Current collector, method for manufacturing the same, secondary battery, and electric device

Abstract

The application provides a current collector and a preparation method thereof, a secondary battery and an electric device. The current collector comprises a nickel-containing alloy layer and a metal layer arranged on at least one side of the nickel-containing alloy layer, the nickel-containing alloy layer comprises a nickel element and a first metal element other than the nickel element, the first metal element comprises one or more of Fe, Zn, Ti, V, Cr, Mn or Co, the metal layer comprises one or more of Cu, Ni, Zn or Cr, and a thickness variance of the metal layer is less than or equal to 0.5 μm 2 .

Description

[0001] Related applications

[0002] This application claims priority to Chinese Patent Application No. 2025101735554, filed on February 17, 2025, entitled "Battery cell, battery device, power supply device and current collector", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to current collectors and their preparation methods, secondary batteries and electrical devices. Background Technology

[0004] In recent years, the application range of secondary batteries, such as lithium-ion batteries, has become increasingly wide. They are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. While secondary batteries have achieved significant development, the problem of heat generation remains quite serious. This heat generation issue can easily lead to the risk of thermal runaway, making it difficult to balance good cycle performance with a low risk of thermal runaway. Summary of the Invention

[0005] In view of the above problems, this application provides a current collector and its preparation method, a secondary battery and an electrical device, which aim to improve the heat generation problem of the battery while taking into account good cycle performance.

[0006] A first aspect of this application provides a current collector comprising a nickel-containing alloy layer and a metal layer disposed on at least one side of the nickel-containing alloy layer. The nickel-containing alloy layer comprises nickel and a first metal element other than nickel, wherein the first metal element comprises one or more of Fe, Zn, Ti, V, Cr, Mn, or Co. The metal layer comprises one or more of Cu, Ni, Zn, and Cr, and the thickness variance of the metal layer is less than or equal to 0.5 μm. 2 .

[0007] The aforementioned current collector, with its nickel alloy layer (e.g., nickel-iron alloy layer), possesses high tensile strength and can effectively resist the expansion of the electrode. For example, when used as a negative electrode current collector, it can resist the expansion of high-energy-density negative electrode active materials such as silicon-based materials, reducing electrode cracking due to expansion and improving battery cycle performance. Introducing a metal layer containing the aforementioned specific elements into the nickel alloy layer can improve the conductivity of the current collector, while the thickness variance of the metal layer is less than or equal to 0.5 μm. 2 It has good thickness uniformity, so when this current collector is used in batteries, the sheet resistance of the current collector is reduced and the DC internal resistance (DCR) of the battery is improved, so that the battery can achieve both good cycle performance and low risk of thermal runaway.

[0008] In some embodiments, the thickness variance of the metal layer is 0.02 μm. 2 ~0.2μm 2 .

[0009] By controlling the thickness variance within this range, the current collector can achieve both low sheet resistance and high tensile strength. Specifically, the thickness variance of the metal layer is controlled at 0.2 μm. 2 The following are beneficial for reducing the sheet resistance of the current collector, with the thickness variance of the metal layer controlled within 0.02 μm. 2 The above results in a moderate degree of non-uniformity in the metal layer. The "atypical" advantage of this non-uniform coating is that the metal layer is thinner in these areas, and may even expose the nickel-iron substrate in some places. These areas are the "strong points" of the tensile strength of the material in the current collector. An overly uniform coating eliminates these "strong points" and instead reduces the tensile strength of the current collector.

[0010] In some embodiments, the thickness of the metal layer is 0.5 μm to 2 μm, and optionally 0.5 μm to 1 μm.

[0011] In some embodiments, the total thickness of the metal layer accounts for 10% to 40% based on the total thickness of the current collector.

[0012] Having the thickness or thickness percentage of the metal layer within the above range is beneficial for balancing the tensile strength and elongation at break of the current collector, reducing the risk of current collector breakage during long cycles and causing battery failure, and improving battery cycle life.

[0013] In some embodiments, the thickness of the nickel alloy layer is 3μm to 8μm, and optionally 4μm to 6μm.

[0014] In some embodiments, the thickness of the nickel alloy layer accounts for 60% to 90% based on the total thickness of the current collector.

[0015] If the thickness or thickness ratio of the nickel alloy layer is within the above range, the bending resistance of the current collector can be further improved through the coordinated effect of different structures or components in different foil layers, reducing the probability of the current collector breaking in the inner ring of the wound cell with high bending degree, thus causing battery failure.

[0016] In some embodiments, the sheet resistance of the current collector is less than or equal to 15 mΩ / □, and can be selected as 2 mΩ / □ to 15 mΩ / □.

[0017] This current collector has a low sheet resistance, which helps to reduce the battery DCR and improve the battery heat generation problem.

[0018] In some embodiments, the nickel content in the nickel alloy layer is 40% to 90% by mass, and optionally 70% to 80%.

[0019] In some implementations, one or more of the following characteristics are satisfied:

[0020] (1) The mass content of the first metallic element in the nickel-containing alloy layer is 10% to 60%, and can be selected as 15% to 35%;

[0021] (2) The mass content of the nickel element and the first metal element in the nickel-containing alloy layer is ≥95%.

[0022] In some embodiments, the tensile strength of the current collector is ≥1700MPa, and can be selected as 1710MPa~2000MPa.

[0023] The aforementioned current collector has high tensile strength, which increases the cumulative strain that the battery cell can withstand along its length, thus improving the cell's resistance to expansion, reducing the risk of electrode breakage, and improving the cycle life of the battery cell.

[0024] In some embodiments, the elongation at break of the current collector is ≥3%, optionally 3%~8%;

[0025] By controlling the fracture elongation δ of the current collector within the above range, the possibility of stress concentration causing the current collector to fracture in the length direction is reduced, thereby reducing the fracture risk of the current collector and the electrode with the current collector, improving the overall tolerable cumulative strain of the battery cell, and improving the cycle life of the battery cell.

[0026] In some embodiments, the metal layer comprises a crystalline structure; optionally, the average grain size of the metal layer is 90 nm to 400 nm, and optionally 100 nm to 300 nm.

[0027] Large grain size metal layers have good plastic deformation ability, which is beneficial to improve the plasticity of the current collector and reduce the risk of battery failure caused by current collector fracture.

[0028] In some embodiments, the nickel-containing alloy layer comprises a crystalline structure; optionally, the average grain size of the nickel-containing alloy layer is 10 nm to 80 nm, and optionally 20 nm to 60 nm.

[0029] Controlling the average grain size of the nickel alloy layer within the aforementioned small range is beneficial because smaller grains are easier to orient, specifically, the strongest peak of the grain corresponds to the orientation of the crystal plane, resulting in higher lateral tensile strength and lateral elongation at break of the current collector. Furthermore, it also ensures the good bending resistance of the nickel alloy layer, thus giving the current collector good bending resistance as well. Compared to stacked electrode assemblies, wound electrode assemblies experience greater stress on the electrodes. This stress gradually accumulates, especially on the outer electrodes along the winding direction, accelerating fracture and significantly worsening the cycle life at the end of the wound cell cycle. Therefore, using the aforementioned current collector for the negative electrode of the wound electrode assembly further increases the cumulative strain that the battery cell can withstand along the winding direction, reducing the risk of electrode fracture and improving the cycle life of the battery cell.

[0030] A second aspect of this application provides a method for preparing a current collector, comprising the following steps:

[0031] An anode, a first electroplating solution, and a cathode are provided for a first electroplating process to form a nickel-containing alloy layer on the surface of the cathode; after the electroplating process, the nickel-containing alloy layer is separated from the surface of the cathode.

[0032] A second electroplating treatment is performed on the nickel alloy layer using a second electroplating solution to form a metal layer on at least one side of the nickel alloy layer.

[0033] The first electroplating solution includes a nickel source and a first metal source. The first metal element in the first metal source includes one or more of Fe, Zn, Ti, V, Cr, Mn, or Co. The second electroplating solution includes a metal source and additives. In the electroplating process for forming the metal layer, the conveyor speed of the nickel alloy layer is less than or equal to 3 m / min. The metal element in the metal source of the second electroplating solution includes one or more of Cu, Ni, Zn, and Cr. The additives include one or more of sodium polydithiopropane sulfonate, sodium 3-mercapto-1-propane sulfonate, sodium thiazolinyl dithiopropane sulfonate, or dithiopropane sulfonic acid.

[0034] The above-mentioned method for preparing the current collector involves first electroplating to form a nickel-containing alloy layer, and then forming a metal layer on at least one side of the nickel-containing alloy layer. The additive contains both sulfonic acid groups and thio groups or mercapto groups. The sulfonic acid groups significantly reduce the surface tension of the plating solution, while the thio groups or mercapto groups can form complexes with metal ions, reducing the probability of disordered deposition. Furthermore, the additive does not contain long carbon chain groups, making it less prone to agglomeration in high-temperature plating solutions and exhibiting good stability. This promotes uniform distribution of metal ions and reduces the problem of uneven coating thickness caused by tip effects. Simultaneously, the second current collector is controlled... During the plating process, keeping the conveyor belt speed of the nickel alloy layer within the aforementioned smaller range reduces the splashing of the plating solution, preventing it from depositing on the conductive roller and forming a copper plating layer. This also lowers the risk of uneven deposition in different areas of the metal layer, resulting in better consistency in the amount of conductive metal material deposited on the nickel alloy layer. Furthermore, a slower conveyor belt speed means longer contact time between the deposition area and the plating solution, leading to more thorough deposition. This improves the uniformity of the metal layer thickness, resulting in a thickness variance of less than or equal to 0.5 μm. 2 The current collector prepared by this method is used in batteries. Thanks to the reduced sheet resistance of the current collector, the DC internal resistance (DCR) of the battery is significantly improved, thus enabling the battery to achieve both good cycle performance and a lower risk of thermal runaway.

[0035] In some embodiments, the concentration of the metal source in the second electroplating solution is 80 g / L to 160 g / L, and optionally 120 g / L to 140 g / L.

[0036] In some embodiments, the concentration of the additive in the second electroplating solution is 1 g / L to 5 g / L.

[0037] In some embodiments, the second electroplating solution further includes a conductive agent, which includes a chloride. Optionally, the chloride includes one or more of copper chloride or sodium chloride. Optionally, the concentration of the conductive agent in the second electroplating solution is 5 g / L to 25 g / L. The conductive agent can enhance ion transport capability and improve deposition efficiency.

[0038] In some embodiments, the current density in the second electroplating process is 2 A / dm². 2 ~8A / dm 2 ;

[0039] By controlling the conveyor speed of the nickel alloy layer in the second electroplating process within the aforementioned small range, and further controlling the current density in the second electroplating process within the aforementioned small range, the deposition rate of the metal layer is controlled to be slower, which is beneficial to improve the density of the grain arrangement and thus improve the thickness uniformity of the metal layer.

[0040] In some embodiments, during the second electroplating process, the conveyor speed of the nickel alloy layer is 1 m / min to 3 m / min.

