Composite current collector, method for manufacturing the same, negative electrode sheet, and secondary battery

Abstract

This application provides a composite current collector and its preparation method, a negative electrode, and a secondary battery. The composite current collector includes a substrate layer, a transition layer disposed on at least one side of the substrate layer, and a conductive layer disposed on the transition layer. The substrate layer is made of one or more of copper-nickel alloy, copper-tin alloy, and iron-nickel alloy. The elements contained in the transition layer are not entirely the same as those contained in the substrate layer. An elemental gradient diffusion region exists at the interface between the substrate layer and the transition layer. Within this region, the elements contained in the substrate layer and the transition layer diffuse into each other, and their concentrations are distributed in a gradient along the thickness direction. The composite current collector provided by this application has improved interfacial bonding.

Description

Technical Field

[0001] This application relates to the field of electrochemical technology, and in particular to composite current collectors and their preparation methods, negative electrode sheets, and secondary batteries. Background Technology

[0002] As a key load-bearing and conductive component inside the battery, the performance of the current collector is crucial. Currently, in pursuit of higher energy density, alloy composite current collectors with high mechanical strength are often used. However, the interfacial bonding force of traditional alloy composite current collectors is unstable, leading to poor cycle performance of the battery. Summary of the Invention

[0003] Based on this, this application provides a composite current collector and its preparation method, a negative electrode sheet and a secondary battery, aiming to improve the interfacial bonding force of the alloy composite current collector, thereby improving the cycle performance of the battery.

[0004] A first aspect of this application provides a composite current collector, comprising: a substrate layer, a transition layer disposed on at least one side of the substrate layer, and a conductive layer disposed on the transition layer;

[0005] The material of the base layer includes one or more of copper-nickel alloy, copper-tin alloy and iron-nickel alloy, and the elements contained in the transition layer are not exactly the same as those contained in the base layer;

[0006] At the interface where the matrix layer and the transition layer are in contact, there is an element gradient diffusion region. Within the element gradient diffusion region, the elements contained in the matrix layer and the elements contained in the transition layer diffuse into each other and their concentrations are distributed in a gradient along the thickness direction.

[0007] In some embodiments, the gradient distribution satisfies the following: along the thickness direction, the elemental gradient diffusion region gradually decreases in atomic percentage concentration of the elements contained in the matrix layer from the side relatively close to the matrix layer to the side relatively close to the transition layer, and gradually increases in atomic percentage concentration of the elements contained in the transition layer.

[0008] In some embodiments, the thickness of the elemental gradient diffusion region is 10 nm to 50 nm, and can be selected as 30 nm to 50 nm.

[0009] In some implementations, one or more of the following conditions are met:

[0010] (1) The surface roughness Ra of the substrate layer is 0.05μm~0.20μm, and Rz is 0.23μm~1.15μm;

[0011] (2) The thickness of the oxide layer on the surface of the substrate layer is ≤5nm;

[0012] (3) The material of the transition layer includes one or more of nickel, copper, cobalt and cobalt alloys;

[0013] (4) The thickness of the transition layer is 0.1μm~0.5μm.

[0014] In some implementations, one or more of the following conditions are met:

[0015] (1) The thickness of the substrate layer is 5μm~20μm;

[0016] (2) The thickness of the substrate layer is 70% to 95% of the total thickness of the composite current collector;

[0017] (3) The material of the conductive layer includes one or more of copper, silver, gold and zinc, and the types of elements contained in the conductive layer are different from those contained in the transition layer;

[0018] (4) The thickness of the conductive layer is 0.1μm~2μm.

[0019] In some implementations, one or more of the following conditions are met:

[0020] (1) The tensile strength of the composite current collector is ≥1000MPa;

[0021] (2) The volume resistivity of the composite current collector is ≤3.5 μΩ·cm.

[0022] A third aspect of this application provides a method for preparing a composite current collector, comprising:

[0023] The surface of the alloy substrate is activated by an acidic reagent containing an oxidant, or by an electrochemical anodic oxidation method, to obtain a substrate layer. The material of the substrate layer includes one or more of copper-nickel alloy, copper-tin alloy, and iron-nickel alloy. The activation treatment time is 5s to 20s.

[0024] A transition layer with a different element type than that contained in the substrate layer is electrodeposited on at least one side of the substrate layer, so that an element gradient diffusion region is formed at the interface where the substrate layer and the transition layer are in contact. Within the element gradient diffusion region, the elements contained in the substrate layer and the elements contained in the transition layer diffuse into each other and the concentration is distributed in a gradient along the thickness direction.

