface between the alloy layer and the metal element layer, and make the alloying elements diffuse deeply into the metal element layer, so that a diffusion layer is formed at the interface, and the rolling orientation and stress are partially or completely eliminated.

[0026] In some embodiments, the second annealing treatment is performed at a temperature of 700-900 °C for 20-60 min in a reducing atmosphere including a mixture of hydrogen and argon. The second annealing treatment is performed in a reducing atmosphere to reduce the oxides in the metal foil after the dealloying treatment, such as reducing copper oxide into copper, and stabilize the crystal structure in the metal foil.

[0027] In a third aspect, the embodiments of the present application provide a power consumption device including the secondary battery of the first aspect. By using the secondary battery of the present application, the working stability of the power consumption device is improved.

[0028] The above description is only a summary of the technical solutions of the present application. In order to enable one skilled in the art to better understand the technical means of the present application, the above description can be implemented according to the content of the specification, and in order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the following specific embodiments of the present application are described. BRIEF DESCRIPTION OF DRAWINGS

[0029] Various other advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The accompanying drawings are intended to depict only preferred embodiments of the application, and therefore should not be considered to narrow the scope of the present application in any way. Instead, they are included to provide illustration of the preferred embodiments of the present application. In the drawings:

[0030] FIG. 1 is a schematic structural diagram of a porous metal foil according to an embodiment of the present application;

[0031] FIG. 2 is a cross-sectional electron microscope image (800 times) of the porous metal foil according to Embodiment 1 of the present application;

[0032] FIG. 3 is a cross-sectional electron microscope image (2000 times) of the porous metal foil according to Embodiment 1 of the present application;

[0033] FIG. 4 is a cross-sectional electron microscope image (800 times) of the porous metal foil according to Embodiment 13 of the present application;

[0034] Figure 5 is a cross-sectional electron micrograph (2000x) of the porous metal foil of Example 13 of the present application;

[0035] Figure 6 is a cross-sectional electron micrograph (800x) of the porous metal foil of Comparative Example 1 of the present application;

[0036] Figure 7 is a cross-sectional electron micrograph (2000x) of the porous metal foil of Comparative Example 1 of the present application;

[0037] Figure 8 is a cross-sectional EDS line scan of the corresponding cold-rolled sheet of the porous metal foil of Example 1 of the present application;

[0038] Figure 9 is a cross-sectional EDS line scan of the corresponding cold-rolled sheet of the porous metal foil of Example 1 of the present application after crystallization annealing treatment;

[0039] Figure 10 is a cross-sectional EDS line scan of the corresponding cold-rolled sheet of the porous metal foil of Example 1 of the present application after crystallization annealing treatment and phase separation heat treatment;

[0040] Figure 11 is a cross-sectional EDS line scan of the corresponding cold-rolled sheet of the porous metal foil of Example 1 of the present application after crystallization annealing treatment, phase separation heat treatment, dealloying and reduction annealing; Note: Mn (at%) represents the EDS line scan of Mn (at%), Cu (at%) represents the EDS line scan of Cu (at%);

[0041] Figure 12 is a schematic structural diagram of a secondary battery according to some embodiments of the present application;

[0042] Figure 13 is a schematic structural diagram of a battery cell according to some embodiments of the present application;

[0043] Figure 14 is a schematic diagram of a battery module according to some embodiments of the present application;

[0044] Figure 15 is a schematic diagram of a battery pack according to some embodiments of the present application;

[0045] Figure 16 is an exploded view of the battery pack of some embodiments of the present application shown in Figure 15;

[0046] Figure 17 is a schematic structural diagram of an electrode assembly according to some embodiments of the present application;

[0047] Figure 18 is a schematic structural diagram of an electric device according to some embodiments of the present application.

[0048] The reference signs in the detailed description of the embodiments are as follows: 01 - housing; 02 - cover plate; 03 - electrode assembly; 04 - battery cell; 05 - battery module; 06 - upper box body; 07 - lower box body; 101 - negative electrode tab; 102 - positive electrode tab; 201 - negative electrode tab; 202 - positive electrode tab; 203 - separator; 40 - secondary battery; 50 - electric device; 501 - controller; 502 - motor; 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 DESCRIPTION

[0049] The embodiments of the technical solutions of the present application will be described in detail below with reference to the drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present application, and therefore only serve as examples, and cannot limit the protection scope of the present application.

[0050] 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 belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "include" and "have" and any variations thereof in the specification and claims of the present application and the above description of drawings are intended to cover non-exclusive inclusion.

[0051] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly and specifically limited.