[0041] By controlling the conveyor belt speed within this range, the uniformity of the metal layer thickness can be improved while maintaining high production efficiency.

[0042] In some embodiments, during the first electroplating process, the surface roughness Ra of the cathode is 0.1 μm to 0.3 μm.

[0043] Adjusting the surface roughness Ra of the cathode to 0.1μm~0.3μm, that is, adjusting the surface uniformity of the substrate for forming the nickel alloy layer, is beneficial to improving the thickness uniformity of the nickel alloy layer; the thickness uniformity of the nickel alloy layer will also affect the thickness uniformity of the metal layer, which in turn is beneficial to improving the thickness uniformity of the metal layer.

[0044] In some embodiments, the current density in the first electroplating process is 5 A / dm². 2 ~15A / dm 2 Adjusting the current density within this range is beneficial for improving deposition efficiency.

[0045] In some embodiments, during the first electroplating process, the difference between the maximum and minimum distance between the roller surface of the anode and the roller surface of the cathode is 0 to 1 cm.

[0046] The smaller the difference between the maximum and minimum distances between the anode and cathode roller surfaces, the more parallel the positions of the anode and cathode rollers are, and the more even the distances between them are. This improves the uniformity of the nickel-containing alloy layer along the length of the cathode roller.

[0047] In some embodiments, the concentration of the nickel source in the first electroplating solution is 200 g / L to 250 g / L.

[0048] In some embodiments, the nickel source includes one or more of nickel sulfate, nickel chloride, or nickel carbonate.

[0049] In some embodiments, the first metal source includes an Fe source, and the concentration of the Fe source in the first electroplating solution is 30 g / L to 80 g / L.

[0050] In some embodiments, the first electroplating solution further includes a complexing agent, which includes one or more of sodium citrate, sodium gluconate, tartaric acid, or lactic acid; optionally, the concentration of the complexing agent in the first electroplating solution is 20 g / L to 40 g / L.

[0051] In some embodiments, the first electroplating solution further includes a brightener, which includes one or more of sodium saccharin, saccharin, 1,4-butynediol, butynediol diethoxy ether, polyethylene glycol, coumarin, formaldehyde, and pyridine derivatives. Optionally, the concentration of the brightener in the first electroplating solution is 1 g / L to 10 g / L.

[0052] In some embodiments, the first electroplating solution further includes a conductive agent, which includes one or more of sodium chloride, hydrochloric acid, or ammonium chloride; optionally, the concentration of the conductive agent in the first electroplating solution is 10 g / L to 50 g / L.

[0053] In some embodiments, the first electroplating solution further includes a stabilizer, which includes one or more of boric acid, citric acid, or fluoroborate; optionally, the concentration of the stabilizer in the electroplating solution is 20 g / L to 80 g / L.

[0054] In a third aspect, this application provides a secondary battery, including a current collector prepared by the method for preparing the current collector provided in the first aspect of this application or the current collector provided in the second aspect of this application.

[0055] In some embodiments, an electrode assembly is included, the electrode assembly including a positive electrode and a negative electrode, the negative electrode including a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer including a negative active material, and the negative current collector including a current collector provided by the first aspect of this application or a current collector prepared by the preparation method of the current collector provided by the second aspect of this application.

[0056] In some embodiments, the electrode assembly is a wound structure, and the length direction of the current collector is the same as the winding direction of the electrode assembly;

[0057] Optionally, the thickness of the electrode assembly is 10mm to 50mm;

[0058] Optionally, the electrode assembly includes a corner region and a straight region, wherein the ratio of the length of the straight region to the length of the corner region of the electrode assembly is 1 to 10.

[0059] In some embodiments, the negative electrode active material comprises a silicon-based material; optionally, the silicon-based material has a mass content of ≥20% in the negative electrode active layer, and is optionally 20%~60%.

[0060] In a fourth aspect, this application provides an electrical device, including a current collector provided in the first aspect of this application, a current collector prepared by the method for preparing the current collector provided in the second aspect of this application, or a secondary battery provided in the third aspect of this application.

[0061] The electrical device of this application includes the secondary battery provided in this application, and therefore has at least the same advantages as the secondary battery.

[0062] Details of one or more embodiments of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0063] To better describe and illustrate the embodiments or examples provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments or examples, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0064] Figure 1 This is a schematic diagram of a single cell of a secondary battery according to one embodiment of this application.

[0065] Figure 2 yes Figure 1 An exploded view of a battery cell according to one embodiment of this application is shown.

[0066] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0067] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0068] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0069] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0070] Figure 7 This is an elemental distribution diagram of the current collector prepared in Example 3 of this application.

[0071] Explanation of reference numerals in the attached figures:

[0072] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Battery module; 5. Battery cell; 51. Housing; 52. Electrode assembly; 53. Cover plate; 6. Electrical device. Detailed Implementation

[0073] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0074] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be independently included or excluded, and they can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this document; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, stating that a parameter is an integer ≥2 is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, stating that a parameter is an integer selected from "2~10" is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0075] In this application, the terms "multiple" or "various" are used unless otherwise specified, referring to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0076] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0077] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0078] Those skilled in the art will understand that the order in which the steps are written in the methods of various embodiments or examples does not imply a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0079] In this application, unless otherwise specified, A (e.g., B) means that B is a non-limiting example of A, and it is understood that A is not limited to B.

[0080] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it means that it is selected from either "with" or "without." If there are multiple "optional" entries in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" entry shall be independent.

[0081] During multiple charge-discharge cycles, the electrochemical reactions, structural changes, and side reactions of the electrode materials collectively lead to a gradual increase in electrode thickness, causing the electrodes to crack due to expansion. This phenomenon is more pronounced in batteries containing silicon-based materials (especially high-silicon systems) and wound batteries. During battery cycling, the expansion of silicon-based materials causes stress to accumulate, leading to electrode cracking. The outer ring of wound cells experiences the greatest stress, making it prone to electrode breakage. Nickel alloy layers (such as nickel-iron alloy foil) have high tensile strength and can effectively resist electrode expansion when used as current collectors. For example, when used as negative electrode current collectors, they can resist the expansion of high-energy-density negative electrode active materials such as silicon-based materials, reducing electrode cracking and improving battery cycle performance. However, nickel alloy layers are limited by their material composition; they have low conductivity and high sheet resistance, resulting in poor overcurrent capacity. This deteriorates the battery's DC internal resistance (DCR), leading to severe heat generation and the risk of thermal runaway, further worsening battery cycle performance. Therefore, it is difficult to achieve both good cycling performance and a low risk of thermal runaway.

[0082] Based on the aforementioned technical problems, this application introduces a metal layer containing the specific elements mentioned above into the nickel alloy layer, which can improve the conductivity of the current collector. However, when the nickel alloy layer is introduced into the electroplating solution through the cathode roller to form the metal layer, some of the electroplating solution is prone to splashing out, causing losses. For example, some of the splashed solution is deposited on the cathode roller, resulting in a thinner metal layer deposited on the nickel alloy layer. Consequently, it is difficult to ensure the uniformity of the metal layer thickness. When used in batteries, it was found that the sheet resistance of the current collector is still relatively large, and the DC internal resistance (DCR) of the battery cannot be improved. Therefore, the problem of not being able to simultaneously achieve good cycle performance and low thermal runaway risk remains unsolved.

[0083] Therefore, this application provides an improved current collector and its preparation method, which can produce a current collector with better thickness uniformity.

[0084] One embodiment of this application provides a current collector, comprising a nickel-containing alloy layer and a metal layer disposed on at least one side of the nickel-containing alloy layer. The nickel-containing alloy layer comprises nickel and a first metal element other than nickel. The first metal element includes one or more of Fe, Zn, Ti, V, Cr, Mn, or Co. The metal layer includes one or more of Cu, Ni, Zn, and Cr. The thickness variance of the metal layer is less than or equal to 0.5 μm. 2 .

[0085] The current collector described in this application, including nickel-iron alloy foil and other nickel-containing alloy layers, possesses high tensile strength. As a current collector, it can effectively resist the expansion of the electrode. For example, when used as a negative electrode current collector, it can resist the expansion of high-energy-density negative electrode active materials such as silicon-based materials, reducing the possibility of electrode cracking due to expansion and improving the cycle performance of the battery. Introducing a metal layer containing the aforementioned specific elements into the nickel-containing alloy layer can improve the conductivity of the current collector, while the thickness variance of the metal layer is less than or equal to 0.5 μm. 2 It has good thickness uniformity, so when this current collector is used in batteries, the sheet resistance of the current collector is reduced and the DC internal resistance (DCR) of the battery is improved, so that the battery can achieve both good cycle performance and low risk of thermal runaway.

[0086] In addition, the Cu, Ni, Zn or Cr elements in the metal layer are highly ductile metal elements, which can effectively improve the bending resistance of the current collector and improve the cycle life of the battery cell without significantly sacrificing the strength of the current collector.

[0087] The aforementioned first metallic element possesses both high strength and ductility. The nickel-containing alloy layer improves the fracture elongation and bendability of the current collector by alloying nickel with the first metallic element. This allows the current collector to expand and contract during cycling, thereby reducing the risk of electrode breakage. It also helps improve the current collector's resistance to expansion during long cycles and increases the cycle life of the battery cell.

[0088] The elemental composition of the nickel-containing alloy layer can be obtained by energy dispersive spectroscopy (EDS) or plasma atomic emission spectrometry (PISA). The mass content of the first element in the nickel-containing alloy layer can be obtained by separating the nickel-containing alloy layer from the current collector and then analyzing the nickel-containing alloy layer by PISA.

[0089] Method for testing the thickness of each layer of the current collector: Randomly select several (e.g., 10) 1cm×1cm square samples from the current collector. Place the samples on the test stage and bombard the sample surface with an argon ion beam to obtain a cross-sectional photograph of the current collector. Then, obtain the cross-sectional photograph and scale bar using a Zeiss scanning electron microscope. By comparing with the scale bar, randomly test several (e.g., 10) locations on each sample to obtain the thickness of the nickel alloy layer and the metal layer at each location. In this way, obtain the thickness values ​​of the nickel alloy layer and the metal layer at each location in each sample (e.g., 100 locations). Take the arithmetic mean of the thickness values ​​of the nickel alloy layer at each location (e.g., 100 locations) as the thickness of the nickel alloy layer in the negative electrode current collector. Take the arithmetic mean of the thickness values ​​of the metal layer at each location (e.g., 100 locations) as the thickness of the metal layer in the negative electrode current collector.

[0090] Calculation of the thickness variance of the metal layer: The thickness test values ​​of the nickel alloy layer at each of the above locations (e.g., 100 locations) are used to calculate the thickness variance of the nickel alloy layer.

[0091] The formula for calculating the variance of the above-mentioned metal layer thickness is as follows:

[0092] ;

[0093] in Xi is the arithmetic mean of the metal layer thickness test values, where Xi is the metal layer thickness test value at each location (e.g., 100 locations), Σ represents summation, and n is the number of test locations (e.g., 100 locations).