[0025] A conductive layer is prepared on the transition layer to prepare a composite current collector.

[0026] In some implementations, one or more of the following conditions are met:

[0027] (1) The pH value of the acidic reagent is 1~4.5, and can be selected as 2.5~4.5;

[0028] (2) The oxidizing agent includes hydrogen peroxide and / or ammonium persulfate;

[0029] (3) The mass concentration of the oxidant in the acidic reagent is 0.3% to 5%.

[0030] In some implementations, one or more of the following conditions are met:

[0031] (1) The surface roughness Ra of the substrate layer is 0.05μm~0.20μm, and Rz is 0.23μm~1.15μm;

[0032] (2) The thickness of the oxide layer on the surface of the substrate layer is ≤5nm.

[0033] A third aspect of this application provides a negative electrode sheet, including the composite current collector of the first aspect of this application or the composite current collector prepared by the preparation method of the second aspect of this application.

[0034] A fourth aspect of this application provides a secondary battery, including the negative electrode sheet of the third aspect of this application.

[0035] The above technical solutions provided in this application can effectively prevent the diffusion of matrix elements into the conductive layer by setting a transition layer between the matrix layer and the conductive layer, and can also realize the metallurgical bonding transition and stress buffer between the matrix layer and the conductive layer; the element gradient diffusion region therein is conducive to improving the interfacial bonding stability of the composite current collector, thereby improving the cycle stability of the battery. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a composite current collector according to an embodiment of this application.

[0037] Figure 2 The image shows the cross-sectional energy spectrum (EDS) of the matrix layer and transition layer of the composite current collector in Example 1.

[0038] Figure reference numerals: 11 substrate layer; 12 transition layer; 13 conductive layer. Detailed Implementation

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] Currently, to achieve high energy density, alloy-type composite current collectors (such as alloy substrate + conductive coating) are commonly used in batteries. However, research has revealed the following problems with current alloy-type composite current collectors: ① Unstable interfacial bonding: The layers of the current collector rely heavily on physical adsorption or ordinary chemical bonding. Under long-term charge-discharge volume expansion stress, microcracks at the interface are prone to propagate or even peel off, leading to unstable interfacial bonding and increased contact resistance. ② Thermal expansion mismatch: There are differences in the coefficients of thermal expansion between adjacent layers in the current collector (i.e., thermal expansion coefficient mismatch). During the temperature change cycles generated by battery charge-discharge, the stress caused by the thermal expansion coefficient mismatch cannot be effectively buffered, easily generating thermal stress that leads to interfacial cracking, further deteriorating the interfacial bonding and contact resistance. All of these factors contribute to a decrease in battery cycle stability. In view of this, the inventors have proposed the following technical solution in this application.

[0046] Firstly, this application provides a composite current collector, see [link to application]. Figure 1 It includes: a substrate layer 11, a transition layer 12 disposed on at least one side of the substrate layer, and a conductive layer 13 disposed on the transition layer 12;

[0047] The material of the substrate layer 11 includes one or more of copper-nickel alloy, copper-tin alloy and iron-nickel alloy, and the elements contained in the transition layer 12 are not exactly the same as those contained in the substrate layer 11.

[0048] At the interface where the matrix layer 11 and the transition layer 12 are in contact, there is an element gradient diffusion region. Within the element gradient diffusion region, the elements contained in the matrix layer 11 and the elements contained in the transition layer 12 diffuse into each other and their concentrations are distributed in a gradient along the thickness direction.

[0049] It should be noted that the thickness direction in this application refers to the thickness direction of the substrate layer or the thickness direction of the transition layer, that is, the thickness direction of the composite current collector.

[0050] It is understood that "the types of elements are not completely the same" in this application means that the types of elements can be partially the same, partially different, or completely different. As an example, if the base layer contains a copper-nickel alloy, then the transition layer can contain nickel, copper, or other non-nickel and non-copper elements, but cannot be a copper-nickel alloy like the base layer.