[0052] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the present application. The appearance of the phrase in various places in the specification does not necessarily all refer to the same embodiment, nor is it necessarily mutually exclusive or alternative to other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0053] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone. In addition, the character " / " in this paper generally represents a "or" relationship between the front and rear associated objects.

[0054] In the description of the embodiments of the present application, the term "a plurality of" refers to two or more (including two), and similarly, "a plurality of groups" refers to two or more groups (including two groups), and "a plurality of pieces" refers to two or more pieces (including two pieces).

[0055] In the description of the embodiments of the present 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" and the like indicate the orientation or positional relationship shown in the drawings, which is only for the convenience of describing the embodiments of the present application and simplifying the description, and does not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0056] In the description of the embodiments of the present application, unless otherwise explicitly specified and limited, the technical terms "mounting", "connection", "connection", "fixing" and the like should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or it can be integrated; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the internal communication of two elements or the interaction relationship between two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0057] The tensile strength and porosity of the porous metal have an inverse relationship, that is, the higher the porosity, the lower the tensile strength. At the same time, intergranular corrosion existing in the metal can destroy the bonding between the grains, greatly reducing the mechanical strength of the metal. Due to the intergranular corrosion and stress accumulation of the porous structure, the porous structure often has the problems of low tensile strength and poor interlayer peeling strength.

[0058] Based on this, the embodiments of the present application provide a secondary battery, which comprises an electrode tab, and the electrode tab comprises a porous metal foil, as shown in FIG. 1, the porous metal foil comprises a first porous layer 100, a solid layer 200 and a second porous layer 300, the solid layer 200 is laminated and combined 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 comprises a first surface layer 110 and a first transition layer 120, the first transition layer 120 is distributed between the first surface layer 110 and the solid layer 200, and the porosity of the first surface layer 110 is greater than that of the first transition layer 120; the second porous layer 300 comprises a second surface layer 310 and a second transition layer 320, the second transition layer 320 is distributed between the second surface layer 310 and the solid layer 200, and the porosity of the second surface layer 310 is greater than that of the second transition layer 320.

[0059] The porous metal foil of the embodiments of the present application comprises a three-layer structure combined in the manner of "first porous layer / solid layer / second porous layer". The solid layer refers to a layer with a dense structure in its material, a tight 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. At the same time, the porous layer also comprises a surface layer and a transition layer, i.e. a transition layer is distributed on the side of the porous layer close to the solid layer, and the porosity of the transition layer is lower than that of the surface layer, which makes the porous layer present a continuous or phased change, i.e. the porosity of the porous layer changes from high to low in a phased or continuous manner from the side far from the solid layer to the side adjacent to the solid layer. Due to the gradient change of the porosity of the porous layer, the transition between the porous layer and the solid layer is smooth and moderate, which can make the stress distribution of the three-layer structure of the porous metal foil more uniform, and improve the interlayer peeling strength. When the porous metal foil is subjected to external forces such as winding, tension and pressure, the peeling strength between the porous layer and the solid layer is higher, and the mechanical properties are better.

[0060] 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 point value between any two of them.

[0061] 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%, 80% or a range point value between any two of them. If the surface layer porosity of the porous layer is too low (<65%), it cannot carry enough active substances, and cannot improve the battery capacity; if the surface layer porosity of the porous layer is too high (>80%), it will cause the mechanical properties of the porous foil to decrease. Controlling the porosity of the first surface layer and the second surface layer within the above range can make the porous metal foil have better mechanical properties, and further improve the specific surface area of the porous metal foil, so as to provide a larger reaction interface, load more active substances, and improve the capacity and power of the battery.

[0062] 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 a range point value between any two of them.

[0063] In some embodiments, the porosity of the second transition layer is in the range of 10-40%. As an example, the porosity of the second transition layer can be any one of 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range between any two of them.

[0064] In some embodiments, the thickness of the first porous layer is in the range of 50-200 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, 200 μm or a range between any two of them.

[0065] In some embodiments, the thickness of the second porous layer is in the range of 50-200 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, 200 μm or a range between any two of them. Controlling the thickness of the first porous layer and the second porous layer in the above range can load more negative active materials. In addition, the negative active material will expand or shrink in structure due to the deintercalation of lithium during the charging and discharging process. Taking the silicon-based negative electrode material as an example, the silicon-based negative electrode material will cause strong crystal reconstruction and phase change of the material itself during the deintercalation of lithium, resulting in a huge volume change, and thus the performance of the electrode material is reduced. When the porous layer has the thickness in the above range, the volume change of the negative active material during the intercalation and deintercalation of lithium can be better relieved.