[0094] In some embodiments, the thickness variance of the metal layer may be 0.001 μm. 2 0.005μm 2 0.01μm 2 0.02μm 2 0.03μm 2 0.05μm 2 0.1μm 2 0.2μm 2 0.25μm 2 0.3μm 2 0.4μm 2 0.5μm 2 Or any value between the two, for example, 0.001 μm2 ~0.5μm 2 Optional, less than or equal to 0.4μm 2 In one example, the thickness variance of the metal layer is 0.02 μm. 2 ~0.2μm 2 By controlling the thickness variance within this range, the current collector can achieve both low sheet resistance and high tensile strength. Specifically, the thickness variance of the metal layer is controlled at 0.2 μm. 2 The following are beneficial for reducing the sheet resistance of the current collector, with the thickness variance of the metal layer controlled within 0.02 μm. 2 The above results in a moderate degree of non-uniformity in the metal layer. The "atypical" advantage of this non-uniform coating is that the metal layer is thinner in these areas, and may even expose the nickel-iron substrate in some places. These areas are the "strong points" of the tensile strength of the material in the current collector. An overly uniform coating eliminates these "strong points" and instead reduces the tensile strength of the current collector.

[0095] Furthermore, the metal layer comprises a metal of one of Cu, Ni, Zn or Cr, or an alloy comprising one or more of Cu, Ni, Zn or Cr, wherein the alloy comprises an alloy formed of at least two elements of Cu, Ni, Zn or Cr, or an alloy formed of one of the aforementioned elements of Cu, Ni, Zn or Cr with other elements.

[0096] In some embodiments, the metal layer includes Cu, with a Cu content of ≥99% by mass. The metal layer utilizes copper foil, which has high conductivity and low cost, thus improving the overall conductivity of the current collector, thereby increasing the conductivity of the electrode, reducing the battery's DCR internal resistance, and ultimately improving the battery's power performance. Furthermore, including Cu or using pure copper in the metal layer further improves the ductility of the second metal foil layer and enhances the current collector's bending resistance.

[0097] In some embodiments, the thickness of the metal layer is 0.5 μm to 2 μm, optionally 0.5 μm to 1 μm. As an example, the thickness of the metal layer can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, or any value between two of these. Understandably, the thickness of the metal layer here refers to the thickness of one side of the metal layer.

[0098] In some embodiments, the total thickness of the metal layer accounts for 10% to 70% of the total thickness of the current collector, and can be selected as 10% to 40%. As an example, the total thickness percentage of the metal layer, based on the total thickness of the current collector, can be selected as 10%, 15%, 20%, 25%, 30%, 1 / 3, 35%, 40%, 50%, 60%, 70%, or any value range between two of these. Understandably, when both surfaces of the nickel alloy layer are provided with metal layers, the total thickness percentage of the metal layer refers to the sum of the thicknesses of the metal layers on both sides.

[0099] Having the thickness or thickness percentage of the metal layer within the above range is beneficial for balancing the tensile strength and elongation at break of the current collector, reducing the risk of current collector breakage during long cycles and causing battery failure, and improving battery cycle life.

[0100] In some embodiments, the thickness of the nickel alloy layer is 3 μm to 8 μm, optionally 4 μm to 6 μm. As an example, the thickness of the nickel alloy layer can be 3 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, or any value range between the two.

[0101] A nickel alloy layer thickness of 3 μm or more helps maintain good structural stability of the negative electrode current collector, further improving the battery's cycle performance. A negative electrode current collector thickness of less than 8 μm allows for a smaller current collector thickness, reducing its weight and thus contributing to increased battery energy density.

[0102] In some embodiments, the thickness of the nickel alloy layer is 30% to 90% based on the total thickness of the current collector, and can be selected as 60% to 90% or 30% to 85%. Based on the total thickness of the current collector, the thickness of the nickel alloy layer can be selected as 30%, 40%, 50%, 60%, 65%, 2 / 3, 70%, 75%, 80%, 85%, 90%, or any value range between the two.

[0103] If the thickness or thickness ratio of the nickel alloy layer is within the above range, the bending resistance of the current collector can be further improved through the coordinated effect of different structures or components in different foil layers, reducing the probability of the current collector breaking in the inner ring of the wound cell with high bending degree, thus causing battery failure.

[0104] In some embodiments, the total thickness of the current collector is 2 μm to 15 μm, optionally 4 μm to 12 μm, or optionally 4 μm to 10 μm. As an example, the thickness of the current collector can be selected from 2 μm, 3 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 14 μm, 15 μm, or any value range between the two. For example, the total thickness of the current collector can be 3 μm to 12 μm, 3 μm to 10 μm, 3 μm to 9 μm, 3 μm to 8 μm, 4 μm to 12 μm, 4 μm to 10 μm, 4 μm to 9 μm, 4 μm to 8 μm, etc.

[0105] The current collector has a low thickness, which can increase the loading of active materials, thus improving battery mass energy density and / or volumetric energy density while increasing battery cycle life.

[0106] In some implementations, the thickness range of the current collector is less than or equal to 0.5 μm.

[0107] In some implementations, the thickness range of the current collector can be selected as 0, 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, or any value range between the two.

[0108] The range of current collector thickness can be tested using methods known in the art. As an example, the current collector cross-section is collected at different sites using argon ion polishing technology. For wound cells, the minimum distance between different sites is 1m. The thickness of the current collector cross-section at different sites is measured under an electron microscope, obtaining no less than 10 data points. The maximum thickness of the current collector minus the minimum thickness of the current collector in the collected data is taken as the range of current collector thickness.

[0109] The fact that the thickness variation of the current collector is within the above range indicates that the current collector has good thickness consistency, which can reduce the probability of stress concentration in local areas, reduce the risk of premature current collector failure, and improve the cycle life of the battery.

[0110] In some implementations, the coefficient of variation of the current collector thickness is less than or equal to 0.5%; and / or the coefficient of variation of the current collector surface density is less than or equal to 0.5%.

[0111] In some implementations, the coefficient of variation of the current collector thickness can be selected as 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value range between the two.

[0112] The coefficient of variation of the current collector thickness can be tested using methods known in the art. As an example, cross-sections of the current collector are collected in different regions using argon ion polishing technology. For wound cells, the minimum distance between different regions on the unfolded current collector is 1 m. The thickness of the current collector cross-section at different regions is measured under an electron microscope, obtaining no fewer than 10 data points. The coefficient of variation of the current collector thickness is calculated using the following formula, where φ represents the current collector thickness, and n represents the number of samples. This represents the average thickness of the current collector. The formula is shown below:

[0113] .

[0114] In some implementations, the coefficient of variation of the current collector surface density can be selected as 0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, or any value range between the two.

[0115] Sampling and calculation were performed using the same method as described above for the coefficient of variation of thickness. The specific method for measuring the areal density of each sample is as follows: For example, the battery was placed in a 25°C oven and left to stand for 2 hours. Once the battery temperature was maintained at 25°C, the battery was discharged at a constant current of 1 / 3C to 2.0V. The battery was then disassembled to obtain the electrode, the film layer on it was wiped off, and it was cut into small circular pieces with an area of ​​S0. The mass of these pieces was weighed and recorded as M0. The areal density of the current collector was M0 / S0.

[0116] When the coefficient of variation of the current collector thickness or areal density is within the above range, the non-uniformity of the current collector thickness or areal density can be reduced, the possibility of current collector fracture caused by stress concentration can be reduced, the fracture elongation of the current collector can be improved, thereby increasing the fracture elongation of the electrode, increasing the cumulative strain that the battery can withstand, and improving the cycle life of the battery.

[0117] In some embodiments, the current collector includes a nickel-containing alloy layer and metal layers disposed on both sides of the nickel-containing alloy layer. Further, the current collector includes a nickel-containing alloy layer and copper layers disposed on both sides of the nickel-containing alloy layer. Further, the copper layers are electroplated copper layers.

[0118] In some embodiments, the metal layer comprises a crystalline structure. In other words, the metal particles or alloy particles in the metal layer have a crystalline structure.

[0119] Optionally, the average grain size of the metal layer is 90 nm to 400 nm, and optionally 100 nm to 300 nm. As an example, the average grain size of the metal layer can be 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 200 nm, 220 nm, 250 nm, 260 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, or any value range between the two. For example, the average grain size of the metal layer can be 90nm~380nm, 90nm~350nm, 90nm~320nm, 90nm~300nm, 90nm~260nm, 90nm~220nm, 90nm~200nm, 90nm~150nm, 100nm~400nm, 100nm~400nm, 100nm~380nm, 100nm~350nm, 100nm~320nm, 100nm~300nm, etc. The range of nanometer sizes includes 0nm, 100nm~260nm, 100nm~220nm, 100nm~200nm, 100nm~150nm, 110nm~400nm, 110nm~400nm, 110nm~380nm, 110nm~350nm, 110nm~320nm, 110nm~300nm, 110nm~260nm, 110nm~220nm, 110nm~200nm, and 110nm~150nm. Large-grain-size metal layers possess excellent plastic deformation capabilities, which helps improve the plasticity of the current collector and further reduces the risk of battery failure due to current collector fracture.

[0120] In this application, the average grain size of the metal layer can be tested using any method known in the art. For example, X-ray diffraction (XRD) can be performed on the metal layer in the current collector to analyze the average grain size of the nickel alloy layer. As an example, at 25°C, using CuKα rays as the X-ray source, a scanning speed of 2° / min and a scanning range of 10°~100° is used; an X-ray diffraction pattern is tested using an X-ray diffractometer, and the peak with the highest diffraction intensity in the X-ray diffraction pattern is used as a reference. The average grain size is calculated using the Scherrer formula D=Kλ / (βcosθ), where D is the average grain size, K is the Scherrer constant (0.89), λ is the X-ray wavelength (selectable wavelength in the test is 0.154nm), β is the full width at half maximum (FWHM) of the diffraction peak, and θ is the diffraction angle.

[0121] In some embodiments, the nickel-containing alloy layer comprises a crystalline structure. In other words, the alloy particles in the nickel-containing alloy layer have a crystalline structure.

[0122] Optionally, the average grain size of the nickel-containing alloy layer is 10 nm to 80 nm. As an example, the average grain size of the nickel-containing alloy layer can be 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 60 nm, 70 nm, 80 nm, or any value range between the two. For example, the average grain size of the nickel-containing alloy layer can be 10 nm to 60 nm, 10 nm to 50 nm, 10 nm to 40 nm, 15 nm to 60 nm, 15 nm to 50 nm, 15 nm to 40 nm, 20 nm to 60 nm, 20 nm to 50 nm, 20 nm to 40 nm, etc.