[0051] The technical solution provided in this application, by setting a transition layer between the substrate layer and the conductive layer, can not only effectively prevent the diffusion of substrate elements into the conductive layer, but also achieve metallurgical bonding transition and stress buffering between the substrate layer and the conductive layer. On the one hand, the elements in the element gradient diffusion region diffuse into each other and are distributed in a gradient, which can achieve metallurgical bonding and enhance the metallurgical bonding effect. This makes the interfacial bonding force significantly better than physical adsorption or ordinary chemical bonding, which is beneficial to improving interfacial bonding stability and reducing contact resistance. On the other hand, the element gradient diffusion region can reduce the stress concentration points caused by the difference in thermal expansion coefficients between layers with different element types, effectively alleviate the interfacial stress caused by thermal expansion mismatch, and reduce interfacial cracking caused by interfacial stress. Therefore, it is also beneficial to improve the interfacial bonding force and contact resistance. Thus, this element gradient diffusion region is beneficial to improving the interfacial bonding stability of the composite current collector, thereby improving the cycle stability of the battery.

[0052] In some implementations, the gradient distribution satisfies the following: along the thickness direction, the elemental gradient diffusion region gradually decreases in atomic percentage concentration of elements in the matrix layer and gradually increases in atomic percentage concentration of elements in the transition layer from the side relatively closer to the matrix layer to the side relatively closer to the transition layer. This gradient distribution structure without abrupt elemental interface changes can effectively buffer thermal stress and achieve metallurgical bonding between the two layers, thereby improving the interfacial bonding stability of the composite current collector.

[0053] In some embodiments, the thickness of the elemental gradient diffusion region is 10 nm to 50 nm, optionally 30 nm to 50 nm. For example, the thickness can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, or any value within the range above. A suitable thickness of the elemental gradient diffusion region can effectively buffer thermal stress and achieve metallurgical bonding between the two layers, thereby improving the interfacial bonding stability of the composite current collector.

[0054] In some embodiments, the surface roughness Ra of the substrate layer is 0.05 μm to 0.20 μm. For example, the surface roughness Ra of the substrate layer can be 0.05 μm, 0.08 μm, 0.10 μm, 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, 0.20 μm, or within any range of the above values. When the surface roughness Ra of the substrate layer is within the above range, it indicates that the surface of the substrate layer is in a highly active state. This is beneficial for promoting the interdiffusion of elements between the subsequent transition layer and the substrate layer, providing the necessary thermodynamic conditions for the formation of the element gradient diffusion region, thereby forming an element gradient diffusion region within the thickness range of this application at the interface between the transition layer and the substrate layer.

[0055] In some embodiments, the surface roughness Rz of the substrate layer is 0.23 μm to 1.15 μm. For example, the surface roughness Rz of the substrate layer can be 0.23 μm, 0.43 μm, 0.63 μm, 0.83 μm, 1.03 μm, 1.15 μm, or within any range of the above values. When the surface roughness Rz of the substrate layer is within the above range, it indicates that the surface of the substrate layer is in a highly active state. This is beneficial for promoting the interdiffusion of elements between the subsequent transition layer and the substrate layer, providing the necessary thermodynamic conditions for the formation of the element gradient diffusion region, thereby forming an element gradient diffusion region within the thickness range of this application at the interface between the transition layer and the substrate layer.

[0056] It is understood that the surface roughness "Rz" in this application refers to the average peak-valley height, which is the average vertical distance between multiple highest peaks and lowest valleys within a sampling length, and its test standard can refer to GB / T 10610-2009; "Ra" refers to the arithmetic mean of the absolute values ​​of the deviations of all points from its average line within a sampling length, and its test standard can refer to JIS B 0601.

[0057] In some embodiments, the oxide layer thickness on the substrate surface is ≤5 nm. For example, the oxide layer thickness on the substrate surface can be 0, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, or within any range of the above values. Controlling the oxide layer thickness on the substrate surface to below 5 nm allows the substrate surface to be in a high-energy active state, which is beneficial for promoting elemental interdiffusion between the subsequent transition layer and the substrate layer. This provides the necessary thermodynamic conditions for the formation of the elemental gradient diffusion region, thereby forming an elemental gradient diffusion region within the thickness range of this application at the interface between the transition layer and the substrate layer.

[0058] By no means limiting, in this application, the thickness of the oxide layer on the surface of the substrate layer can be measured using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

[0059] In some embodiments, the material of the transition layer includes one or more of nickel, copper, cobalt, and cobalt alloys.

[0060] In some embodiments, the thickness of the transition layer is 0.1 μm to 0.5 μm. For example, the thickness of the transition layer can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or within any range of the above values.

[0061] In some embodiments, the thickness of the substrate layer is 5 μm to 20 μm. For example, the thickness of the substrate layer can be 5 μm, 8 μm, 11 μm, 13 μm, 15 μm, 17 μm, 20 μm, or within any range of these values. In other embodiments, the thickness of the substrate layer is 70% to 95% of the total thickness of the composite current collector.

