Copper foil, method for manufacturing the same, electrode sheet, and secondary battery

Abstract

The application provides a copper foil and a preparation method thereof, a pole piece and a secondary battery. The copper foil comprises a copper foil base body and a porous copper layer arranged on at least one side surface of the copper foil base body. The porous copper layer comprises a plurality of pores, at least part of the pores are interconnected and form a three-dimensional network structure, and the average pore diameter of the pores is 40 nm to 200 nm. The copper foil provided by the application can balance the tensile strength and the elongation rate, and can well meet the requirements of the stress intensity and the stress buffering of the current collector.

Description

Technical Field

[0001] This application relates to the field of copper foil technology, and in particular to copper foil and its preparation methods, electrodes, and secondary batteries. Background Technology

[0002] In recent years, with the rapid development of secondary batteries, represented by lithium-ion batteries, towards higher energy density, longer cycle life, and higher rate performance, the development of current collectors with three-dimensional porous structures (such as porous copper foil) has become a research hotspot in the industry. Currently, the mainstream technical routes for preparing porous copper foil mainly include template method, direct electrodeposition method, surface etching method, and composite processing method. However, porous copper foil prepared by current methods often suffers from large pore size and / or wide pore size distribution, making it difficult to simultaneously achieve high tensile strength and elongation, thus failing to adequately meet the requirements for stress strength and stress buffering as a current collector. Summary of the Invention

[0003] Based on this, this application provides a copper foil and its preparation method, an electrode, and a secondary battery. The copper foil can balance tensile strength and elongation, and can well meet the requirements of stress strength and stress buffering as a current collector.

[0004] The first aspect of this application provides a copper foil, including a copper foil substrate and a porous copper layer disposed on at least one surface of the copper foil substrate. The porous copper layer contains a plurality of channels, at least some of which are interconnected to form a three-dimensional mesh structure. The average pore size of the channels is 40 nm to 200 nm.

[0005] In some embodiments, the porous copper layer is provided on both sides of the copper foil substrate, wherein the porous copper layer on one side is a first porous copper layer and the porous copper layer on the other side is a second porous copper layer. The average pore diameter of the channels in the first porous copper layer is greater than the average pore diameter of the channels in the second porous copper layer, and the porosity of the first porous copper layer is greater than the porosity of the second porous copper layer.

[0006] In some implementations, one or more of the following conditions are satisfied:

[0007] (1) The ratio of the average pore diameter of the channels in the first porous copper layer to the average pore diameter of the channels in the second porous copper layer is (1.2~4):1;

[0008] (2) The average pore size of the channels in the first porous copper layer is 30nm~180nm, and the average pore size of the channels in the second porous copper layer is 40nm~60nm;

[0009] (3) The porosity of the first porous copper layer is 5%~20%, and the porosity of the second porous copper layer is 5%~15%.

[0010] In some implementations, one or more of the following conditions are satisfied:

[0011] (1) The depth of the channel is 10nm~300nm;

[0012] (2) The thickness of the porous copper layer is 100nm~350nm.

[0013] (3) The interface expansion area ratio Sdr of the copper foil is 0.6~1.3;

[0014] (4) The surface roughness Ra of the copper foil is 0.18μm~0.40μm, and Rz is 1.0μm~1.3μm;

[0015] (5) The content of other metallic elements in the copper foil is ≤0.1mg / m 2 The other metallic elements include one or more of zinc, tin, manganese, zirconium, and aluminum.

[0016] A second aspect of this application provides a method for preparing copper foil, comprising:

[0017] Provide copper foil substrate;

[0018] A precursor layer is constructed on at least one surface of the copper foil substrate. The precursor layer comprises a copper alloy, which includes copper and a removable metal element, wherein the removable metal element includes one or more of zinc, tin, manganese, zirconium, and aluminum.

[0019] The precursor layer is subjected to a dealloying process to remove the removable metal element from the precursor layer, thereby preparing a porous copper layer containing multiple channels. At least some of the channels are interconnected to form a three-dimensional network structure, and the average pore size of the channels is 40nm~200nm.

[0020] In some implementations, one or more of the following conditions are satisfied:

[0021] (1) The content of the removable metal element in the precursor layer is 50 mg / m³. 2 ~220mg / m 2 ;

[0022] Optionally, the precursor layer is constructed on both sides of the copper foil substrate, wherein the precursor layer on one side is a first precursor layer and the precursor layer on the other side is a second precursor layer, and the content of the removable metal element in the first precursor layer is greater than the content of the removable metal element in the second precursor layer.

[0023] Optionally, the content of the removable metal element in the first precursor layer is 50 mg / m³. 2 ~220mg / m 2 The content of the removable metal element in the second precursor layer is 100 mg / m³. 2 ~130mg / m 2 ;

[0024] (2) The removable metal element is zinc.

[0025] In some embodiments, the step of constructing a precursor layer on at least one surface of the copper foil substrate includes:

[0026] The precursor layer is constructed on at least one surface of the copper foil substrate by electroplating.

[0027] Optionally, the electroplating solution includes a copper source and a removable metal source;

[0028] Alternatively, the molar ratio of the copper source to the removable metal source is (0.5~6):1;

[0029] Alternatively, the concentration of the copper source is 0.1 mol / L to 0.3 mol / L;

[0030] Alternatively, the concentration of the removable metal source is 0.05 mol / L to 0.2 mol / L;

[0031] Optionally, the pH value of the electroplating solution is 10-13;

[0032] Optionally, the current density of the electroplating is 0.1 A / dm³. 2 ~10A / dm 2 0.5A / dm is optional. 2 ~5A / dm 2 ;

[0033] Optionally, the electroplating time is 20s to 240s.

[0034] In some embodiments, the electroplating solution further comprises one or more of a complexing agent, a leveling agent, and a pH adjuster;

[0035] Optionally, the complexing agent includes one or more of sodium citrate, disodium EDTA, glycine, sodium potassium tartrate, triethanolamine, and potassium pyrophosphate; optionally, it includes sodium citrate and glycine.