[0123] The average grain size of the nickel alloy layer can be adjusted by regulating the electroplating process, such as the nickel content. Controlling the average grain size within this smaller range is beneficial because smaller grains are more easily oriented, specifically, the strongest peak of the grain corresponds to the orientation of the crystal plane, resulting in higher tensile strength and elongation at break of the current collector. Furthermore, it also ensures good bending resistance of the nickel alloy layer, thus providing the current collector with good bending resistance as well. Compared to stacked electrode assemblies, wound electrode assemblies experience greater stress on the electrodes. This stress gradually accumulates, especially on the outer electrodes along the winding direction, accelerating fracture and significantly worsening the cycle life at the end of the wound cell cycle. Therefore, using the aforementioned current collector for the negative electrode of the wound electrode assembly can further increase the cumulative strain that the battery cell can withstand along the winding direction, reducing the risk of electrode fracture and improving the cycle life of the battery cell. Specifically, when the nickel alloy layer is a nickel-iron alloy foil, the strongest peak of the grain corresponds to the (111) crystal plane.

[0124] In this application, the average grain size of the nickel alloy layer can be tested using any method known in the art. For example, X-ray diffraction (XRD) can be performed on the nickel alloy layer in the current collector to analyze the average grain size. As an example, at 25°C, using CuKα rays as the X-ray source, a scanning speed of 2° / min and a scanning range of 10°~100° is used; an X-ray diffraction pattern is tested using an X-ray diffractometer, and the peak with the highest diffraction intensity in the X-ray diffraction pattern is used as a reference. The average grain size is calculated using the Scherrer formula D=Kλ / (βcosθ), where D is the average grain size, K is the Scherrer constant (0.89), λ is the X-ray wavelength (selectable wavelength in the test is 0.154nm), β is the full width at half maximum (FWHM) of the diffraction peak, and θ is the diffraction angle.

[0125] The nickel alloy layer improves the tensile strength and elongation at break of the current collector through grain refinement; the large grain size of the metal layer has good plastic deformation ability, which is beneficial to improving the plasticity of the current collector; under the synergistic effect of the multi-layer structure of the current collector, the risk of battery failure caused by current collector fracture is reduced.

[0126] It is understandable that X-ray diffraction (XRD) tests on different metal foil layers in the current collector can be achieved by selectively testing different metal foil layers in the current collector, or by obtaining the corresponding metal foil layer after etching other metal foil layers in the current collector and then performing XRD tests.

[0127] In this application, nickel-based alloys refer to alloys whose main constituent element is nickel, and the mass content of Ni in nickel-based alloys generally exceeds 40%. Nickel-based alloys combine high tensile strength with good structural stability and material ductility, which is beneficial for balancing the strength and elongation at break of the current collector and improving the cycle life of the battery cell. It is understood that the alloy layer may include any one of solid solution, eutectoid, eutectic, or compound (intermetallic compound), or a combination of these.

[0128] In some embodiments, the nickel content in the nickel alloy layer is 40% to 90% by mass, and optionally 70% to 80%. As an example, the nickel content in the nickel alloy layer can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or any value between two of these.

[0129] Optionally, the mass content of the first metal element in the nickel-containing alloy layer is 10% to 60%, or optionally 15% to 35%; as an example, the mass content of the first metal element in the nickel-containing alloy layer can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, or any value range between the two.

[0130] In some embodiments, the mass content of nickel and the first metal element in the nickel-containing alloy layer is ≥95%, which can be 95%, 98%, 100%, or any value range between the two.

[0131] Furthermore, the nickel alloy layer also contains iron. Optionally, the nickel alloy layer comprises a nickel-iron-based alloy. Nickel-iron-based alloys exhibit high stability in electrochemical environments, are not easily corroded, and simultaneously possess high tensile strength and deformability, enabling the electrode to maintain high resistance to external shell pressure during cycling and retain high residual elongation at break after stretching.

[0132] Optionally, the iron content in the nickel alloy layer is 10% to 60% by mass, and for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any value between two of these. Optionally, the total mass content of iron and nickel in the nickel alloy layer is ≥95%, and can be 95%, 98%, 99%, 100%, or any value between two of these.

[0133] In some embodiments, the mass content of nickel is greater than the mass content of the other metal elements based on the total mass of the nickel-containing alloy layer. Further, the mass content of nickel in the nickel-containing alloy layer is greater than the mass content of the first metal element. In one example, the nickel-containing alloy layer is a nickel-iron alloy layer, in which the mass content of nickel is greater than the mass content of iron.

[0134] In some embodiments, the sheet resistance of the current collector is less than or equal to 15 mΩ / □, and can be selected from 2 mΩ / □ to 15 mΩ / □; as an example, the sheet resistance of the current collector can be 2 mΩ / □, 3 mΩ / □, 5 mΩ / □, 7 mΩ / □, 8 mΩ / □, 10 mΩ / □, 13 mΩ / □, 14 mΩ / □, 15 mΩ / □, or any value range between the two. This current collector has a low sheet resistance, which is beneficial for reducing the battery's drain-resistance (DCR) and improving battery heat generation.

[0135] Sheet resistance is essentially the resistance per unit square area of ​​a thin film or thin layer material. The test method is to use a sheet resistance meter probe to touch the foil surface, and the value read is the sheet resistance value.

[0136] In some embodiments, the tensile strength of the current collector is ≥1200 MPa, and can be selected from 1200 MPa to 2000 MPa. As an example, the tensile strength of the current collector can be selected from 1200 MPa, 1250 MPa, 1300 MPa, 1350 MPa, 1400 MPa, 1450 MPa, 1500 MPa, 1600 MPa, 1700 MPa, 1710 MPa, 1750 MPa, 1800 MPa, 1850 MPa, 1900 MPa, 1950 MPa, 2000 MPa, or any value within a range of two. In some embodiments, the tensile strength of the current collector is ≥1700 MPa, and can be selected from 1710 MPa to 2000 MPa.

[0137] The aforementioned current collector has high tensile strength, which increases the cumulative strain that the battery cell can withstand along its length, thus improving the cell's resistance to expansion, reducing the risk of electrode breakage, and improving the cycle life of the battery cell.

[0138] In some embodiments, the elongation at break of the current collector is ≥3%, and can be selected as 3% to 8%; as an example, the transverse elongation at break δ of the current collector can be 3%, 4%, 5%, 6%, 6.5%, 7%, 8%, 9% or any value range between the two.

[0139] By controlling the fracture elongation δ of the current collector within the above range, the possibility of stress concentration causing the current collector to fracture in the length direction is reduced, thereby reducing the fracture risk of the current collector and the electrode with the current collector, improving the overall tolerable cumulative strain of the battery cell, and improving the cycle life of the battery cell.

[0140] In this application, the tensile strength and elongation at break of the current collector at 25°C can be obtained by testing the tensile fracture curve of the current collector. The specific test method can be carried out in accordance with GB / T5230~1995 "Electrolytic Copper Foil" standard.

[0141] As an example, in this application, the test procedure for the tensile strength of the current collector at 25°C is as follows: The current collector is cut along its length to obtain at least four specimens with a length of 150±0.5 mm (the extension direction of this length is the same as the length direction of the current collector), a width of 15±0.25 mm, and a gauge length of 50±0.5 mm. If it is a wound electrode assembly, the length direction of the current collector refers to the winding direction of the current collector. The maximum tensile stress of the specimen during tensile fracture is taken as the tensile strength of the specimen, in MPa. The maximum tensile stress of the specimen is calculated by dividing the maximum load borne by the specimen during tensile fracture by the cross-sectional area of ​​the specimen. The cross-sectional area of ​​the specimen is calculated by multiplying the specimen width by the thickness, and the thickness of the specimen is measured using a micrometer. At least four specimens are tested, and the arithmetic mean is taken as the tensile strength of the current collector. The elongation at fracture is the ratio of the displacement at tensile fracture (i.e., the length of the specimen elongation) to the gauge length of the specimen. At least four specimens are tested, and the arithmetic mean is taken as the elongation at fracture.

[0142] In some embodiments, under test conditions of 25°C, the current collector withstands ≥3 bend cycles, optionally ranging from 3 to 10. The aforementioned high bend resistance of the current collector indicates good bend resistance, which helps improve the bend resistance of the electrode within the battery cell. Furthermore, improving the bend resistance of the current collector reduces the probability of battery failure due to breakage of the current collector within the highly bendable inner ring of the wound battery cell, thus improving the cycle life of the individual battery cells. In one example, the current collector withstands 5 to 6 bend cycles.

[0143] At 25°C, the current collector sample is folded 180° and then rolled back and forth at the fold with a 1.5Kg roller. After unfolding, observe whether cracking and light transmission occur at the fold. Record the number of times the fold cracks and light transmission occur. Test at least ten samples and take the arithmetic mean as the bending resistance of the negative electrode current collector.

[0144] One embodiment of this application provides a method for preparing a current collector, which can produce the above-mentioned current collector. The preparation method includes the following steps S10 to S20.

[0145] S10. Provide an anode, a first electroplating solution, and a cathode, perform a first electroplating process to form a nickel-containing alloy layer on the surface of the cathode; after the electroplating process, separate the nickel-containing alloy layer from the surface of the cathode.

[0146] The first electroplating solution includes a nickel source and a first metal source. The first metal element in the first metal source includes one or more of Fe, Zn, Ti, V, Cr, Mn, or Co. Understandably, during the first electroplating process in S10, the cathode rotates relative to the anode located in the electroplating solution, thereby forming a continuous nickel-containing alloy layer on the cathode.

[0147] S20. A second electroplating treatment is performed on the nickel-containing alloy layer using a second electroplating solution to form a metal layer on at least one side of the nickel-containing alloy layer; wherein the second electroplating solution includes a metal source and additives, and in the electroplating treatment to form the metal layer, the conveyor speed of the nickel-containing alloy layer is less than or equal to 3 m / min, the metal element of the metal source in the second electroplating solution includes one or more of Cu, Ni, Zn, and Cr, and the additives include one or more of sodium polydithiopropane sulfonate, sodium 3-mercapto-1-propane sulfonate, sodium thiazolinyl dithiopropane sulfonate, or dithiopropane sulfonic acid.

[0148] Understandably, in the second electroplating process of S20, the nickel-containing alloy layer serves as the deposition substrate for the metal layer. It moves relative to the electroplating solution along the length of the nickel-containing alloy layer, and the speed at which the nickel-containing alloy layer moves is called its conveyor speed. Understandably, the conveyor speed of the nickel-containing alloy layer is >0.