[0062] In some embodiments, the tensile strength of the matrix layer is ≥800MPa, and can be selected as 800MPa~1000MPa.

[0063] In some embodiments, the conductive layer is made of one or more of copper, silver, gold, and zinc, and the types of elements contained in the conductive layer are different from those contained in the transition layer.

[0064] In some embodiments, the thickness of the conductive layer is 0.1 μm to 2 μm. For example, the thickness of the conductive layer can be 0.1 μm, 0.3 μm, 0.7 μm, 1 μm, 1.3 μm, 1.6 μm, 2 μm, or within any range of the above values.

[0065] In some embodiments, the tensile strength of the composite current collector is ≥1000MPa, and can be selected as 1000MPa~1200MPa. Furthermore, the tensile strength of the composite current collector is increased by 30%~100% compared with the tensile strength of pure copper foil of the same thickness.

[0066] In some embodiments, the volume resistivity of the composite current collector is ≤3.5 μΩ·cm, and can be selected as 2.5 μΩ·cm to 3.5 μΩ·cm. For example, the volume resistivity of the composite current collector can be 0.5 μΩ·cm, 0.8 μΩ·cm, 1 μΩ·cm, 1.5 μΩ·cm, 2 μΩ·cm, 2.5 μΩ·cm, 3 μΩ·cm, 3.5 μΩ·cm, or within any range of the above values.

[0067] It should be noted that the composite current collector provided in this application has ultra-thin applicability. It can still be used under ultra-thin conditions with a thickness of 6μm to 8μm, and there is basically no tearing phenomenon.

[0068] Secondly, this application provides a method for preparing a composite current collector, which can be used to prepare the composite current collector of the first aspect of this application, and may specifically include the following steps:

[0069] S1. The surface of the alloy substrate is activated by an acidic reagent containing an oxidant, or by an electrochemical anodic oxidation method, to obtain a substrate layer. The material of the substrate layer includes one or more of copper-nickel alloy, copper-tin alloy and iron-nickel alloy. The activation treatment time is 5s to 20s.

[0070] S2. Electrodeposit a transition layer on at least one side of the matrix layer that is not exactly the same as the element type contained in the matrix layer, so that an element gradient diffusion zone is formed at the interface where the matrix layer and the transition layer are in contact. Within the element gradient diffusion zone, the elements contained in the matrix layer and the elements contained in the transition layer diffuse into each other and the concentration is distributed in a gradient along the thickness direction.

[0071] S3. Prepare a conductive layer on the transition layer to prepare a composite current collector.

[0072] The aforementioned alloy substrates typically have a relatively thick oxide layer on their surface. This relatively thick oxide layer, combined with the inert surface of the alloy substrate, easily hinders the interdiffusion of elements between the substrate layer and the transition layer. This results in a high surface oxidation barrier that needs to be overcome for interdiffusion, making it difficult to form a metallurgical bond. Therefore, in the above preparation methods, by using an acidic reagent containing an oxidant to activate the surface of the alloy substrate, or by using electrochemical anodizing to activate the surface of the alloy substrate, and controlling the activation time to be 5s~20s, the thickness of the passivation oxide layer on the surface can be reduced and a slightly rough active surface can be formed. This puts the surface of the resulting substrate layer in a highly active state. This highly active state can reduce the surface oxidation barrier that needs to be overcome for interdiffusion between metal atoms, which is beneficial for promoting the interdiffusion of elements between the subsequent transition layer and the substrate layer. This provides the necessary thermodynamic conditions for the formation of an element gradient diffusion zone, thereby forming an element gradient diffusion zone within the thickness range of this application at the interface between the transition layer and the substrate layer, thus forming a metallurgical bond.

[0073] Furthermore, the surface of the alloy substrate can be activated using an acidic reagent containing an oxidant or by electrochemical anodizing. Both methods can rapidly dissolve the original thick passivation oxide layer on the surface of the alloy substrate, thinning the passivation oxide layer and forming a micro-roughened active surface. Furthermore, by adjusting at least one of the following conditions—the composition of the acidic reagent containing the oxidant, the current density of the electrochemical anodizing method, and the activation treatment time—the oxide layer thickness on the substrate surface can be controlled to below 5 nm, and the surface roughness Ra of the substrate layer can be controlled to 0.05 μm–0.20 μm, and Rz to 0.23 μm–1.15 μm.