[0036] Optionally, the concentration of the complexing agent is 1 g / L to 50 g / L;

[0037] Optionally, the leveling agent includes one or more of xylitol, polyethylene glycol, gelatin, guar gum, hydroxyethyl cellulose, polyethyleneimine, and thiourea derivatives;

[0038] More preferably, the leveling agent comprises xylitol and guar gum; more preferably, the mass ratio of guar gum to xylitol is (5~80):1;

[0039] Optionally, the concentration of the leveling agent is 1 g / L to 100 g / L;

[0040] Optionally, the pH adjuster includes one or more of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrochloric acid, and boric acid; sodium hydroxide may be selected as the pH adjuster.

[0041] Optionally, the concentration of the pH adjuster is 20 g / L to 150 g / L.

[0042] In some embodiments, the dealloying process includes sequential alkaline and acid treatments, satisfying one or more of the following conditions:

[0043] (1) The alkaline treatment includes: soaking the precursor layer in an alkaline solution for 1 h to 15 h;

[0044] Optionally, the alkaline solution includes one or more of NaOH, KOH, NaHCO3, and NH3·H2O;

[0045] Alternatively, in the alkaline solution, the mass content of NaOH is 5wt%~10wt%, the mass content of KOH is 5wt%~10wt%, the mass content of NaHCO3 is 10wt%~20wt%, and the mass content of NH3·H2O is 2wt%~4wt%.

[0046] (2) The acid treatment includes: immersing the precursor layer after the alkali treatment in an acidic solution for 1 min to 60 min;

[0047] Optionally, the acidic solution includes one or both of hydrochloric acid and sulfuric acid;

[0048] Alternatively, the concentration of the hydrochloric acid is 2 mol / L to 4 mol / L, the concentration of the sulfuric acid is 2 mol / L to 4 mol / L, and the volume ratio of the hydrochloric acid to the sulfuric acid is (1 to 2):1.

[0049] A third aspect of this application provides an electrode sheet comprising a current collector and an active layer disposed on at least one side of the current collector, wherein the current collector comprises the copper foil described in the first aspect or a copper foil prepared by the preparation method described in the second aspect.

[0050] In some embodiments, the active material in the active layer includes a silicon-based material; optionally, the silicon-based material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

[0051] A fourth aspect of this application provides a secondary battery comprising the electrode described in the third aspect.

[0052] Among the copper foils mentioned above, the three-dimensional mesh structure can give the copper foil a higher elongation, allowing it to accommodate greater volume changes and providing better stress buffering. This can effectively alleviate the volume expansion of active materials, especially easily expanding silicon-based materials, during charging and discharging, reducing electrode pulverization and detachment. At the same time, the small aperture and narrow distribution of these channels, with an average pore size of 40nm~200nm, ensures that the expansion stress borne by the channels is basically uniform, resulting in uniform deformation of the overall structure. This reduces the likelihood of local collapse or cracking, which helps the copper foil maintain high tensile strength and allows it to well meet the stress strength requirements of a current collector. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the structure of a copper foil according to one embodiment of this application.

[0054] Figure 2 This is a schematic diagram of the structure of a copper foil according to another embodiment of this application.

[0055] Figure 3 The image shows the X-ray energy dispersive X-ray (EDX) mapping of the precursor layer obtained after electroplating in Example 1.

[0056] Figure 4 This is an EDX mapping image of the copper foil obtained after the dealloying treatment in Example 1.

[0057] Figure 5 This is a scanning electron microscope (SEM) image of the cross-section of the copper foil obtained after the dealloying treatment in Example 3.

[0058] Figure 6 The images shown are SEM images of the copper foils prepared in Examples 1-2, 5, and 7; (a) is an SEM image of the copper foil prepared in Example 1, (b) is an SEM image of the copper foil prepared in Example 2, (c) is an SEM image of the copper foil prepared in Example 5, and (d) is an SEM image of the copper foil prepared in Example 7.

[0059] Reference numerals: 1 Copper foil substrate; 2 Porous copper layer; 20 Channel; 21 First porous copper layer; 22 Second porous copper layer. Detailed Implementation

[0060] To facilitate understanding of this application, a more complete description will be provided below. However, this application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0061] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0062] 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 terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. It should be noted that, unless otherwise stated, the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items, "above," "below," includes the stated number, and "one or more" with "multiple" means two or more.

[0063] In this document, when referring to numerical intervals (i.e., numerical ranges), unless otherwise specified, the distribution of selectable values ​​within a numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the numerical interval, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints, which is equivalent to directly listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, ratio, etc. The term "numerical interval" can be broadly included to include percentage intervals, ratio intervals, proportion intervals, and other numerical interval types.

[0064] In this document, for methods involving multiple steps, unless otherwise explicitly stated herein, there is no strict order constraint on the execution of these steps; they may be executed in any order other than those described. Moreover, any step may include multiple sub-steps or multiple stages, which are not necessarily completed at the same time, but may be executed at different times, and their execution order is not necessarily sequential, but may be executed in turn, alternately, or simultaneously with other steps or parts of the sub-steps or stages of other steps.

[0065] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0066] In recent years, with the rapid development of secondary batteries, represented by lithium-ion batteries, towards higher energy density, longer cycle life, and higher rate performance, the development of current collectors with three-dimensional porous structures has become a research hotspot in the industry. Porous current collectors can effectively increase the loading of active materials, provide abundant ion transport channels, and buffer the volume expansion of active materials, especially easily expandable silicon-based materials, during charge and discharge. Currently, the mainstream technical routes for preparing porous copper foils mainly include template methods, direct electrodeposition methods, surface etching methods, and composite processing methods. However, porous current collectors prepared using current methods often suffer from large pore sizes and / or wide pore size distributions, making it difficult for the copper foil to simultaneously achieve tensile strength and elongation, thus failing to adequately meet the requirements for stress strength and stress buffering (such as buffering the volume expansion of active materials) as a current collector. In view of this, this application proposes the following technical solution.