[0149] The above-mentioned method for preparing the current collector involves first electroplating to form a nickel-containing alloy layer, and then forming a metal layer on at least one side of the nickel-containing alloy layer. The additive contains both sulfonic acid groups and thio groups or mercapto groups. The sulfonic acid groups significantly reduce the surface tension of the plating solution, while the thio groups or mercapto groups can form complexes with metal ions, reducing the probability of disordered deposition. Furthermore, the additive does not contain long carbon chain groups, making it less prone to agglomeration in high-temperature plating solutions and exhibiting good stability. This promotes uniform distribution of metal ions and reduces the problem of uneven coating thickness caused by tip effects. Simultaneously, the second current collector is controlled... During the plating process, keeping the conveyor belt speed of the nickel alloy layer within the aforementioned smaller range reduces the splashing of the plating solution, preventing it from depositing on the conductive roller and forming a copper plating layer. This also lowers the risk of uneven deposition in different areas of the metal layer, resulting in better consistency in the amount of conductive metal material deposited on the nickel alloy layer. Furthermore, a slower conveyor belt speed means longer contact time between the deposition area and the plating solution, leading to more thorough deposition. This improves the uniformity of the metal layer thickness, resulting in a thickness variance of less than or equal to 0.5 μm. 2 The current collector prepared by this method is used in batteries. Thanks to the reduced sheet resistance of the current collector, the DC internal resistance (DCR) of the battery is significantly improved, thus enabling the battery to achieve both good cycle performance and a lower risk of thermal runaway.

[0150] If the conveyor speed of the nickel alloy layer is too high (greater than 3m / min), the splashing of the electroplating solution during the electroplating process will increase, resulting in more conductive metal material deposited on the outer areas of the nickel alloy layer, such as the cathode roller, and reducing the uniformity of the amount of conductive metal material deposited on the nickel alloy layer.

[0151] In some embodiments, the conveyor speed of the nickel alloy layer is 1 m / min to 3 m / min. Controlling the conveyor speed within this range can improve the thickness uniformity of the metal layer while maintaining high production efficiency. As an example, the conveyor speed of the nickel alloy layer is 1 m / min, 1.5 m / min, 2 m / min, 2.5 m / min, 3 m / min, or any value between two of these.

[0152] In some embodiments, in step S10, during the first electroplating process, the current density is 5 A / dm. 2 ~15A / dm 2 As an example, this current density could be 5 A / dm³. 2 8A / dm 2 10A / dm 2 12A / dm 2 15A / dm 2 Alternatively, any value within the range defined by any two of the above points as endpoints. Adjusting the current density within this range is beneficial for improving deposition efficiency.

[0153] Furthermore, in step S10, during the first electroplating process, the electroplating temperature is 50℃~60℃. Maintaining the temperature within this range helps to increase ion transport speed and improve deposition efficiency.

[0154] In some embodiments, during the first electroplating process, the surface roughness Ra of the cathode is 0.1 μm to 0.3 μm; as examples, it can be 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, or any value within the range defined by any two of the above points as endpoints. Adjusting the surface roughness Ra of the cathode to a minimum of 0.1 μm to 0.3 μm, i.e., adjusting the surface uniformity of the substrate forming the nickel alloy layer, is beneficial for improving the thickness uniformity of the nickel alloy layer; the thickness uniformity of the nickel alloy layer also affects the thickness uniformity of the metal layer, thus further improving the thickness uniformity of the metal layer.

[0155] In some embodiments, during the first electroplating process, the difference between the maximum and minimum distances between the anode and cathode roller surfaces is 0 to 1 cm. A smaller difference indicates a more parallel arrangement of the anode and cathode rollers, with the distances between them being approximately equal at all points. This improves the uniformity of the nickel-containing alloy layer along the length of the cathode roller. As an example, during the first electroplating process, the difference between the maximum and minimum distances between the anode and cathode roller surfaces is 0, 0.1 cm, 0.5 cm, 1 cm, or any value within a range defined by any two of the above points as endpoints.

[0156] In some of these embodiments, the nickel source comprises a divalent nickel salt.

[0157] Furthermore, the nickel source includes one or more of nickel sulfate, nickel chloride, or nickel carbonate. Nickel sulfate, for example, is NiSO4·6H2O.

[0158] In some embodiments, the first electroplating solution includes an Fe source. Optionally, the concentration of the Fe source in the first electroplating solution is 30 g / L to 80 g / L.

[0159] In some embodiments, the Fe source includes one or more of ferrous sulfate, ferrous chloride, or iron powder. Ferrous sulfate, for example, is FeSO4·7H2O.

[0160] In some embodiments, the first electroplating solution comprises nickel sulfate and ferrous sulfate.

[0161] Further, the concentration of the nickel source in the first electroplating solution is 200 g / L to 250 g / L. Further, the nickel source in the first electroplating solution includes one or more of nickel sulfate and nickel chloride; optionally, the concentration of nickel sulfate in the first electroplating solution is 140 g / L to 180 g / L, and the concentration of nickel chloride is 60 g / L to 80 g / L.

[0162] Optionally, the concentration of nickel sulfate in the first electroplating solution is 140 g / L to 180 g / L, the concentration of nickel chloride is 60 g / L to 80 g / L, and the concentration of ferrous sulfate is 30 g / L to 80 g / L.

[0163] In some embodiments, the first electroplating solution further includes one or more of a complexing agent and a brightener.

[0164] In some embodiments, the complexing agent includes one or more of sodium citrate, sodium gluconate, tartaric acid, or lactic acid. The main function of the complexing agent is to deposit the nickel and iron sources at the same potential, and the amount of complexing agent added affects the ratio of nickel to non-nickel metal elements in the nickel alloy layer. Further, the concentration of the complexing agent in the first electroplating solution is 20 g / L to 40 g / L; as an example, it is any value within the range of 20 g / L, 30 g / L, 40 g / L, or any two of the above points as endpoints.

[0165] In some embodiments, the brightener includes one or more of sodium saccharin, saccharin, 1,4-butynediol, butynediol diethoxy ether, polyethylene glycol, coumarin, formaldehyde, and pyridine derivatives. The brightener primarily functions to refine grains and level the foil, and the amount of brightener added affects the grain size of the nickel-based alloy. Higher brightener content results in smaller grain sizes and higher tensile strength of the nickel-iron foil; however, excessive brightener addition increases grain boundaries within the nickel-containing alloy layer, leading to uneven stress release within the grains, increasing the likelihood of microcracks and brittle fracture, and deteriorating the bending resistance of the nickel-based alloy. Controlling the brightener content within the aforementioned range allows the nickel-containing alloy layer to achieve both good tensile strength and bending resistance. Furthermore, in the first electroplating solution, the concentration of brightener is 1 g / L to 10 g / L. For example, it can be any value within the range of 1 g / L, 1.1 g / L, 1.5 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 9.5 g / L, 10 g / L, or any two of the above points as endpoints. It can be selected as 1.1 g / L to 10 g / L.

[0166] Further, the brightening agent includes one or more of primary brightening agents and secondary brightening agents. Optionally, the primary brightening agent includes one or more of saccharin and sodium saccharin. Optionally, the secondary brightening agent includes one or more of 1,4-butynediol, butynediol diethoxy ether, polyethylene glycol, coumarin, formaldehyde, and pyridine derivatives.

[0167] Furthermore, the brightener includes a primary brightener. In the first electroplating solution, the concentration of the primary brightener is 1 g / L to 10 g / L, and can be selected as 1 g / L to 9.5 g / L. As an example, it can be any value within the range formed by 1 g / L, 1.1 g / L, 1.5 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, 6 g / L, 7 g / L, 8 g / L, 9 g / L, 9.5 g / L, or any two of the above points as endpoints.

[0168] Furthermore, in the first electroplating solution, the brightener also includes a secondary brightener, the concentration of which is 0.01 g / L to 0.5 g / L. For example, it can be any value within the range of 0.01 g / L, 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, or any two of the above points as endpoints.

[0169] In some embodiments, the first electroplating solution may further include a conductive agent; optionally, the conductive agent includes one or more of sodium chloride, hydrochloric acid, or ammonium chloride. Optionally, the concentration of the conductive agent in the first electroplating solution is 10 g / L to 50 g / L, for example, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, or any value within the range defined by any two of the above points. The conductive agent can enhance ion transport capability and improve deposition efficiency.

[0170] In some embodiments, the first electroplating solution may further include a stabilizer; optionally, the stabilizer includes one or more of boric acid, citric acid, or fluoroborate. Optionally, the concentration of the stabilizer in the first electroplating solution is 20 g / L to 80 g / L, for example, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, or any value within the range defined by any two of the above points. The stabilizer's main function is to maintain pH stability and prevent excessive pH deviation due to the hydrogen evolution reaction, which would increase the degree of reaction polarization and thus affect the foil formation efficiency of the nickel alloy layer. Furthermore, during the formation of the nickel alloy layer, it can also lead to excessive deviation of the nickel content from the preset value and uneven formation of the solid solution phase.

[0171] In some embodiments, the first electroplating solution may further include an antioxidant; optionally, the antioxidant includes one or more of ascorbic acid, hydroxylamine sulfate, catechol, and hydroquinone. Optionally, the concentration of the antioxidant in the first electroplating solution is 1 g / L to 5 g / L, for example, 1 g / L, 2 g / L, 3 g / L, 4 g / L, 5 g / L, or any value within the range defined by any two of the above points. The main function of the antioxidant is to prevent air oxidation of the electroplating solution, for example, preventing the oxidation of ferrous ions in the first electroplating solution to ferric ions. Excessive ferric ion content will increase the number of defect vacancies in the nickel alloy layer, affecting grain boundary density and leading to a decrease in tensile strength and elongation.

[0172] In some embodiments, the first electroplating solution comprises: ferrous sulfate 30 g / L to 80 g / L, nickel sulfate 140 g / L to 180 g / L, nickel chloride 60 g / L to 80 g / L, conductive agent 10 g / L to 50 g / L, stabilizer 20 g / L to 60 g / L, primary brightener 1 g / L to 10 g / L, secondary brightener 0.01 g / L to 0.5 g / L, and complexing agent 20 g / L to 40 g / L.

[0173] Furthermore, the first electroplating solution comprises: ferrous sulfate 30 g / L~80 g / L, nickel sulfate 140 g / L~180 g / L, nickel chloride 60 g / L~80 g / L, sodium chloride 10 g / L~50 g / L, boric acid 20 g / L~60 g / L, sodium saccharin 1 g / L~10 g / L, 1,4-butynediol 0.01 g / L~0.5 g / L, and sodium citrate 20 g / L~40 g / L.

[0174] In some embodiments, in step S20, during the second electroplating process, the current density is 2 A / dm. 2 ~8A / dm 2 For example, it could be 2A / dm. 2 3A / dm 2 4A / dm 2 5A / dm 2 8A / dm 2 Or any value within the range formed by any two of the above points as endpoints. By controlling the tape speed of the nickel alloy layer in the second electroplating process within the aforementioned smaller range, and further controlling the current density in the second electroplating process within the aforementioned smaller range, the deposition rate of the metal layer is controlled to be slower, which is beneficial to improving the density of the grain arrangement and thus improving the uniformity of the metal layer thickness.

[0175] The metal source includes ions of one or more elements selected from Cu, Ni, Zn, and C. In some embodiments, the concentration of the metal source in the second electroplating solution is 80 g / L to 160 g / L, optionally 120 g / L to 140 g / L.

[0176] In some examples, the metal source in the second electroplating solution includes divalent copper ions.