[0074] In some embodiments, the activation treatment time is 5s to 20s. For example, the activation treatment time can be 5s, 8s, 11s, 13s, 16s, 18s, 20s, or any range of these values. Controlling the activation treatment time within a short window of 5s to 20s is beneficial for controlling the oxide layer thickness on the substrate surface to below 5nm. A shorter time makes it difficult to effectively thin the passivation oxide layer, while a longer time can lead to excessive corrosion of the substrate or the regeneration of a thicker oxide layer. At the same time, controlling the activation treatment time within 5s to 20s also helps to control the surface roughness of the substrate layer within the range required in this application (i.e., Ra is 0.05μm to 0.20μm, Rz is 0.23μm to 1.15μm).

[0075] In some embodiments, the pH value of the acidic reagent is 1 to 4.5, optionally 2.5 to 4.5. This acidic environment helps prevent excessive corrosion of the alloy matrix.

[0076] In some embodiments, the oxidizing agent includes hydrogen peroxide and / or ammonium persulfate.

[0077] In some embodiments, the mass concentration of the oxidant in the acidic reagent is 0.3% to 5%. For example, the mass concentration of the oxidant in the acidic reagent can be 0.3%, 0.7%, 1%, 2%, 3%, 4%, 5%, or within any range of the above values. Controlling this mass concentration is beneficial for promoting the formation of a micro-roughened active surface in the substrate layer and controlling the surface roughness Ra of the substrate layer to 0.05 μm to 0.20 μm and Rz to 0.23 μm to 1.15 μm.

[0078] In some embodiments, the current density of the electrochemical anodic oxidation method is 1 A / dm³. 2 ~3A / dm 2 .

[0079] In some embodiments, the electrolyte in the electrochemical anodic oxidation method includes a sulfuric acid solution with a mass concentration of 10% to 20%.

[0080] In some embodiments, after the activation treatment in step S1, the surface roughness Ra of the resulting substrate layer is 0.05 μm to 0.20 μm, and / or Rz is 0.23 μm to 1.15 μm. When the surface roughness Ra and / or Rz of the substrate layer are within the above range, it indicates that the surface of the substrate layer is in a highly active state. This is beneficial for promoting the interdiffusion of elements between the subsequent transition layer and the substrate layer, providing the necessary thermodynamic conditions for the formation of the element gradient diffusion region, thereby forming an element gradient diffusion region within the thickness range of this application at the interface between the transition layer and the substrate layer.

[0081] In some embodiments, after the activation treatment in step S1, the oxide layer thickness on the surface of the resulting substrate layer is ≤5 nm. Controlling the oxide layer thickness on the surface of the substrate layer to below 5 nm is beneficial for the interdiffusion of elements between the subsequent transition layer and the substrate layer, reduces the high barrier to interdiffusion of elements by the thicker oxide layer, and provides the necessary thermodynamic conditions for the formation of the element gradient diffusion region, thereby forming an element gradient diffusion region within the thickness range of this application at the interface between the transition layer and the substrate layer.

[0082] In some embodiments, the thickness of the surface oxide layer of the alloy substrate is 10 nm to 30 nm. For example, the thickness can be 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, or within any of the above values.

[0083] In some embodiments, the surface roughness of the alloy matrix is ​​Ra' of 0.3 μm to 0.5 μm and Rz' of 2.0 μm to 3.0 μm. For example, Ra' can be 0.3 μm, 0.4 μm, 0.5 μm or within any range of the above values; Rz' can be 2.0 μm, 2.5 μm, 3.0 μm or within any range of the above values.

[0084] The relatively thick oxide layer on the surface of the alloy matrix, combined with the inert surface caused by the roughness mentioned above, easily hinders the interdiffusion of elements between the matrix layer and the transition layer. This results in a high surface oxidation barrier that needs to be overcome for interdiffusion of elements, making it difficult to form metallurgical-grade bonding.

[0085] In some embodiments, the alloy substrate and the conductive layer can be obtained using methods commonly used in the art, such as electrodeposition, rolling, sputtering, etc.; optionally, electrodeposition is used. Electrodepositing a conductive layer on the transition layer allows for a dense bond between the conductive layer and the transition layer, without obvious interface defects.

[0086] It should be noted that the process of preparing the alloy substrate and conductive layer by electrodeposition is a conventional process in this field, and the specific process steps will not be described in detail here.

[0087] Secondly, this application provides a negative electrode sheet, including the composite current collector of the first aspect of this application or the composite current collector prepared by the preparation method of the second aspect of this application.