[0067] Firstly, this application provides a copper foil, see [link to relevant documentation]. Figure 1 The copper foil substrate 1 includes a porous copper layer 2 disposed on at least one side surface of the copper foil substrate 1. The porous copper layer 2 includes a plurality of channels 20, at least some of which are interconnected to form a three-dimensional network structure. The average pore size of the channels 20 is 40 nm to 200 nm.

[0068] For example, the average aperture of the channel 20 can be 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, or within any of the above values.

[0069] The copper foil provided in this application includes a porous copper layer 2. At least some of the channels 20 in the porous copper layer 2 are interconnected, forming a three-dimensional network structure that provides a large internal surface area and storage space. This allows the copper foil to carry more active material per unit area, thereby improving the overall energy density of the battery. Simultaneously, the channels 20 of this three-dimensional network structure impart a higher elongation to the copper foil, enabling it to accommodate greater volume changes and providing better stress buffering. This effectively alleviates the volume expansion of active materials, especially easily expanding silicon-based materials, during charging and discharging, reducing electrode pulverization and detachment. Furthermore, the interconnected channels 20 in the three-dimensional network structure allow the electrolyte to fully wet the electrode interior, achieving "three-dimensional ion transport," reducing interfacial charge transfer impedance, and reducing concentration polarization, thus giving the battery higher rate performance. Additionally, the channels 20 of the three-dimensional network structure provide a large electrochemical reaction surface area, effectively reducing local current density and reducing or even preventing the formation of lithium dendrites on the surface, which is beneficial for reducing or even avoiding lithium dendrite formation.

[0070] Based on this, when the average pore size of the channel 20 is 40nm~200nm, this nanoscale small-pore size and narrow distribution (uniform pore size distribution) channel 20 can provide more support points, allowing the expansion stress of the active material to be dispersed across a large number of micropore walls, reducing stress concentration, and thus better achieving the stress buffering effect for the volume expansion of the active material. Simultaneously, this small-pore size and narrow distribution of the channel 20 ensures that the expansion stress borne by the channel 20 is basically uniform, resulting in uniform deformation of the overall structure and reducing the likelihood of local collapse or cracking. This helps the copper foil maintain high tensile strength, enabling it to well meet the stress strength requirements as a current collector. Furthermore, it facilitates the electrolyte wetting deep into the pores, resulting in less concentration polarization.

[0071] In some embodiments, the depth of the channel 20 is 10 nm to 300 nm. For example, the depth of the channel 20 can be 10 nm, 30 nm, 50 nm, 80 nm, 100 nm, 130 nm, 150 nm, 170 nm, 200 nm, 230 nm, 250 nm, 280 nm, 300 nm, or within any of the above values.

[0072] Non-limiting, the parameters of the channels 20 in the porous copper layer 2 (such as average pore diameter, depth, etc.) can be tested using the following method: A scanning electron microscope (SEM) is used to test the cross-section of the porous copper layer 2. The pore diameter of all channels 20 within a unit area (e.g., 1 mm × 1 mm) in a certain region is measured, and the average value is taken as the pore diameter of that measurement region. Multiple measurement regions are tested, and the average value of these multiple measurement regions is taken as the average pore diameter of the channel 20. The method for measuring the depth of the channel 20 is similar. The depth of the channel 20 refers to the distance between the highest and lowest points of the channel 20 along the thickness direction of the porous copper foil. (See [reference needed]). Figure 1 The "D" in it.

[0073] In some embodiments, the thickness of the porous copper layer 2 is 100nm to 350nm. For example, the thickness of the porous copper layer 2 can be 100nm, 130nm, 150nm, 170nm, 200nm, 230nm, 250nm, 280nm, 300nm, 320nm, 350nm, or within any range of the above values.

[0074] In some implementations, see Figure 2 Porous copper layers are provided on both sides of the copper foil substrate 1. The porous copper layer on one side is the first porous copper layer 21, and the porous copper layer on the other side is the second porous copper layer 22. The average pore diameter of the channels 20 in the first porous copper layer 21 is greater than the average pore diameter of the channels 20 in the second porous copper layer 22, and the porosity of the first porous copper layer 21 is greater than the porosity of the second porous copper layer 22.

[0075] Furthermore, the ratio of the average pore diameter of the channel 20 in the first porous copper layer 21 to the average pore diameter of the channel 20 in the second porous copper layer 22 is (1.2~4):1. For example, this ratio can be 1.2:1, 1.8:1, 2:1, 2.4:1, 3:1, 3.6:1, 4:1, or within any of the above values.

[0076] Furthermore, the average pore size of the channels 20 in the first porous copper layer 21 is 30nm to 180nm, and the average pore size of the channels 20 in the second porous copper layer 22 is 40nm to 60nm. For example, the average pore size of the channels 20 in the first porous copper layer 21 can be 30nm, 50nm, 70nm, 90nm, 110nm, 130nm, 150nm, 180nm, or within any range of the above values; the average pore size of the channels 20 in the second porous copper layer 22 can be 40nm, 44nm, 50nm, 56nm, 60nm, or within any range of the above values.

[0077] This bifacial heterostructure (asymmetric structure) with a relatively small pore size, narrow distribution, and low porosity on one side, combined with a relatively large pore size, wide distribution, and high porosity on the other, allows for matched optimization design of the positive and negative electrode interfaces. This adapts to the differentiated needs of different electrode interfaces (such as the construction of the negative electrode SEI film and the modification of the positive electrode interface). It can also effectively mitigate the volume expansion of active materials, especially silicon-based negative electrode materials, while maintaining electrolyte wettability. Furthermore, it is beneficial for meeting diverse needs, ranging from high-rate batteries (requiring relatively small pore size, narrow distribution, and low porosity to meet high strength requirements) to high-energy-density batteries (requiring relatively large pore size, wide distribution, and high porosity to meet high load requirements).