[0066] In some embodiments, the thickness of the first transition layer is in the range of 5-30 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, 30 μm or a range between any two of them.

[0067] 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, 30 μm, or a range between any two of them. If the thickness of the transition layer is too large, the porosity of the porous layer will be reduced, and the thickness of the solid layer will also be reduced, which will affect 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 be able to improve the interface peeling strength. Therefore, controlling the thickness of the first transition layer and the second transition layer within the above range can both improve the interface peeling strength of the porous metal foil and make the porous metal foil have a suitable porosity.

[0068] In some embodiments, the thickness of the solid layer ranges from 2 to 28 μm. For example, in the porous metal foil of the embodiments of the present application, the thickness of the solid layer includes but is not limited to any one of 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, 28 μm, or a range between any two of them. If the thickness of the solid layer is higher than 28 μm, the overall porosity of the porous metal foil will be reduced, and thus the reaction interface of the porous metal foil will be reduced. If the thickness of the solid layer is less than 2 μm, it will not be able to strengthen the mechanical properties of the porous layer. Therefore, setting the solid layer within a suitable range can both improve the tensile strength of the porous metal foil and make the porous metal foil have a suitable porosity.

[0069] In some embodiments, the material of the first porous layer includes at least one of copper element, manganese copper alloy, copper aluminum alloy, copper zinc alloy, and copper nickel alloy.

[0070] In some embodiments, the material of the solid layer includes copper element.

[0071] In some embodiments, the material of the second porous layer includes at least one of copper element, 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 metal elements, such as a porous manganese copper alloy foil.

[0072] In some embodiments, the electrode tab is a negative electrode tab.

[0073] In a second aspect, the embodiments of the present application provide a method for preparing a secondary battery, including the following steps: preparing a porous metal foil; preparing a negative electrode tab by taking the porous metal foil as a negative electrode current collector, assembling an electrode assembly to obtain a secondary battery; the step of preparing the porous metal foil includes the following:

[0074] S1: providing a metal multilayer body, the metal multilayer body comprising a first alloy layer, a metal element layer and a second alloy layer which are sequentially stacked and bonded;

[0075] S2: subjecting the metal multilayer body to a first annealing treatment; forming a first diffusion layer at the interface between the first alloy layer and the metal element layer, and forming a second diffusion layer at the interface between the second alloy layer and the metal element layer; obtaining an alloy precursor;

[0076] S3: subjecting the alloy precursor to a phase separation heat treatment, a dealloying treatment, and then a second annealing treatment, so as 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, and obtain a porous metal foil.

[0077] The preparation method of the embodiment first performs deep layer compounding between the alloy plate and the pure metal plate in the metal multilayer body through the first annealing treatment. During this period, deep interdiffusion occurs between the alloy plate and the pure metal plate, that is, interatomic diffusion occurs at the contact interface between the alloy plate and the pure metal plate, and the metal atoms on both sides of the interface diffuse to the other side to form a diffusion layer. Through interatomic diffusion, a firm bonding layer is formed, thereby forming plate materials bonded at the atomic level. The alloying elements change from high to low in stages or continuously from the surface layer of the alloy layer to the side close to the metal element layer. Then, the metal multilayer body is subjected to a phase separation heat treatment to precipitate α phase, so as to facilitate the dealloying to obtain a porous copper with structural self-supporting ability. Then, the dealloying treatment selectively corrodes away the alloying elements, and part of the removed alloying elements form pores. After annealing, a three-layer porous metal foil with a solid reinforcing layer is obtained.

[0078] The steps of preparing the porous metal foil will be described in detail below.

[0079] Step S1: providing a metal multilayer body, the metal multilayer body comprising a first alloy layer, a metal element layer and a second alloy layer which are sequentially stacked and bonded.

[0080] In some embodiments, the preparation method of the metal multilayer body comprises the following steps: polishing the alloy plate and the pure metal plate respectively, then bonding the polished surfaces, stacking them in the order of "alloy plate / pure metal plate / alloy plate", and then performing vacuum electron beam sealing welding to obtain the metal multilayer body.

[0081] In some embodiments, the power density of the vacuum electron beam sealing welding is 1000-1500 kW / cm 2 , and the vacuum degree is <5 Pa.

[0082] In some embodiments, the alloy sheet is selected from at least one of a manganese-copper alloy sheet, a copper-aluminum alloy sheet, a copper-zinc alloy sheet, and a copper-nickel alloy sheet. As an example, a method of preparing a manganese-copper alloy sheet 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 by a vacuum induction melting method. Cutting to a certain size, and polishing and cleaning.