[0088] Thirdly, this application provides a secondary battery, including the negative electrode sheet of the third aspect of this application.

[0089] In some embodiments, the secondary battery also includes a positive electrode, an electrolyte, and a separator. During battery charging and discharging, active 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 active ions to pass through.

[0090] In some embodiments, the energy density of the secondary battery is ≥300 Wh / kg. The composite current collector of this application has high strength (tensile strength ≥1000MPa), low resistivity (resistivity ≤3.5μΩ·cm) and excellent interfacial stability, and can be used in secondary batteries with energy density ≥300 Wh / kg.

[0091] Fourthly, this application provides an electronic device including the secondary battery of the third aspect of this application.

[0092] In some implementations, the type of electronic device is not particularly limited, and it can be any electronic device known in the prior art. For example, electronic devices may include, but are 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.

[0093] 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.

[0094] Example 1

[0095] 1) Preparation of the alloy matrix: The electrolyte adopts a copper-nickel composite electrolyte system, including 40 g / L copper sulfate, 80 g / L nickel sulfate, 100 g / L sulfuric acid, 0.03 g / L sodium chloride, 60 g / L sodium citrate complexing agent, 2 g / L hydrolyzed collagen (molecular weight 3000 Daltons), 20 ppm sodium thiazolinyl dithiopropane sulfonate, and 100 ppm sodium 2-propene-1-sulfonate. The electrolytic cell temperature is heated to 50℃, stirred evenly, and the electrolytic current density in the electrolytic cell is 4000 A / m. 2 The electroplating time is 30s, and a copper-nickel alloy foil with a thickness of 6μm is generated after the electrochemical reaction.

[0096] 2) Activation Treatment: The surface of the copper-nickel alloy foil was activated using an acidic reagent containing an oxidant to obtain the substrate layer; the activation treatment time was 15 seconds. The acidic reagent was prepared by mixing 5% (w / v) dilute sulfuric acid and 3% (w / v) hydrogen peroxide at a volume ratio of 10:1, with a pH of 2.5. The hydrogen peroxide concentration in the acidic reagent was 0.3%. The surface roughness Ra of the substrate layer obtained after activation treatment was 0.18 μm, and the oxide layer thickness was 2 nm.

[0097] 3) Electroplating of transition layer: Using activated copper-nickel alloy foil as cathode and nickel plate as anode, nickel transition layers with a thickness of 0.2 μm are deposited on both sides of the substrate layer in Watt's nickel plating solution (nickel sulfate 280 g / L, nickel chloride 50 g / L, boric acid 40 g / L, sodium saccharin 1.0 g / L, pH=4.2, temperature 52°C) at a current density of 3 A / dm² for 30 seconds.

[0098] 4) Electroplating of conductive layer: Using a substrate with a nickel transition layer as the cathode, a copper conductive layer with a thickness of 0.5 μm is deposited on both sides of the nickel transition layer in a copper sulfate system plating solution (copper sulfate 90 g / L, concentrated sulfuric acid 110 g / L, sodium chloride 23 mg / L, leveling agent SPS 20 mg / L). The current density is 6 A / dm² and the electroplating time is 60 seconds.

[0099] 5) Post-treatment: Rinse with deionized water and dry to obtain composite current collector.

[0100] Example 2

[0101] Similar to the preparation method in Example 1, the main difference lies in the change of the acidic reagent composition in step 2): 10% (w / w) dilute sulfuric acid and 5 g / L ammonium persulfate are mixed at a volume ratio of 10:1, with a pH of 3. The mass concentration of ammonium persulfate in this acidic reagent is 0.45%. The activation treatment time is 20 s. The surface roughness Ra of the resulting substrate layer after activation treatment is 0.09 μm; the thickness of the surface oxide layer is 4 nm.

[0102] Example 3

[0103] Similar to the preparation method in Example 1, the main difference lies in the change of the acidic reagent composition in step 2): 5% hydrochloric acid and 3% hydrogen peroxide were mixed at a volume ratio of 5:1, resulting in a pH of 3.5. The mass concentration of ammonium persulfate in this acidic reagent was 0.5%. The activation treatment time was 10 seconds. The surface roughness Ra of the resulting substrate layer after activation treatment was 0.07 μm; the thickness of the surface oxide layer was 3 nm.

[0104] Example 4

[0105] Similar to the preparation method in Example 1, the main difference is that the activation treatment in step 2) is carried out by electrochemical anodic oxidation: using copper-nickel alloy foil as the anode and a lead plate as the cathode, in a 10% sulfuric acid solution, with a current density of 1 A / dm³. 2 The activation treatment time was 5 seconds. The surface roughness of the substrate layer after activation treatment was Ra=0.12μm; the thickness of the surface oxide layer was 5nm.