[0078] Furthermore, the porosity of the first porous copper layer 21 is 5% to 20%, and the porosity of the second porous copper layer 22 is 5% to 15%. For example, the porosity of the first porous copper layer 21 can be 5%, 8%, 11%, 13%, 15%, 17%, 20%, or any value within the range above; the porosity of the second porous copper layer 22 can be 5%, 8%, 10%, 12%, 14%, 15%, or any value within the range above. This bifacial heterostructure (asymmetric structure) with a relatively small porosity on one side and a relatively large porosity on the other can effectively balance the mitigation effect on the volume expansion of active materials, especially silicon-based anode materials, and electrolyte wettability.

[0079] In some embodiments, the interfacial area ratio Sdr of the copper foil is 0.6 to 1.3. For example, the interfacial area ratio Sdr of the copper foil can be 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, or within any range of the above values. This configuration allows the copper foil to possess higher electrolyte wetting ability and active material loading capacity.

[0080] In some embodiments, the surface roughness Ra of the copper foil is 0.18 μm to 0.40 μm, and Rz is 1.0 μm to 1.3 μm. This setting is beneficial for balancing the adhesion of the active layer and the long-term stability of the battery. For example, Ra can be 0.18 μm, 0.20 μm, 0.21 μm, 0.22 μm, 0.23 μm, 0.24 μm, 0.25 μm, 0.28 μm, 0.30 μm, 0.32 μm, 0.34 μm, 0.36 μm, 0.38 μm, 0.40 μm, or any range thereof; Rz can be 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, or any range thereof. This setting is beneficial for achieving a balance between high specific surface area and good mechanical strength of the copper foil.

[0081] It is understood that in this application, surface roughness "Rz" refers to the average peak-to-valley height, which is the average of the vertical distances between multiple highest and lowest peaks within a sampling length. Its testing standard can be found in GB / T29847-2013. Surface roughness "Ra" refers to the arithmetic mean of the absolute values ​​of the deviations of all points from its average line within a sampling length. Its testing standard can be found in JIS B 0601.

[0082] In this application, "interface expansion area ratio" refers to a parameter, measured according to ISO 25178-2:2021, that indicates how much the expanded area (surface area) of a defined region increases relative to the area of ​​the defined region. In this application, the interface expansion area ratio is expressed as the increase in surface area (%). A smaller value indicates a surface shape closer to a flat surface; the interface expansion area ratio for a completely flat surface is 0%. Conversely, a larger value indicates a surface shape closer to a surface with more irregularities. For example, an interface expansion area ratio of 20% indicates that the surface area has increased by 20% from a completely flat surface.

[0083] In some embodiments, the content of other metallic elements in the copper foil is ≤0.1 mg / m³. 2 The other metallic elements include one or more of zinc, tin, manganese, zirconium, and aluminum. This reduces or even eliminates the potential for electrochemical side reactions when copper foil is used as a current collector.

[0084] Non-limiting, the content of other metallic elements in copper foil can be obtained by inductively coupled plasma emission spectroscopy (ICP).

[0085] Secondly, this application provides a method for preparing copper foil, which can be used to prepare the copper foil of the first aspect of this application, and may specifically include the following steps:

[0086] S1. Provide copper foil substrate 1;

[0087] S2. Construct a precursor layer on at least one side surface of the copper foil substrate 1. The precursor layer comprises a copper alloy, which includes copper and a removable metal element. The removable metal element includes one or more of zinc, tin, manganese, zirconium, and aluminum.

[0088] S3. The precursor layer is subjected to dealloying treatment to remove removable metal elements in the precursor layer, and a porous copper layer 2 containing multiple channels 20 is prepared. At least some of the channels 20 are interconnected and form a three-dimensional network structure. The average pore size of the channels 20 is 40nm~200nm.

[0089] In the above preparation method, step S2 constructs a copper alloy precursor layer, and then step S3 performs a dealloying treatment on the precursor layer to remove the removable metal elements in the precursor layer and retain the copper. During the dealloying process, multiple channels 20 can be formed, and at least some of the channels 20 will be interconnected to form a three-dimensional network structure, which can eventually form a porous copper layer 2.

[0090] It is understood that at least one of the parameters such as morphology, average pore diameter, depth, porosity, and distribution density of the channel 20 formed by the above preparation method will affect the surface roughness and interface expansion area ratio Sdr of the copper foil; that is, when these parameters change, the surface roughness and interface expansion area ratio Sdr of the copper foil will change.

[0091] In some embodiments, the content of removable metal elements in the precursor layer is 50 mg / m³. 2 ~220mg / m 2 For example, the content of removable metal elements in the precursor layer can be 50 mg / m³. 2 80mg / m 2 100mg / m 2 120mg / m 2 140mg / m 2 160mg / m 2 180mg / m 2 200mg / m 2 220mg / m 2 Or within any of the above values. The content of removable metal elements in the precursor can directly determine the nucleation site density and etching depth after dealloying, thereby enabling the control of parameters of the channel 20 (such as average pore size, depth, porosity, etc.); based on this, by reasonably controlling the content of removable metal elements within the above range, the average pore size, depth, porosity, and other parameters of the channel 20 can be controlled to the range described above in this application.

[0092] In some embodiments, a precursor layer is constructed on both sides of the copper foil substrate 1, wherein the precursor layer on one side is a first precursor layer and the precursor layer on the other side is a second precursor layer, and the content of removable metal elements in the first precursor layer is greater than the content of removable metal elements in the second precursor layer.

[0093] Furthermore, the content of removable metal elements in the first precursor layer is 50 mg / m³. 2 ~220mg / m 2 The content of removable metal elements in the second precursor layer is 100 mg / m³. 2 ~130mg / m 2.