[0177] Optionally, the Cu source includes one or more of copper sulfate, elemental copper, and copper chloride. Optionally, the components of the second electroplating solution include CuSO4·5H2O.

[0178] In some embodiments, the concentration of the additive in the second electroplating solution is 1 g / L to 5 g / L; as examples, it is any value within the range of 1 g / L, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, 3.5 g / L, 4 g / L, 4.5 g / L, 5 g / L, or any two of the above points as endpoints. Optionally, the concentration of sodium polydisulfide dipropane sulfonate in the second electroplating solution is 1 g / L to 5 g / L.

[0179] In some embodiments, the second electroplating solution further includes one or more of a brightener, a conductive agent, and a pH adjuster.

[0180] Furthermore, the brightener includes one or more of polyethylene glycol, tetrahydrothiazolium thione, and benzotriazole. Optionally, the concentration of the brightener in the second electroplating solution is 0.5 g / L to 3 g / L. The main function of the brightener is to refine the grains, thereby improving the tensile strength and elongation at break of the metal layer.

[0181] In some embodiments, the second electroplating solution further includes a conductive agent, which includes a chloride. Optionally, the chloride includes one or more of copper chloride or sodium chloride. Optionally, the concentration of the conductive agent in the second electroplating solution is 5 g / L to 25 g / L; as an example, it is any value within the range of 5 g / L, 8 g / L, 10 g / L, 15 g / L, 20 g / L, 25 g / L, or any two of the above points as endpoints. The conductive agent can enhance ion transport capability and improve deposition efficiency.

[0182] Further, the pH adjuster includes one or more of sulfuric acid and hydrochloric acid. Optionally, the concentration of the pH adjuster in the second electroplating solution is 20 g / L to 60 g / L. The function of the pH adjuster is to adjust the pH value and stabilize the acid-base balance of the electroplating solution. Further, the pH value of the second electroplating solution is less than 1.

[0183] Furthermore, the composition of the second electroplating solution includes: copper sulfate 80g / L~160g / L, sodium polydisulfide dipropane sulfonate 1g / L~5g / L, and copper chloride 5g / L~25g / L.

[0184] Furthermore, the electroplating temperature for the second electroplating treatment is 15℃~40℃. Temperature control within this range helps to increase ion transport speed and improve deposition efficiency.

[0185] One embodiment of this application provides a battery cell including an electrode assembly. The electrode assembly includes a positive electrode and a negative electrode. The negative electrode includes a negative current collector and a negative active layer disposed on at least one side of the negative current collector. The negative active layer includes a negative active material, and the negative current collector includes the current collector described above in this application.

[0186] Secondary batteries contain two main types of battery cells: stacked electrode assemblies and wound electrode assemblies. Wound electrode assemblies are widely used due to their ease of operation, high production speed, and high capacity. Compared to stacked electrode assemblies, wound electrode assemblies experience greater stress on the electrodes. This stress gradually accumulates, especially on the outer electrodes along the winding direction, which accelerates fracture and significantly degrades the cycle life of the wound cell towards the end of its cycle life. In some embodiments, the electrode assembly is a wound structure; in other words, it is a wound cell (or wound electrode assembly). The current collector's length direction is the same as the winding direction of the electrode assembly. Wound electrode assemblies include stacked and wound negative and positive electrode sheets. The wound electrode assembly has a negative electrode current collector containing the aforementioned current collector. Since nickel-containing alloy layers such as nickel-iron alloy foil have high tensile strength, they can better resist the expansion of the electrode sheet when used as a current collector. For example, when used as a negative electrode current collector, it can resist the expansion of high energy density negative electrode active materials such as silicon-based materials, reduce the cracking of the electrode sheet due to expansion, and improve the cycle performance of the battery.

[0187] A wound battery cell includes a corner area and a straight area. The straight area refers to the straight part formed after the positive and negative electrode plates and the separator are wound into a roll. It is the main working area of ​​the battery cell. The corner area refers to the arc-shaped part formed after the positive and negative electrode plates and the separator are wound into a roll.

[0188] Furthermore, the thickness of the wound battery cell is 10mm~50mm.

[0189] The thickness of the wound cell can be tested using any method known in the art. For example, a wound cell sample is placed on a flat surface, and the distance between the outermost flat areas is measured at the center of the sample using a micrometer. At least 10 wound cell samples are tested, and the arithmetic mean of the test results is taken as the thickness of the wound cell. It is understood that the wound cell sample can be a freshly prepared wound cell or a wound cell obtained from the disassembly of a single battery cell.

[0190] In some implementations, the thickness of the wound cell can be selected as 10mm, 15mm, 20mm, 25mm, 30mm, 35mm, 40mm, 45mm, 50mm or any value between the two.

[0191] Wound cells with thicknesses within the aforementioned range exhibit high energy density, but they also need to withstand high expansion forces during cycling, making the current collector prone to cracking and potentially leading to cell breakage and failure. The battery cell provided in this application uses the aforementioned current collector, which has superior tensile strength in the length direction, thereby reducing the risk of breakage of the current collector and the electrode sheet containing it, and improving the battery cell's resistance to expansion stresses. This allows for improved cycle life of the battery cell while maintaining high energy density.

[0192] In some implementations, the ratio of the length of the straight section to the length of the corner section of the wound cell is 1 to 10.

[0193] In some implementations, the ratio of the length of the straight section to the length of the corner section of the wound cell can be selected as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or any value range between the two.

[0194] The length of the straight section refers to the length of the straight portion formed by the positive and negative electrode plates and the separator in the wound cell along the length direction; the length of the winding section refers to the normal distance along the length direction from the intersection of the straight section and the winding section to the tangential surface at the farthest end of the winding section.

[0195] Battery cells with a straight section length to corner section length ratio within the aforementioned range have smaller corner radii. While this improves the space utilization of the battery casing, it also makes the inner ring of the cell prone to significant bending, leading to cracking of the inner ring electrode. The battery cells in this application embodiment are suitable for this cell design, achieving a balance between high energy density and cycle life.

[0196] Compared to stacked electrode assemblies, wound electrode assemblies experience greater stress on the electrodes. This stress gradually accumulates, particularly on the outer electrodes along the winding direction, accelerating breakage and significantly worsening the cycle life of the wound cell towards the end of its cycle life. Therefore, using the aforementioned current collector for the negative electrode of wound electrode assemblies can increase the overall tolerable cumulative strain of the battery cell, thereby reducing the risk of electrode breakage and improving the cycle life of the battery cell.

[0197] As a non-limiting example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0198] In some embodiments, the negative electrode further includes a negative electrode active layer disposed on at least one side of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material, which includes one or more of carbon-based materials and silicon-based materials. Carbon-based materials include, but are not limited to, graphite, and graphite includes, but is not limited to, one or more of artificial graphite and natural graphite. Further, silicon-based materials include one or more of elemental silicon, silicon-carbon materials, silicon-oxygen materials, silicon-nitrogen materials, and silicon alloys. Further, elemental silicon includes, but is not limited to, nano-silicon particles.

[0199] Furthermore, the negative electrode active material includes silicon-based materials. Silicon-based materials have high capacity, and using them as negative electrode active materials in secondary batteries is beneficial for improving the battery's energy density. However, silicon-based materials undergo significant volume changes during battery cycling, compressing the negative electrode current collector. If the current collector strength is low, it can easily lead to damage to the negative electrode current collector, thereby deteriorating the battery's cycle performance. In this application, the nickel alloy layer in the current collector has high strength, which can give the negative electrode current collector high tensile strength, reducing the risk of damage to the negative electrode current collector during battery cycling, and thus enabling the battery to maintain good cycle performance.

[0200] Furthermore, the mass content of silicon-based material in the negative electrode active material is ≥20%, and can be selected from 20% to 60%. As an example, based on the total mass of the negative electrode active layer, the mass content of silicon-based material can be selected as 20%, 25%, 30%, 40%, 50%, 60%, or any value range between the two.

[0201] Furthermore, the negative electrode active material includes a silicon-based material, and the mass content of silicon element is ≥10% based on the total mass of the negative electrode active layer, optionally 10%~20%. As an example, the mass content of silicon element based on the total mass of the negative electrode active layer can be 10%, 15%, 20%, or any value range between the two. Furthermore, the mass content of the silicon-based material in the negative electrode active material is 10%~20%, optionally 15%~20%.

[0202] Furthermore, the negative electrode active material includes carbon-based materials and silicon-based materials. Further, the silicon-based material has a mass content of 25% to 60% in the negative electrode active material, and examples include 25%, 30%, 35%, 40%, 50%, 55%, 60%, or any value range between two of these. Further, the carbon-based material or graphite has a mass content of 40% to 75% in the negative electrode active material. Examples include 40%, 50%, 55%, 60%, 65%, 70%, 75%, or any value range between two of these.

[0203] Based on the total mass of the negative electrode active layer, the mass content of silicon can be tested using any method known in the art. As an example, the cross-section of the negative electrode sheet is sliced, and the mass content of silicon in the cross-section of the negative electrode active layer is determined by a combination of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).

[0204] The aforementioned negative electrode current collector enhances the overall tolerance of cumulative strain of the battery cell, thereby reducing the risk of electrode breakage and improving the cycle life of the battery cell. Therefore, the battery cell of this application embodiment can be applied to high-silicon systems, which helps to further improve the energy density per unit mass of the battery cell.

[0205] In some embodiments, the negative electrode active layer may optionally include a binder. The binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0206] In some embodiments, the negative electrode active layer may optionally include a conductive agent. The conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0207] In some embodiments, the negative electrode active layer may also optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0208] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto at least one surface of the negative electrode current collector, and then obtaining the negative electrode sheet after processes such as drying and cold pressing. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector.

[0209] Another embodiment of this application provides a secondary battery, including the battery cell described above or the battery cell prepared by the above preparation method.

[0210] Another embodiment of this application provides an electrical device, including one or more of the above-described battery cell, the battery cell prepared by the above-described preparation method, and the above-described secondary battery.

[0211] The following description, with appropriate reference to the accompanying drawings, describes the battery cell, secondary battery, and electrical device of this application.

[0212] Typically, a battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. 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 while allowing ions to pass through.

[0213] The positive electrode, negative electrode, and separator are fabricated into an electrode assembly using a winding or stacking process. This electrode assembly is immersed in an electrolyte. Understandably, a single battery cell may include one or more electrode assemblies.

[0214] Positive electrode sheet

[0215] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0216] As a non-limiting example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0217] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymeric material substrate and a metal layer formed on at least one surface of the polymeric material substrate. The composite current collector can be obtained by forming a metal material on the polymeric material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limiting examples of the polymeric material substrate in the positive electrode current collector may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0218] In some embodiments, the positive electrode active layer includes a positive electrode active material, which includes lithium ions.

[0219] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more.

[0220] Non-limiting examples of lithium phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites. Further, the aforementioned carbon composites may be carbon-coated composites.

[0221] Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides (such as LiCoO2), lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their modified compounds.