[0083] In some embodiments, the process conditions of the vacuum induction melting are as follows: melting at 1000-1200°C for 1-5h under an argon atmosphere.

[0084] In some embodiments, the polishing is to a roughness Ra value of micrometer level (1-100pm).

[0085] 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%, 85%, or a range point value between any two of them. 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%, 30%, or a range point value between any two of them. Controlling the atomic percentage of manganese atoms and copper atoms in the manganese-copper alloy within the above range results in a porous metal foil with more suitable porosity.

[0086] In some embodiments, the thickness ratio of the first alloy layer, the metal monomer layer, and the second alloy layer in the metal multilayer body is (2-8):1:(2-8). As an example, the thickness ratio of the first alloy layer, the metal monomer 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, 8:1:2, or a range point value between any two of them. Controlling the thickness ratio of the first alloy layer, the metal monomer layer, and the second alloy layer within the above range can make the prepared porous metal foil have both better mechanical properties and higher porosity.

[0087] In some embodiments, the metal multilayer body is further subjected to a hot rolling process during preparation. The steps of the hot rolling process are as follows: heating and holding the metal multilayer body in an inert gas environment, and then hot rolling to reduce the material thickness to below 6mm.

[0088] In some embodiments, the temperature of the hot rolling is 780-820 °C, and the holding time is 0.5-1 h; the thickness of the hot-rolled plate is in the range of 3-6 mm. As an example, the temperature of the hot rolling includes but is not limited to any one of 780 °C, 790 °C, 800 °C, 810 °C, 820 °C, or a range between any two of them. The holding time is subject to the specific production needs, and includes but is not limited to any one of 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, or a range between any two of them. The hot rolling process is used to combine the alloy plate and the elemental metal plate in the metal multilayer body to form a hot-rolled plate that is bonded at the atomic level.

[0089] In a specific embodiment, the hot rolling of the metal multilayer body of step S1 is performed by heating the metal multilayer body in an inert gas environment at 800 °C for 1 h, and then immediately performing hot rolling to reduce the thickness of the material to 5 mm to obtain a hot-rolled plate.

[0090] In some embodiments, the metal multilayer body is further subjected to a cold rolling process during the preparation process. The cold rolling process includes subjecting the metal multilayer body to multiple passes of cold rolling to reduce the thickness. The cold rolling process can be performed after the hot rolling process.

[0091] In some embodiments, the cold rolling can have a tonnage of 1000 T (tons), and a single reduction rate of 25-35%. As an example, the single reduction rate of the cold rolling includes but is not limited to any one of 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range between any two of them. The reduction rate of the cold rolling has an effect on the surface roughness and tensile strength of the cold-rolled plate. The greater the reduction rate, the smaller the surface roughness of the cold-rolled plate. However, if the reduction rate is too large (> 35%), it will be detrimental to the tensile strength of the material. Controlling the single reduction rate of the cold rolling in the above range can obtain a cold-rolled plate with low surface roughness and good tensile strength.

[0092] 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.

[0093] 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.

[0094] 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, any one of 750°C, 760°C, 770°C, 780°C, 790°C, 800°C, 810°C, 820°C, 830°C, 840°C, and 850°C, 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] The following is a detailed description of the secondary battery and its components.

[0102] Figure 12 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 functional outputs. 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.

[0103] Figure 13 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. As shown in Figure 13, 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, and a separator is placed between them to provide 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.

[0104] Referring to Figure 14, which shows an example 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 manner. Furthermore, these multiple battery cells 04 can be secured using fasteners.

[0105] Optionally, the battery module may also include a housing with a receiving space in which multiple battery cells 04 are received.

[0106] Referring to Figures 15 and 16, which serve as 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 compartment 06 and a lower compartment 07, with the upper compartment 06 covering the lower compartment 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.

[0107] Please refer to Figure 17, which is a schematic diagram of the structure of electrode assembly 03 in some embodiments of this application. Electrode assembly 03 is the component in the battery cell 04 where the electrochemical reaction occurs. 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.

[0108] 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.

[0109] 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.

[0110] 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.

[0111] 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.

[0112] 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).

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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.

[0117] Please refer to Figure 18, which is a structural schematic diagram 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.

[0118] 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.

[0119] The following description is based on specific embodiments.

[0120] 1. Examples of porous metal foil

[0121] Example A1

[0122] 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.

[0123] 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%.

[0124] 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.