[0094] For example, the content of removable metal elements in the first precursor layer can be 50 mg / m³. 2 80mg / m 2 100mg / m 2 120mg / m 2 150mg / m 2 160mg / m 2 170mg / m 2 180mg / m 2 190mg / m 2 200mg / m 2 220mg / m 2 Or within any of the above values; the content of removable metal elements in the second precursor layer can be 100 mg / m³. 2 110mg / m 2 120mg / m 2 130mg / m 2 Or it may fall within the range of any of the above values.

[0095] By constructing a first precursor layer and a second precursor layer, and independently controlling the parameters (such as composition and content, thickness, etc.) of the first and second precursor layers, followed by alkaline and acid treatments respectively, a double-sided heterogeneous structure with different pore parameters (such as average pore size, depth, porosity, etc.) can be constructed on the copper foil substrate 1. Furthermore, by rationally controlling the content of removable metal elements in the first precursor layer, the parameters (such as average pore size, depth, porosity, etc.) of the pores 20 in the first porous copper layer 21 can be controlled and adjusted to the range of parameters described above for the first porous copper layer 21; similarly, by rationally controlling the content of removable metal elements in the second precursor layer, the parameters (such as average pore size, depth, porosity, etc.) of the pores 20 in the second porous copper layer 22 can be controlled and adjusted to the range of parameters described above for the second porous copper layer 22.

[0096] Therefore, this application, through its unique process route of "independent construction of precursor layers on both sides (i.e., both surfaces of the copper foil substrate 1) + dealloying," can independently adjust the alloy composition, thickness, and subsequent dealloying parameters on both sides. This allows for complete decoupling and customized design of the parameters of the porous copper layer 2 on both sides of the final product (such as pore size distribution, porosity, pore morphology, and effective thickness), meeting the differentiated requirements of different electrode interfaces (such as negative electrode SEI film construction and positive electrode interface modification) on the current collector surface. This overcomes the limitations of traditional dealloying technology in differentiating the two sides of the foil.

[0097] In some embodiments, the removable metal element includes one or more of zinc, tin, manganese, zirconium, and aluminum, with zinc being a possible choice. This facilitates the removal of the removable metal element through alkaline and acid treatments, achieving a more complete dealloying process.

[0098] In some embodiments, step S2, which involves constructing a precursor layer on at least one side surface of the copper foil substrate 1, includes: constructing the precursor layer on at least one side surface of the copper foil substrate 1 by electroplating.

[0099] This preparation method can construct a precursor layer based on an electroplating process, and then construct a porous copper layer 2 based on a dealloying process, thus eliminating the need for expensive vacuum equipment or complex nanoimprinting steps. This process can be seamlessly integrated with existing copper foil production lines, offering advantages such as a short process flow, high controllability, high batch stability, and ease of large-scale continuous production. It provides a practical and feasible technical solution for the low-cost manufacturing of next-generation high-performance lithium-ion battery current collectors.

[0100] In some embodiments, the electroplating solution comprises a copper source and a removable metal source; further, the copper source includes one or more of copper sulfate (CuSO4·5H2O), copper chloride (CuCl2), copper pyrophosphate, and copper methanesulfonate; the removable metal source includes one or more of zinc, tin, manganese, zirconium, and aluminum, and may be a zinc source. Even further, the zinc source includes one or more of zinc sulfate (ZnSO4·7H2O), zinc chloride (ZnCl2), zinc oxide, and zinc methanesulfonate.

[0101] In some embodiments, the molar ratio of copper source to removable metal source is (0.5~6):1. For example, this molar ratio can be 0.5:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, or any range of the above values. By reasonably controlling the molar ratio of copper source to removable metal source, the composition of the precursor layer (i.e., the content of removable metal elements in the precursor layer) can be controlled, thereby controlling the porosity of the dealloyed porous copper layer 2 and the average pore size of the channels 20.

[0102] In some embodiments, the concentration of the copper source is 0.1 mol / L to 0.3 mol / L. For example, the concentration of the copper source can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, or within any range of the above values.

[0103] In some embodiments, the concentration of the removable metal source is 0.05 mol / L to 0.2 mol / L. For example, the concentration of the removable metal source can be 0.05 mol / L, 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, or within any range of the above values.

[0104] In some embodiments, the pH value of the electroplating solution is 10 to 13. For example, the pH value can be 10, 11, 12, 13, or any range thereof. This allows the ions capable of removing metal elements to exist in a stable complexed state in the electroplating solution.

[0105] In some implementations, the electroplating current density is 0.1 A / dm². 2 ~10A / dm 2 0.5A / dm is optional. 2 ~5A / dm 2 For example, the current density can be 0.1 A / dm³. 2 0.5A / dm 2 0.8A / dm 2 1A / dm 2 3A / dm 2 5A / dm 2 7A / dm 2 9A / dm 2 10A / dm 2 Or it may fall within any of the above values. By adjusting the current density, the deposition rate and grain nucleation density can be controlled, and the amount of removable metal elements deposited in the precursor layer can be adjusted.

[0106] In some embodiments, the electroplating time is 20s to 240s. For example, the electroplating time can be 20s, 60s, 100s, 150s, 200s, 240s, or any range of the above values.

[0107] In some embodiments, the mechanical stirring speed is 40 rpm to 120 rpm, which is beneficial for promoting mass transfer and eliminating concentration polarization. In other embodiments, the electrode spacing between the cathode and anode during electroplating is 20 mm to 60 mm, which is beneficial for ensuring a uniform electric field distribution.

[0108] In some embodiments, the electroplating solution also includes one or more of a complexing agent, a leveling agent, and a pH adjuster.

[0109] In some embodiments, the complexing agent includes one or more of sodium citrate, disodium ethylenediaminetetraacetate, glycine, sodium potassium tartrate, triethanolamine, and potassium pyrophosphate. These complexing agents can stabilize metal ions in the electroplating solution, inhibit the free hydrolysis of metal ions, adjust the cathode polarization, promote the co-deposition of copper and removable metal elements, and make the alloy composition in the precursor layer more uniform.