[0222] Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.85 Co 0.10 Al 0.05 O2.

[0223] In some embodiments, the positive electrode active layer may optionally include a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0224] In some embodiments, the positive electrode active layer may optionally include a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0225] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry onto at least one surface of the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing, and other processes. The solvent can be selected from, but is not limited to, any of the solvents in the foregoing embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be a single surface of the positive electrode current collector or both surfaces of the positive electrode current collector.

[0226] electrolytes

[0227] Electrolytes function to conduct ions between the positive and negative electrode plates. This application does not impose any particular restrictions on the type of electrolyte; it can be selected according to requirements.

[0228] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0229] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0230] In some embodiments, the solvent includes one or more of ether solvents, ester solvents, and sulfone solvents.

[0231] As an example, the ether solvent may include one or more of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), and 1,3-dioxolane (DOL);

[0232] As an example, the ester solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propanesulfonate lactone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0233] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0234] In some embodiments, the additives in the electrolyte may include, but are not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), etc.

[0235] Separating membrane

[0236] In some embodiments, the battery cell also includes a separator disposed between the negative electrode and the positive electrode. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0237] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0238] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 12 μm to 20 μm.

[0239] In some embodiments, the negative electrode, the positive electrode, and the separator are wound together to form a wound electrode assembly, or stacked sequentially to form a stacked electrode assembly.

[0240] A secondary battery includes at least one battery cell. A secondary battery may include one or more battery cells.

[0241] In this application, unless otherwise specified, "battery cell" refers to the basic unit capable of converting chemical energy into electrical energy. Furthermore, a battery cell typically includes at least a positive electrode, a negative electrode, and an electrolyte. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of active ions between the positive and negative electrodes. A battery cell includes one or more electrode components, and an electrolyte is used to wet these electrode components.

[0242] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The image shows a single battery cell, which serves as an example of a square-structured battery cell.

[0243] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above. In some embodiments, the outer packaging of the battery cell may be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the battery cell may also be a flexible package, such as a pouch. The material of the flexible package may be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0244] In some of these embodiments, reference is made to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to actual needs.

[0245] In some embodiments, the secondary battery is a battery device. In some embodiments, the secondary battery includes one or more of a battery module and a battery pack. A battery module includes at least one battery cell. The number of battery cells contained in a battery module can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery module.

[0246] Figure 3 This is battery module 4 as an example. (See reference...) Figure 3In the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0247] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0248] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0249] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0250] In some embodiments, multiple battery cells 5 can also be arranged in any way in the battery box to directly obtain the battery pack 1.

[0251] In addition, one embodiment of this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Among them, mobile devices may be, for example, mobile phones, laptops, etc.; electric vehicles may be, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc., but are not limited to.

[0252] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0253] Figure 6 Here is an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of this electrical device for its secondary battery, the aforementioned battery pack or battery module can be used as the power source.

[0254] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can utilize the aforementioned battery cells as their power source.

[0255] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the application will be further described in detail below with reference to embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0256] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0257] Example 1

[0258] 1) Preparation of negative electrode current collector

[0259] 1.1 The nickel alloy layer (nickel-iron alloy foil layer) was prepared using an electroplating apparatus.

[0260] An electroplating apparatus is provided, comprising an anode, a first electroplating solution, and a cathode. The anode is a titanium mesh, and the cathode is a titanium roller. The titanium cathode roller is polished using a grinding wheel polisher to a surface roughness Ra of 0.1 μm, and then rinsed with deionized water. The cathode roller is installed in the electroplating apparatus, with the difference between the maximum and minimum distances between the anode and cathode roller surfaces being 0.5 cm. The electrolyte is injected into the electrolytic tank, circulated, and stirred, with the temperature controlled at 60°C.

[0261] Electroplating is performed to form a nickel-iron alloy foil layer on the surface of the cathode; after electroplating, the nickel-iron alloy foil layer is separated from the surface of the cathode.

[0262] The electroplating solution consists of: 40 g / L ferrous sulfate (iron source), 140 g / L nickel sulfate (nickel source), 60 g / L nickel chloride (nickel source), 30 g / L sodium chloride (conductive agent), 40 g / L boric acid (stabilizer), 1 g / L sodium saccharin (primary brightener), 0.5 g / L 1,4-butynediol (secondary brightener), and 40 g / L sodium citrate (complexing agent).

[0263] Electroplating parameters are: current density 8A / dm 2 The pH of the electroplating solution is 2.5.

[0264] A nickel-iron alloy foil layer is electroplated on a titanium roller, peeled off, and the thickness is 4μm. The peeled foil is then wound up.

[0265] 1.2 The metal layer (copper layer) is prepared using an electroplating apparatus.

[0266] The obtained nickel-iron alloy foil layer was subjected to double-sided copper plating. The copper plating solution formula was: 80 g / L copper sulfate, 4 g / L sodium polydisulfide dipropane sulfonate additive, and 5 g / L copper chloride.

[0267] The electroplating process is as follows: Nickel-iron alloy foil is passed through the electroplating tank, the conveyor roller speed is controlled at 1 m / min, and the copper plating current density is 3 A / dm², for double-sided copper plating. Finally, the foil is wound up to complete the electroplating.

[0268] A metal layer (copper layer) is formed by electroplating on both sides of a nickel-iron alloy foil layer. Both metal layers (copper layers) on both sides are 1μm thick. The resulting composite foil current collector includes a nickel-iron alloy foil layer and copper layers on both sides of the nickel-iron alloy foil layer, and is simply referred to as copper-plated nickel-iron foil.

[0269] Based on the total mass of the composite foil current collector, the mass content of Ni is 33.7%, the mass content of Fe is 29.1%, and the mass content of Cu is 38.2%.

[0270] Based on the total mass of the nickel-iron alloy foil layer, the mass content of Ni is 72%, the mass content of Fe is 26%, and the remainder is unavoidable impurities, with an average grain size of 47 nm.

[0271] The metal layer (copper layer) is a copper foil with a purity of over 99%, and the average grain size is 128 nm.

[0272] 2) Preparation of negative electrode sheet

[0273] The negative electrode active material (silicon carbon material and artificial graphite in a mass ratio of 30:70), thickener sodium carboxymethyl cellulose, binder styrene-butadiene rubber, and conductive agent acetylene black are mixed in a mass ratio of 92:1:5:2. Deionized water is added, and a negative electrode slurry is obtained under the action of a vacuum stirrer. The negative electrode slurry is uniformly coated on both sides of the composite foil current collector prepared in step 1). After drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0274] 3) Preparation of positive electrode sheet

[0275] LiNi, the positive electrode active material 0.9 Co 0.05 Mn 0.05 O2 (NCM) 811Conductive carbon black SP and binder PVDF are dispersed in solvent NMP at a weight ratio of 96:2:2 and mixed evenly to obtain positive electrode slurry; the positive electrode slurry is evenly coated on both sides of the positive electrode current collector aluminum foil, and then dried, cold-pressed and cut to obtain positive electrode sheet.

[0276] 4) Separating membrane

[0277] Polyethylene separator film is selected.

[0278] 5) Preparation of electrolyte

[0279] In an argon-atmospheric glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), ethylene carbonate (EC), methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Lithium salt LiPF6 was dissolved in the organic solvent, and fluoroethylene carbonate (FEC) was added as an additive to prepare an electrolyte solution with the following concentration: lithium salt concentration 1 mol / L, and FEC mass content in the electrolyte 5%.

[0280] 6) Battery manufacturing

[0281] The negative electrode, separator, positive electrode, and separator are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. After being wound into an electrode assembly, the assembly is placed in an outer package, electrolyte is injected, and the package is sealed. After processes such as standing, hot and cold pressing, formation, clamping, and capacity testing, the finished secondary battery cell is obtained.

[0282] Examples 2-3

[0283] The process is basically the same as in Example 1, except that the concentration of sodium polydithiopropane sulfonate, an additive, is different in the metal layer preparation process in step 1.2, as shown in Table 1.

[0284] Examples 4-5

[0285] The process is basically the same as in Example 3, except that the rotation speed and current density of the conveyor rollers for the nickel-iron alloy foil are different in step 1.2 of the metal layer preparation process, as shown in Table 1.

[0286] Comparative Example 1

[0287] The process is basically the same as in Example 1, except that the speed of the conveyor roller, the current density, and the type of additives are different in the preparation process of the nickel-iron alloy foil in step 1.2. Sodium dodecylbenzenesulfonate is used as the additive, as shown in Table 1.

[0288] The following are performance tests.

[0289] (1) Thickness and thickness variance test of nickel-iron alloy foil layer and metal layer in negative electrode current collector

[0290] Testing method for each layer thickness: Randomly select several (e.g., 10) 1cm × 1cm square samples from the negative electrode current collector. Place the samples on the test stage and bombard the sample surface with an argon ion beam to obtain a cross-sectional photograph of the current collector. Then, obtain the cross-sectional photograph and scale bar using a Zeiss scanning electron microscope. By comparing with the scale bar, randomly test several (e.g., 10) positions on each sample to obtain the thickness of the nickel-iron alloy foil layer and the metal layer at each position. In this way, obtain the thickness test values ​​of the nickel-iron alloy foil layer and the metal layer at each position in each sample (e.g., 100). Take the arithmetic mean of the thickness test values ​​of the nickel-iron alloy foil layer at each position (e.g., 100) as the thickness of the nickel-iron alloy foil layer in the negative electrode current collector. Take the arithmetic mean of the thickness test values ​​of the metal layer at each position (e.g., 100) as the thickness of the metal layer in the negative electrode current collector.

[0291] Calculation of metal layer thickness variance: The thickness variance of the nickel-iron alloy foil layer is calculated based on the thickness test values ​​of the nickel-iron alloy foil layer at each of the above locations (e.g., 100 locations).

[0292] The formula for calculating the variance of the above-mentioned metal layer thickness is as follows:

[0293] ;

[0294] in Xi is the arithmetic mean of the metal layer thickness test values, where Xi is the metal layer thickness test value at each location (e.g., 100 locations), Σ represents summation, and n is the number of test locations (e.g., 100 locations).

[0295] In the aforementioned Zeiss scanning electron microscope, elemental distribution maps of each layer were obtained using energy-dispersive X-ray spectroscopy. The elemental distribution map of the current collector prepared in Example 3 of this application is shown below. Figure 7 As shown.

[0296] (2) Sheet resistance test of negative electrode current collector

[0297] Sheet resistance is the resistance per square unit area of ​​the current collector. The test method is to use a sheet resistance meter probe to contact the foil surface and read the value as the sheet resistance value. Randomly test the sheet resistance of several (e.g., 10) different positions of the negative current collector and calculate their arithmetic mean, which is the sheet resistance of the negative current collector.