[0125] This application provides a porous metal foil, the preparation method of which includes the following steps:

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] Example A2

[0132] 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%.

[0133] 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).

[0134] Example A3

[0135] 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%.

[0136] 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).

[0137] Example A4

[0138] 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.

[0139] 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.

[0140] Example A5

[0141] 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.

[0142] 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.

[0143] Example A6

[0144] 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.

[0145] 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.

[0146] Example A7

[0147] 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.

[0148] 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.

[0149] Example A8

[0150] 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.

[0151] 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.

[0152] Example A9

[0153] 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.

[0154] 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.

[0155] Example A10

[0156] 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.

[0157] 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.

[0158] Example A11

[0159] 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.

[0160] 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.

[0161] Example A12

[0162] 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.

[0163] 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.

[0164] Example A13

[0165] 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.

[0166] 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.

[0167] Comparative Example A1

[0168] 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.

[0169] 2. Battery Example

[0170] Example B1 and Comparative Example B1

[0171] 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:

[0172] (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.

[0173] (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.

[0174] (3) A polyethylene film is used as a separator (coated with a ceramic layer and a polymer layer).

[0175] (4) In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), the electrolyte is 1M LiFSI (solvent is ethylene glycol dimethyl ether).

[0176] (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".

[0177] Performance testing

[0178] To verify the progressiveness of the embodiments of this application, the samples of the embodiments and comparative examples were subjected to the following tests:

[0179] 1. Testing the porosity of porous metal foil.

[0180] 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.

[0181] 2. Thickness test of porous metal foil.

[0182] 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.

[0183] 3. Tensile strength test.

[0184] 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.

[0185] The formula for calculating tensile strength is: σ = F1 / S, where S is the original cross-sectional area of ​​the specimen, in mm. 2 .

[0186] 4. Test of normal peel force.

[0187] 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.

[0188] 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.

[0189] 5. Cross-sectional morphology observation.

[0190] 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.

[0191] The test results for items 1-5 above are shown in Tables 1 and 2.

[0192] 6. Battery cycle performance test.

[0193] 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.

[0194] Table 1

[0195] 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.

[0196] Table 2

[0197] Table 3

[0198] The test results show that, as shown in Figure 2, 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, recrystallization heat treatment (800℃ / 20 min / water cooling), phase separation heat treatment (650℃ / 150 min / furnace cooling), and dealloying and reduction annealing can appropriately retain the solid intermediate layer of the three-layer porous copper structure, which can enhance the tensile strength (15.7 MPa). Figure 4 shows a cross-sectional electron microscope image of the porous metal foil in Example A13. When the recrystallization heat treatment is extended from 20 min to 40 min, the manganese in the precursor diffuses excessively, and only a very thin area of ​​the intermediate layer is basically not diffused by manganese. Thus, after dealloying and reduction annealing, the solid intermediate layer of the three-layer porous copper structure becomes thinner, and in some places the solid layer is no longer visible, resulting in a decrease in tensile strength (8.1 MPa). Figure 6 shows a cross-sectional electron microscope image of the porous metal foil in Comparative Example A1. When the thickness of the intermediate layer of the metal multilayer was reduced from 21 μm to 13 μm, under the same heat treatment and dealloying conditions, the manganese in the precursor diffused excessively, meaning that manganese diffused fully 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 of the three-layer porous copper structure, accompanied by the generation of cracks, may be related to stress accumulation in the intermediate layer.

[0199] Figures 8-11 are cross-sectional EDS line scans of Example A1, corresponding to the cross-sectional elemental changes of the porous copper structure with solid layers. As shown in Figure 8, the middle layer of the metal multilayer is basically pure copper, with a clear elemental gradient between it and the alloy layers on both sides. As shown in Figure 9, after recrystallization annealing heat treatment, the thickness of the middle pure copper layer of the metal multilayer becomes thinner, and the interlayer elemental gradient slows down, indicating that elemental diffusion has occurred. As shown in Figure 10, after recrystallization heat treatment and phase separation heat treatment, the thickness of the middle pure copper layer of the metal multilayer becomes thinner or even disappears, the interlayer elemental gradient slows down further, and elemental diffusion is more complete. As shown in Figure 11, after recrystallization heat treatment, phase separation heat treatment, dealloying, and reduction annealing, the plateau of the middle pure copper layer reappears, and the two sides also become copper layers, but there is a certain amount of manganese residue between the layers. This indicates that a structure with copper as the main component was obtained through dealloying and reduction annealing.

[0200] 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.

[0201] 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.

[0202] 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 1 or 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 any one of claims 1 to 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.

Images