[0110] Furthermore, the complexing agents include sodium citrate and glycine. The combination of sodium citrate and glycine can effectively broaden the electroplating current density window, reducing or even avoiding scorching in high-current areas and insufficient deposition in low-current areas.

[0111] In some embodiments, the concentration of the complexing agent is 1 g / L to 50 g / L. For example, the concentration of the complexing agent can be 1 g / L, 5 g / L, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, or any of the above ranges.

[0112] In some embodiments, the leveling agent includes one or more of xylitol, polyethylene glycol, gelatin, guar gum, hydroxyethyl cellulose, polyethyleneimine, and thiourea derivatives. Further, the polyethylene glycol has a molecular weight of 200-20000. These leveling agents can be adsorbed onto the cathode surface, inhibiting excessively rapid grain growth, reducing or even eliminating internal stress in the precursor layer, and promoting the uniform nanoscale dispersion of removable metal elements, which is beneficial for promoting the formation of a uniform three-dimensional porous structure in the precursor layer.

[0113] Furthermore, the leveling agent includes xylitol and guar gum. Xylitol, as a nonionic complexing agent, can further refine the crystal nuclei; guar gum, as a polymer inhibitor, can significantly improve the leveling properties of the precursor layer; the synergistic effect of the two can reduce or even avoid large pores or structural collapse after dealloying, and promote the formation of the small-diameter, narrow-distribution pores 20 described above in this application.

[0114] Furthermore, the mass ratio of guar gum to xylitol is (5~80):1. For example, this mass ratio can be 5:1, 10:1, 20:1, 30:1, 35:1, 40:1, 45:1, 50:1, 55:1, 60:1, 70:1, 80:1, or any range of the above values. Reasonably controlling the mass ratio of xylitol to guar gum is beneficial to enhancing their synergistic effect, thereby further promoting the formation of the small-particle-size, narrow-distribution pores 20 described above. By adjusting this mass ratio, the parameters of the pores 20 in the porous copper layer 2 (such as average pore size, depth, porosity, etc.) can be controlled.

[0115] In some embodiments, the concentration of the leveling agent is 1 g / L to 100 g / L. For example, the concentration of the leveling agent can be 1 g / L, 5 g / L, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, or any of the above ranges.

[0116] In some embodiments, the pH adjuster includes one or more of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrochloric acid, and boric acid; sodium hydroxide is optional. These pH adjusters help maintain the acid-base balance of the electroplating solution, provide the necessary solution conductivity, and ensure uniform current distribution.

[0117] In some embodiments, the concentration of the pH adjuster is 20 g / L to 150 g / L. For example, the concentration of the leveling agent can be 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L, 150 g / L, or any of the above ranges.

[0118] In some embodiments, the dealloying process includes sequential alkaline and acid treatments. Alkaline treatment combined with acid treatment facilitates more complete removal of removable metal elements from the precursor layer, resulting in very low concentrations (e.g., ≤0.1 mg / m³) in the final product. 2 This is to reduce or even avoid the potential risks of electrochemical side reactions when copper foil is used as a current collector.

[0119] In some embodiments, the alkaline treatment includes immersing the precursor layer in an alkaline solution for 1 to 15 hours. Further, the alkaline solution includes one or more of NaOH, KOH, NaHCO3, and NH3·H2O.

[0120] In some embodiments, the alkaline solution contains 5wt% to 10wt% NaOH, 5wt% to 10wt% KOH, 10wt% to 20wt% NaHCO3, and 2wt% to 4wt% NH3·H2O.

[0121] In some embodiments, the acid treatment includes immersing the alkali-treated precursor layer in an acidic solution for 1 to 60 minutes. Further, the acidic solution includes one or both hydrochloric acid and sulfuric acid. This ensures the thorough removal of removable metal elements and other compounds.

[0122] In some embodiments, the concentration of hydrochloric acid in the acidic solution is 2 mol / L to 4 mol / L, the concentration of sulfuric acid is 2 mol / L to 4 mol / L, and the volume ratio of hydrochloric acid to sulfuric acid is (1 to 2):1.

[0123] In some embodiments, before step S2, a pretreatment step of the copper foil substrate 1 may be included, including rinsing the copper foil substrate 1 with 10wt%~15wt% hydrochloric acid to wash away the oxide layer on the surface of the copper foil and expose a shiny metal surface.

[0124] Thirdly, this application provides an electrode sheet, including a current collector and an active layer disposed on at least one side of the current collector, wherein the current collector includes a copper foil as described in the first aspect or a copper foil prepared by the preparation method described in the second aspect.

[0125] In some embodiments, the active material in the active layer includes a silicon-based material; optionally, the silicon-based material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Silicon-based materials exhibit significant volume expansion during cycling. Using them in conjunction with the copper foil of this application can effectively mitigate this volume expansion during charge and discharge, reduce electrode pulverization and detachment, and improve the battery's cycle life.

[0126] Fourthly, this application provides a secondary battery including third-party electrode plates. Further, the electrode plates include either a positive electrode plate or a negative electrode plate.

[0127] In some embodiments, the secondary battery also includes an electrolyte and a separator. During the charging and discharging process, ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0128] Fifthly, this application provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0129] In some implementations, the type of electrical equipment is not particularly limited, and it can be any electronic device known in the prior art. For example, the electrical equipment may include, but is not limited to, power tools, electric vehicles, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, etc.

[0130] The following are specific embodiments, which describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations within the scope of the disclosure of this application will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0131] Example 1

[0132] (1) Take a copper foil substrate with a thickness of 3.8 μm, clean the oxide layer with 8 wt% hydrochloric acid and wash with water to expose the metallic luster.

[0133] (2) Using the treated copper foil substrate as the cathode and an iridium-plated titanium plate as the anode, electroplating was performed on the smooth surface of the copper foil (S-surface, roughness Ra of 0.19 μm, Rz of 1.12 μm, and the interfacial extension area ratio Sdr of the copper foil of 66%) to form a precursor layer. The zinc content in the precursor layer was 118 mg / m³. 2 The precursor layer has a thickness of 165 nm, and its EDX mapping can be found in [reference needed]. Figure 3 .