[0298] (3) Average grain size of nickel-iron alloy foil layer and metal layer in negative electrode current collector

[0299] The nickel-iron alloy foil layer or metal layer was used as the detection object. At 25℃, CuKα rays were used as the radiation source, with a scanning speed of 2º / min and a scanning range of 10º~100º. X-ray diffraction patterns were measured using an X-ray diffractometer. The peak with the highest diffraction intensity in the X-ray diffraction pattern was used as a reference. The average grain size was calculated using the Scherrer formula D=Kλ / (βcosθ), where D is the average grain size, K is the Scherrer constant (0.89), λ is the X-ray wavelength (selectable wavelength for testing is 0.154nm), β is the full width at half maximum (FWHM) of the diffraction peak, and θ is the diffraction angle.

[0300] (4) Tensile strength and elongation at break of the negative electrode current collector at 25℃

[0301] Cut at least four specimens of the negative electrode current collector, each with a length of 150±0.5 mm, a width of 15±0.25 mm, and a gauge length of 50±0.5 mm. The length direction of the specimens should be the same as the winding direction of the negative electrode current collector. The maximum tensile stress of the specimen during tensile fracture is taken as the tensile strength of the specimen, expressed in MPa. The maximum tensile stress of the specimen is calculated by dividing the maximum load borne by the specimen during tensile fracture by the cross-sectional area of ​​the specimen. The cross-sectional area of ​​the specimen is calculated by multiplying the specimen width by the thickness, and the thickness of the specimen is measured using a micrometer. The elongation at fracture is the ratio of the displacement at tensile fracture (i.e., the length of the specimen elongation) to the gauge length of the specimen. Test at least four specimens and take the arithmetic mean as the tensile strength and elongation at fracture of the negative electrode current collector.

[0302] The tensile testing machine operates at a speed of 50 mm / min, recording the instantaneous tensile force and displacement at the moment of fracture; strength = tensile force / 0.015 / substrate thickness, elongation = displacement / 50 mm.

[0303] (5) Bending resistance test of negative electrode current collector

[0304] At 25°C, the negative electrode current collector sample is folded 180° and then rolled back and forth at the fold with a 1.5Kg roller. After unfolding, it is observed whether cracking and light transmission occur at the fold. The number of times the rolling caused cracking and light transmission at the fold is recorded. At least ten samples are tested, and the arithmetic mean is taken as the bending resistance of the negative electrode current collector.

[0305] (6) Test the cycle performance of the battery.

[0306] The test method is as follows: The battery is charged at room temperature at a rate of 0.33C until the voltage equals 4.2V, then charged at a constant voltage to 0.05C, left to stand for 5 minutes, and then discharged at a rate of 0.33C until the voltage equals 2.8V. The reversible capacity is measured as C0. This charging and discharging process is repeated until the discharge capacity C of a certain cycle is reached. nRecord the total number of cycles until the battery level reaches 80% (C0). This total number of cycles indicates the battery's cycle life; a higher total number of cycles indicates a better cycle life. Where C... n This is the reversible capacity at the nth cycle, and the corresponding cycle number n is recorded as the cycle number. The results are shown in Table 1.

[0307] Table 1

[0308]

[0309] Table 1 shows that in Comparative Example 1, the excessively high tape speed in the copper plating process for the current collector resulted in a large thickness variance and sheet resistance of the current collector, leading to a high drain-resistance ratio (DCR) and poor cycle performance of the battery. In Examples 1-5, by adding additives and controlling the tape speed to less than or equal to 3 m / min, the copper plating process for the current collector resulted in a smaller thickness variance, lower sheet resistance, lower DCR, and improved cycle performance. Furthermore, the thickness variance of the metal layer was 0.02 μm. 2 ~0.2μm 2 Within this range, the current collector can achieve both low sheet resistance and high tensile strength.

[0310] 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.

[0311] The embodiments described above are merely illustrative of 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, and the specification and drawings can be used to interpret the scope of the claims.

Claims

1. A current collector, characterized in that, The device includes a nickel-containing alloy layer and a metal layer disposed on at least one side of the nickel-containing alloy layer. The nickel-containing alloy layer includes nickel and a first metal element other than nickel. The first metal element includes one or more of Fe, Zn, Ti, V, Cr, Mn, or Co. The metal layer includes one or more of Cu, Ni, Zn, and Cr. The thickness variance of the metal layer is less than or equal to 0.5 μm. 2 .

2. The current collector according to claim 1, characterized in that, It meets one or more of the following characteristics: (1) The thickness variance of the metal layer is 0.02 μm. 2 ~0.2μm 2 ; (2) The thickness of the metal layer is 0.5μm~2μm, and can be selected as 0.5μm~1μm; (3) Based on the total thickness of the current collector, the total thickness of the metal layer accounts for 10% to 40%.

3. The current collector according to any one of claims 1 to 2, characterized in that, The thickness of the nickel-containing alloy layer is 3μm to 8μm, and can be selected as 4μm to 6μm.

4. The current collector according to any one of claims 1 to 3, characterized in that, The sheet resistance of the current collector is less than or equal to 15 mΩ / □, and can be selected as 2 mΩ / □~15 mΩ / □.

5. The current collector according to any one of claims 1 to 4, characterized in that, The nickel content in the nickel alloy layer is 40% to 90%, and can be selected as 70% to 80%.

6. The current collector according to any one of claims 1 to 5, characterized in that, It meets one or more of the following characteristics: (1) The mass content of the first metallic element in the nickel-containing alloy layer is 10% to 60%, and can be selected as 15% to 35%; (2) The mass content of the nickel element and the first metal element in the nickel-containing alloy layer is ≥95%.

7. The current collector according to any one of claims 1 to 6, characterized in that, It meets one or more of the following characteristics: (1) The tensile strength of the current collector is ≥1700MPa, and can be selected as 1710MPa~2000MPa; (2) The elongation at break of the current collector is ≥3%, and can be selected as 3%~8%.

8. The current collector according to any one of claims 1 to 7, characterized in that, It meets one or more of the following characteristics: (1) The metal layer comprises a crystalline structure; optionally, the average grain size of the metal layer is 90nm~400nm, and optionally 100nm~300nm; (2) The nickel-containing alloy layer has a crystalline structure; optionally, the average grain size of the nickel-containing alloy layer is 10nm~80nm, and optionally 20nm~60nm.

9. A method for preparing a current collector, characterized in that, Includes the following steps: An anode, a first electroplating solution, and a cathode are provided for a first electroplating process to form a nickel-containing alloy layer on the surface of the cathode; after the electroplating process, the nickel-containing alloy layer is separated from the surface of the cathode. A second electroplating treatment is performed on the nickel alloy layer using a second electroplating solution to form a metal layer on at least one side of the nickel alloy layer. The first electroplating solution includes a nickel source and a first metal source. The first metal element in the first metal source includes one or more of Fe, Zn, Ti, V, Cr, Mn, or Co. The second electroplating solution includes a metal source and additives. In the electroplating process for forming the metal layer, the conveyor speed of the nickel alloy layer is less than or equal to 3 m / min. The metal element in the metal source of the second electroplating solution includes one or more of Cu, Ni, Zn, and Cr. The additives include one or more of sodium polydithiopropane sulfonate, sodium 3-mercapto-1-propane sulfonate, sodium thiazolinyl dithiopropane sulfonate, or dithiopropane sulfonic acid.

10. The method for preparing a current collector according to claim 9, characterized in that, It meets one or more of the following characteristics: (1) The concentration of the metal source in the second electroplating solution is 80 g / L to 160 g / L, and can be selected as 120 g / L to 140 g / L; (2) The concentration of the additive in the second electroplating solution is 1 g / L to 5 g / L; (3) The second electroplating solution further includes a conductive agent, which includes chloride. Optionally, the chloride includes one or more of copper chloride or sodium chloride. Optionally, the concentration of the conductive agent in the second electroplating solution is 5 g / L to 25 g / L. (4) In the second electroplating process, the current density is 2A / dm. 2 ~8A / dm 2 ; (5) In the second electroplating process, the conveying speed of the nickel alloy layer is 1m / min to 3m / min.

11. The method for preparing a current collector according to claim 9 or 10, characterized in that, It meets one or more of the following characteristics: (1) In the first electroplating process, the surface roughness Ra of the cathode is 0.1 μm to 0.3 μm; (2) In the first electroplating process, the current density is 5A / dm. 2 ~15A / dm 2 ; (3) In the first electroplating process, the difference between the maximum and minimum distance between the roller surface of the anode and the roller surface of the cathode is 0~1cm; (4) The concentration of the nickel source in the first electroplating solution is 200 g / L to 250 g / L; (5) The nickel source includes one or more of nickel sulfate, nickel chloride, or nickel carbonate; (6) The first metal source includes an Fe source, and the concentration of the Fe source in the first electroplating solution is 30 g / L to 80 g / L; (7) The first electroplating solution further includes a complexing agent, which includes one or more of sodium citrate, sodium gluconate, tartaric acid or lactic acid; optionally, the concentration of the complexing agent in the first electroplating solution is 20 g / L to 40 g / L. (8) The first electroplating solution further includes a brightener, which includes one or more of sodium saccharin, saccharin, 1,4-butynediol, butynediol diethoxy ether, polyethylene glycol, coumarin, formaldehyde and pyridine derivatives; optionally, the concentration of the brightener in the first electroplating solution is 1 g / L to 10 g / L. (9) The first electroplating solution further includes a conductive agent, which includes one or more of sodium chloride, hydrochloric acid or ammonium chloride; optionally, the concentration of the conductive agent in the first electroplating solution is 10 g / L to 50 g / L. (10) The first electroplating solution further includes a stabilizer, which includes one or more of boric acid, citric acid or fluoroborate; optionally, the concentration of the stabilizer in the electroplating solution is 20 g / L to 80 g / L.

12. A secondary battery, characterized in that, The current collector includes the current collector prepared by the preparation method of the current collector according to any one of claims 1 to 8 or any one of claims 9 to 11.

13. The secondary battery according to claim 12, characterized in that, The device includes an electrode assembly comprising a positive electrode and a negative electrode, wherein the negative electrode comprises a negative current collector and a negative active layer disposed on at least one side of the negative current collector, the negative active layer comprising a negative active material, and the negative current collector comprising the current collector according to any one of claims 1 to 8 or the current collector prepared by the preparation method according to any one of claims 9 to 11.

14. The secondary battery according to claim 13, characterized in that, It meets one or more of the following characteristics: (1) The electrode assembly is a wound structure, and the length direction of the current collector is the same as the winding direction of the electrode assembly; optionally, the thickness of the electrode assembly is 10mm~50mm; optionally, the electrode assembly includes a corner area and a straight area, and the ratio of the length of the straight area to the length of the corner area of ​​the electrode assembly is 1~10. (2) The negative electrode active material includes silicon-based material; optionally, the mass content of the silicon-based material in the negative electrode active layer is ≥20%, and can be 20%~60%.

15. An electrical appliance, characterized in that, The current collector includes the current collector prepared by the method of preparing the current collector according to any one of claims 1 to 8, the current collector according to any one of claims 9 to 11, or the secondary battery according to any one of claims 12 to 14.

Images