[0106] Example 5

[0107] Similar to the preparation method in Example 1, the main difference lies in the following: In step 2), the composition of the acidic reagent is changed: 2% (w / w) dilute sulfuric acid and 1% (w / w) hydrogen peroxide are mixed at a volume ratio of 10:1, with a pH of 3.8. The mass concentration of hydrogen peroxide in this acidic reagent is 0.3%. The activation treatment time is 15 seconds. The surface roughness Ra of the resulting substrate layer after activation treatment is 0.05 μm; the thickness of the surface oxide layer is 2 nm.

[0108] Example 6

[0109] Similar to the preparation method in Example 1, the main difference lies in the following: In step 2), the composition of the acidic reagent is changed: 20% (w / w) dilute sulfuric acid and 10 g / L ammonium persulfate are mixed at a volume ratio of 10:1, with a pH of 1. The mass concentration of ammonium persulfate in this acidic reagent is 0.9%. The activation treatment time is 15 s. The surface roughness Ra of the resulting substrate layer after activation treatment is 0.20 μm; the thickness of the surface oxide layer is 5 nm.

[0110] Comparative Example 1

[0111] Similar to the preparation method in Example 1, the main difference is that step 2 is omitted, so that no elemental gradient diffusion region can be formed at the interface between the substrate layer and the transition layer. At this time, the surface roughness of the substrate layer Ra=0.31μm; the thickness of the surface oxide layer is 20nm.

[0112] Comparative Example 2

[0113] Similar to the preparation method in Example 1, the main difference is that step 3 is omitted, so that the resulting composite current collector does not contain a transition layer.

[0114] Comparative Example 3

[0115] The preparation method is similar to that of Example 1, the main difference being that steps 2) to 4) are omitted.

[0116] Comparative Example 4

[0117] Similar to the preparation method in Example 1, the main difference is that in step 2), the activation treatment time is 3s, the surface roughness Ra of the substrate layer obtained after activation is 0.28μm, and the thickness of the surface oxide layer is 15nm.

[0118] Comparative Example 5

[0119] Similar to the preparation method in Example 1, the main difference is that in step 2), the activation treatment time is 25s, the surface roughness Ra of the substrate layer obtained after activation is 0.22μm, and the thickness of the surface oxide layer is 8nm.

[0120] The composite current collectors prepared in the above embodiments and comparative examples were subjected to relevant performance tests, and the test results are shown in Table 1 below. In Table 1, Ra and Rz refer to the surface roughness Ra and Rz of the substrate layer, respectively; the oxide layer thickness refers to the oxide layer thickness on the surface of the substrate layer; resistivity, tensile strength, and elongation all refer to the resistivity, tensile strength, and elongation of the composite current collector; " / " represents the absence of an elemental gradient diffusion region.

[0121] The test conditions or standards for each performance test item are as follows:

[0122] 1. Surface roughness Ra and Rz: Rz: Tested according to GB / T 10610-2009; Ra: Tested according to JIS B 0601.

[0123] 2. Oxide layer thickness: measured using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

[0124] 3. Tensile strength and elongation: Tensile elongation: Tested according to GB / T 228.1-2021.

[0125] 4. Interface adhesion: Tested in accordance with GB / T 4677.13-2007.

[0126] 5. Cross-cut test: The test shall be conducted in accordance with GB / T 9286-1998.

[0127] 6. Contact resistance change rate after 200 cycles: Tested according to EIA-364-23.

[0128] 7. Thermal cycling test (-40°C~80°C, 10 cycles): Refer to IPC-TM-650 2.6.7 for testing.

[0129] Table 1

[0130]

[0131] Table 2

[0132]

[0133] A comparison of Examples 1-6 with Comparative Example 1 shows that Comparative Example 1 does not perform surface activation treatment on the alloy substrate, resulting in a thicker oxide layer and higher surface roughness on the substrate surface. This makes it difficult to form an element gradient diffusion region, leading to weaker interfacial bonding and poorer cycle stability. In contrast, the element gradient diffusion region formed in Example 1 can be seen in [reference needed]. Figure 2 .

[0134] A comparison of Examples 1-6 with Comparative Examples 2-3 shows that Comparative Example 2 does not have a transition layer, resulting in poor cycle stability and contact resistance; Comparative Example 3 only contains a substrate layer, and its cycle stability and contact resistance are even worse than those of Comparative Example 2.