[0134] Electroplating solution formula: 0.18 mol / L CuSO4·5H2O, 0.06 mol / L ZnSO4·5H2O (molar ratio of copper source to zinc source is 3:1), 0.4 g / L xylitol, 2 g / L guar gum, and 45 g / L sodium citrate, 2 g / L glycine, 2 g / L gelatin, 2 g / L polyethylene glycol (weight average molecular weight is 6000), 100 g / L sodium hydroxide, with a pH value of 12.

[0135] Electroplating process parameters: mechanical stirring speed is 50 rpm, distance between cathode and anode plates is 40 mm, current density is 1.5 A / dm², and electroplating time is 30 s.

[0136] (3) The precursor layer is subjected to dealloying treatment, specifically: the precursor layer is pre-etched by immersing it in an alkaline solution for 12 hours, the alkaline aqueous solution containing 5wt% NaOH + 2wt% NH3·H2O; then it is completely removed by immersing it in an acidic solution for 10 minutes to form a porous copper layer (150nm thick), thus obtaining copper foil. The acidic solution contains 3 mol / L HCl + 2 mol / L H2SO4, with a volume ratio of 1:1. See the EDX mapping and SEM images of the copper foil. Figure 4 and Figure 6 .

[0137] Example 2

[0138] The preparation method is similar to that in Example 1, the main difference being that xylitol and guar gum are omitted from the plating solution formulation. The SEM image of the resulting copper foil is shown below. Figure 6 .

[0139] Example 3

[0140] The preparation method is similar to that in Example 1, the main difference being that xylitol is omitted from the plating solution formulation. The EDX mapping and SEM images of the resulting copper foil are shown below. Figure 5 .

[0141] Example 4

[0142] The preparation method is similar to that in Example 1, the main difference being that guar gum is omitted from the plating solution formulation.

[0143] Example 5

[0144] The preparation method is similar to that of Example 1, the main difference being that the concentration of ZnSO4·5H2O in the electroplating solution was increased from 0.06 mol / L to 0.12 mol / L. The zinc content in the precursor layer was 165 mg / m³. 2 The SEM image of the obtained copper foil can be found in [reference needed]. Figure 6 .

[0145] Example 6

[0146] The preparation method is similar to that of Example 1, with the main difference being that the concentration of ZnSO4·5H2O in the electroplating solution was increased from 0.06 mol / L to 0.12 mol / L, and the electroplating time was changed from 30 s to 50 s. The zinc content in the precursor layer was 218 mg / m³. 2 .

[0147] Example 7

[0148] Similar to the preparation method in Example 1, the main difference is that in step (2), the treatment of the smooth surface is changed to the treatment of the rough surface (M surface, roughness Ra is 0.18 μm, Rz is 1.09 μm, and the interface expansion area ratio Sdr of the copper foil is 66%). The treatment process is the same as in Example 1. The SEM image of the obtained copper foil can be found in [reference needed]. Figure 6 .

[0149] Example 8

[0150] Similar to the preparation method of Example 1, the main difference is that in step (2), after the smooth surface is treated, the rough surface is treated. The process of treating the smooth surface is the same as in Example 1, and the process of treating the rough surface is the same as in Example 7. Other steps are unchanged.

[0151] Comparative Example 1

[0152] Similar to the preparation method in Example 1, the main difference is that the electroplating time is changed from 30s to 10s, and the average pore size of the porous copper layer is 24nm.

[0153] Comparative Example 2

[0154] Similar to the preparation method in Example 1, the main difference is that the electroplating time is changed from 30s to 90s, and the average pore size of the porous copper layer is 216nm.

[0155] The copper foils prepared in the examples and comparative examples were subjected to relevant performance tests, and the test results are shown in Tables 1 and 2 below. In Table 1, the S-side refers to the porous copper layer connected to the smooth side of the copper foil, and the M-side refers to the porous copper layer connected to the rough side of the copper foil.

[0156] The test conditions or standards for each performance test item are as follows:

[0157] (1) The morphology, roughness, interface expansion area ratio and pore parameters of the copper foils prepared in different embodiments were tested and characterized using a Zeiss field emission scanning electron microscope (SEM), an X-ray energy dispersive spectrometer (EDX Mapping) and a 3D laser measurement microscope.

[0158] (2) The elemental content was detected using an inductively coupled plasma atomic emission spectrometer (ICP).

[0159] (3) Use a super depth-of-field microscope to detect porosity.

[0160] (4) Use mercury porosimetry to test the wettability of the electrolyte and test the pore volume that the electrolyte can enter (see GB / T21650.1); wherein the electrolyte is composed of: dissolving LiPF6 in ethylene carbonate (EC) to prepare an electrolyte of 1 mol / L.

[0161] Table 1

[0162]

[0163] Table 2

[0164]

[0165] A comparison of Examples 1-8 with Comparative Examples 1-2 shows that the copper foil of this application can effectively balance the tensile strength and elongation of the copper foil by reasonably controlling the average pore size of the channels; on this basis, it can also effectively balance the wettability of the electrolyte.

[0166] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0167] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A copper foil, characterized in that, It includes a copper foil substrate and a porous copper layer disposed on at least one surface of the copper foil substrate. The porous copper layer contains a plurality of channels, at least some of which are interconnected to form a three-dimensional network structure. The average pore size of the channels is 40 nm to 200 nm.

2. The copper foil according to claim 1, characterized in that, The porous copper layer is provided on both sides of the copper foil substrate. The porous copper layer on one side is a first porous copper layer, and the porous copper layer on the other side is a second porous copper layer. The average pore diameter of the pores in the first porous copper layer is greater than the average pore diameter of the pores in the second porous copper layer, and the porosity of the first porous copper layer is greater than the porosity of the second porous copper layer.