[0135] A comparison of Examples 1-6 with Comparative Examples 4-5 shows that when the activation treatment time in Comparative Examples 4-5 exceeds the range defined in this application, the surface roughness of the substrate layer is larger and the oxide layer thickness is thicker. Compared with Examples 1-6, it is difficult to form an element gradient diffusion zone, resulting in poor interfacial bonding and poor cycle stability.

[0136] 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.

[0137] 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 composite current collector, characterized in that, Includes: a substrate layer, a transition layer disposed on at least one side of the substrate layer, and a conductive layer disposed on the transition layer; The material of the base layer includes one or more of copper-nickel alloy, copper-tin alloy and iron-nickel alloy, and the elements contained in the transition layer are not exactly the same as those contained in the base layer; At the interface where the matrix layer and the transition layer are in contact, there is an element gradient diffusion region. Within the element gradient diffusion region, the elements contained in the matrix layer and the elements contained in the transition layer diffuse into each other and their concentrations are distributed in a gradient along the thickness direction.

2. The composite current collector according to claim 1, characterized in that, One or more of the following conditions must be met: (1) The gradient distribution satisfies the following: along the thickness direction, the element gradient diffusion region moves from the side relatively close to the matrix layer to the side relatively close to the transition layer, the atomic percentage concentration of the elements contained in the matrix layer gradually decreases, and the atomic percentage concentration of the elements contained in the transition layer gradually increases; (2) The thickness of the element gradient diffusion region is 10nm~50nm, and can be selected as 30nm~50nm.

3. The composite current collector according to claim 1 or 2, characterized in that, One or more of the following conditions must be met: (1) The surface roughness Ra of the substrate layer is 0.05μm~0.20μm, and Rz is 0.23μm~1.15μm; (2) The thickness of the oxide layer on the surface of the substrate layer is ≤5nm; (3) The material of the transition layer includes one or more of nickel, copper, cobalt and cobalt alloys; (4) The thickness of the transition layer is 0.1μm~0.5μm.

4. The composite current collector according to claim 1 or 2, characterized in that, One or more of the following conditions must be met: (1) The thickness of the substrate layer is 5μm~20μm; (2) The thickness of the substrate layer is 70% to 95% of the total thickness of the composite current collector; (3) The material of the conductive layer includes one or more of copper, silver, gold and zinc, and the types of elements contained in the conductive layer are different from those contained in the transition layer; (4) The thickness of the conductive layer is 0.1μm~2μm.

5. The composite current collector according to claim 1 or 2, characterized in that, One or more of the following conditions must be met: (1) The tensile strength of the composite current collector is ≥1000MPa; (2) The volume resistivity of the composite current collector is ≤3.5 μΩ·cm.

6. A method for preparing a composite current collector, characterized in that, include: The surface of the alloy substrate is activated by an acidic reagent containing an oxidant, or by an electrochemical anodic oxidation method, to obtain a substrate layer. The material of the substrate layer includes one or more of copper-nickel alloy, copper-tin alloy, and iron-nickel alloy. The activation treatment time is 5s to 20s. A transition layer with a different element type than that contained in the substrate layer is electrodeposited on at least one side of the substrate layer, so that an element gradient diffusion region is formed at the interface where the substrate layer and the transition layer are in contact. Within the element gradient diffusion region, the elements contained in the substrate layer and the elements contained in the transition layer diffuse into each other and the concentration is distributed in a gradient along the thickness direction. A conductive layer is prepared on the transition layer to prepare a composite current collector.

7. The preparation method according to claim 6, characterized in that, One or more of the following conditions must be met: (1) The pH value of the acidic reagent is 1~4.5, and can be selected as 2.5~4.5; (2) The oxidizing agent includes hydrogen peroxide and / or ammonium persulfate; (3) The mass concentration of the oxidant in the acidic reagent is 0.3% to 5%.

8. The preparation method according to claim 6 or 7, characterized in that, One or more of the following conditions must be met: (1) The surface roughness Ra of the substrate layer is 0.05μm~0.20μm, and Rz is 0.23μm~1.15μm; (2) The thickness of the oxide layer on the surface of the substrate layer is ≤5nm.

9. A negative electrode sheet, characterized in that, The composite current collector includes the composite current collector described in any one of claims 1 to 5 or the composite current collector prepared by the preparation method described in any one of claims 6 to 8.

10. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 9.

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