3. The copper foil according to claim 2, characterized in that, One or more of the following conditions must be met: (1) The ratio of the average pore diameter of the channels in the first porous copper layer to the average pore diameter of the channels in the second porous copper layer is (1.2~4):1; (2) The average pore size of the channels in the first porous copper layer is 30nm~180nm, and the average pore size of the channels in the second porous copper layer is 40nm~60nm; (3) The porosity of the first porous copper layer is 5%~20%, and the porosity of the second porous copper layer is 5%~15%.

4. The copper foil according to claim 1 or 2, characterized in that, One or more of the following conditions must be met: (1) The depth of the channel is 10nm~300nm; (2) The thickness of the porous copper layer is 100nm~350nm; (3) The interface expansion area ratio Sdr of the copper foil is 0.6~1.3; (4) The surface roughness Ra of the copper foil is 0.18μm~0.40μm, and Rz is 1.0μm~1.3μm; (5) The content of other metallic elements in the copper foil is ≤0.1mg / m 2 The other metallic elements include one or more of zinc, tin, manganese, zirconium, and aluminum.

5. A method for preparing copper foil, characterized in that, include: Provide copper foil substrate; A precursor layer is constructed on at least one surface of the copper foil substrate. The precursor layer comprises a copper alloy, which includes copper and a removable metal element, wherein the removable metal element includes one or more of zinc, tin, manganese, zirconium, and aluminum. The precursor layer is subjected to a dealloying process to remove the removable metal element from the precursor layer, thereby preparing a porous copper layer containing multiple channels. At least some of the channels are interconnected to form a three-dimensional network structure, and the average pore size of the channels is 40nm~200nm.

6. The preparation method according to claim 5, characterized in that, One or more of the following conditions must be met: (1) The content of the removable metal element in the precursor layer is 50 mg / m³. 2 ~220mg / m 2 ; Optionally, the precursor layer is constructed on both sides of the copper foil substrate, wherein the precursor layer on one side is a first precursor layer and the precursor layer on the other side is a second precursor layer, and the content of the removable metal element in the first precursor layer is greater than the content of the removable metal element in the second precursor layer. Optionally, the content of the removable metal element in the first precursor layer is 50 mg / m³. 2 ~220mg / m 2 The content of the removable metal element in the second precursor layer is 100 mg / m³. 2 ~130mg / m 2 ; (2) The removable metal element is zinc.

7. The preparation method according to claim 5 or 6, characterized in that, The step of constructing a precursor layer on at least one surface of the copper foil substrate includes: The precursor layer is constructed on at least one surface of the copper foil substrate by electroplating. Optionally, the electroplating solution includes a copper source and a removable metal source; Alternatively, the molar ratio of the copper source to the removable metal source is (0.5~6):1; Alternatively, the concentration of the copper source is 0.1 mol / L to 0.3 mol / L; Alternatively, the concentration of the removable metal source is 0.05 mol / L to 0.2 mol / L; Optionally, the pH value of the electroplating solution is 10-13; Optionally, the current density of the electroplating is 0.1 A / dm³. 2 ~10A / dm 2 0.5A / dm is optional. 2 ~5A / dm 2 ; Optionally, the electroplating time is 20s to 240s.

8. The preparation method according to claim 7, characterized in that, The electroplating solution also contains one or more of a complexing agent, a leveling agent, and a pH adjuster; Optionally, the complexing agent includes one or more of sodium citrate, disodium EDTA, glycine, sodium potassium tartrate, triethanolamine, and potassium pyrophosphate; optionally, it includes sodium citrate and glycine. Optionally, the concentration of the complexing agent is 1 g / L to 50 g / L; Optionally, the leveling agent includes one or more of xylitol, polyethylene glycol, gelatin, guar gum, hydroxyethyl cellulose, polyethyleneimine, and thiourea derivatives; More preferably, the leveling agent comprises xylitol and guar gum; more preferably, the mass ratio of guar gum to xylitol is (5~80):1; Optionally, the concentration of the leveling agent is 1 g / L to 100 g / L; Optionally, the pH adjuster includes one or more of sodium hydroxide, potassium hydroxide, sulfuric acid, hydrochloric acid, and boric acid; Sodium hydroxide can be used as an alternative. Optionally, the concentration of the pH adjuster is 20 g / L to 150 g / L.

9. The preparation method according to claim 5 or 6, characterized in that, The dealloying process includes sequential alkaline and acid treatments, satisfying one or more of the following conditions: (1) The alkaline treatment includes: soaking the precursor layer in an alkaline solution for 1 h to 15 h; Optionally, the alkaline solution includes one or more of NaOH, KOH, NaHCO3, and NH3·H2O; Alternatively, in the alkaline solution, the mass content of NaOH is 5wt%~10wt%, the mass content of KOH is 5wt%~10wt%, the mass content of NaHCO3 is 10wt%~20wt%, and the mass content of NH3·H2O is 2wt%~4wt%. (2) The acid treatment includes: immersing the precursor layer after the alkali treatment in an acidic solution for 1 min to 60 min; Optionally, the acidic solution includes one or both of hydrochloric acid and sulfuric acid; Alternatively, the concentration of the hydrochloric acid is 2 mol / L to 4 mol / L, the concentration of the sulfuric acid is 2 mol / L to 4 mol / L, and the volume ratio of the hydrochloric acid to the sulfuric acid is (1 to 2):

1.

10. An electrode sheet, characterized in that, It includes a current collector and an active layer disposed on at least one side of the current collector, wherein the current collector includes the copper foil according to any one of claims 1 to 4 or the copper foil prepared by the preparation method according to any one of claims 5 to 9.

11. The electrode according to claim 10, characterized in that, The active material in the active layer includes a silicon-based material; optionally, the silicon-based material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys.

12. A secondary battery, characterized in that, Includes the electrode as described in claim 10 or 11.

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