Current collector, method of manufacturing, secondary battery, and electric device

Abstract

The application provides a current collector, a preparation method thereof, a secondary battery and a power utilization device. The current collector comprises an alloy layer, the alloy layer comprises a nickel element and an iron element, the average grain size of the alloy layer is 15 nm to 60 nm, the alloy layer comprises a gamma solid solution phase and an alpha solid solution phase, the gamma solid solution phase comprises a (111) crystal face and a (200) crystal face, the alpha solid solution phase comprises a (110) crystal face and a (200) crystal face, and the percentage of the sum of the (111) crystal face and the (200) crystal face diffraction peak areas of the gamma solid solution phase to the sum of the (110) crystal face and the (200) crystal face diffraction peak areas of the alpha solid solution phase is 50% to 80%.

Description

[0001] Related applications

[0002] This application claims priority to Chinese Patent Application No. 2025101735709, 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, rechargeable batteries have been 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 cars, military equipment, aerospace, and many other fields. With the development of rechargeable batteries, their cycle performance needs further improvement. Summary of the Invention

[0005] The first aspect of this application provides a current collector comprising an alloy layer including nickel and iron elements, the alloy layer having an average grain size of 15 nm to 60 nm, the alloy layer comprising a γ solid solution phase and an α solid solution phase, wherein in the X-ray diffraction spectrum of the alloy layer, the γ solid solution phase comprises (111) and (200) crystal planes, and the α solid solution phase comprises (110) and (200) crystal planes; based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase is 50% to 80%.

[0006] In the aforementioned current collector, the average grain size of the alloy layer is 15nm~60nm, and the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase is 50%~80%, which allows the current collector to achieve both high tensile strength and good toughness. When this current collector is used in a secondary battery, it can maintain good structural stability and improve the battery's cycle performance. Therefore, the aforementioned current collector can achieve both high tensile strength and good toughness. After being assembled into a secondary battery, the current collector can withstand greater expansion forces while maintaining a stable structure, thereby improving the battery's cycle performance.

[0007] In some embodiments, the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase is 20% to 50%, based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the α solid solution phase.

[0008] In some embodiments, the ratio of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase to the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase is greater than or equal to 1.2, and optionally 2 to 4.

[0009] In some embodiments, the nickel element accounts for 50% to 85% of the mass percentage of the alloy layer.

[0010] In some embodiments, the iron element accounts for 15% to 50% of the mass percentage of the alloy layer.

[0011] In some embodiments, the alloy layer satisfies one or more of the following characteristics:

[0012] (1) Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the diffraction peak area of ​​the (111) crystal plane of the γ solid solution phase is 30%~50%;

[0013] (2) Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the diffraction peak area of ​​the (200) crystal plane of the γ solid solution phase is 20%~40%.

[0014] In some embodiments, the surface roughness Ra of the current collector is 20 nm to 120 nm.

[0015] In some implementations, the current collector satisfies one or more of the following characteristics:

[0016] (1) The transverse tensile strength of the current collector is greater than or equal to 1200 MPa, and optionally 1500 MPa to 2200 MPa;

[0017] (2) The transverse fracture elongation of the current collector is 2%~8%;

[0018] (3) The thickness of the current collector is 2μm~10μm.

[0019] In some embodiments, the current collector further includes a metal layer disposed on at least one side of the alloy layer; optionally, the metal layer includes one or more of Cu, Ni, Zn or Cr.

[0020] In some embodiments, the average grain size of the metal layer is larger than the average grain size of the alloy layer; optionally, the average grain size of the metal layer is 90nm~400nm, or optionally 100nm~300nm.

[0021] A second aspect of this application provides a method for preparing a current collector, comprising the following steps:

[0022] An insoluble anode, a first electroplating solution, and a cathode are provided for electroplating to form an alloy layer on the surface of the cathode; after the electroplating process, the alloy layer is separated from the surface of the cathode.

[0023] The first electroplating solution includes a nickel source, an iron source, a complexing agent, a first additive, and a second additive; the first additive includes one or more of saccharin, sodium saccharin, polyethylene glycol, polyethyleneimine, 1,4-butynediol, sodium naphthalene disulfonate, and formaldehyde; the second additive includes one or more of thiourea and its derivatives, and thiocyanate; in the first electroplating solution, the concentration of the iron source is 20 g / L to 80 g / L, and the concentration of the nickel source is 150 g / L to 250 g / L.

[0024] In some embodiments, the first electroplating solution satisfies one or more of the following characteristics:

[0025] (1) The concentration of the first additive is 3 g / L to 5 g / L;

[0026] (2) The concentration of the second additive is 0.1 g / L to 0.5 g / L.

[0027] In some embodiments, the first electroplating solution satisfies one or more of the following characteristics:

[0028] (1) The complexing agent includes one or more of citric acid, sodium citrate, sodium gluconate and gluconic acid;

[0029] (2) The first electroplating solution further includes an activator; optionally, the activator includes one or more of ammonium chloride and sodium chloride; optionally, the concentration of the activator is 10 g / L to 20 g / L;

[0030] (3) The first electroplating solution further includes a wetting agent; optionally, the wetting agent includes at least one of sodium dodecyl sulfate and sodium dodecyl sulfonate; optionally, the concentration of the wetting agent in the electroplating solution is 0.1 g / L to 0.5 g / L;

[0031] (4) The first electroplating solution further includes a conductive agent; optionally, the conductive agent includes at least one of sodium chloride, hydrochloric acid, and ammonium chloride; optionally, the concentration of the conductive agent in the electroplating solution is 10 g / L to 50 g / L.

[0032] (5) The first electroplating solution further includes a stabilizer; optionally, the stabilizer includes at least one of boric acid, citric acid, and fluoroborate; optionally, the concentration of the stabilizer in the electroplating solution is 20 g / L to 80 g / L;

[0033] (6) The first electroplating solution further includes an antioxidant; optionally, the antioxidant includes at least one 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.

[0034] (7) The pH value of the first electroplating solution is 2~3.

[0035] In some embodiments, the preparation method satisfies one or more of the following characteristics:

[0036] (1) The current density of the electroplating process is 6 A / dm. 2 ~8A / dm 2 ;

[0037] (2) The rotational speed of the cathode is 0.5 m / min to 0.8 m / min;

[0038] (3) The surface roughness Ra of the cathode is 100nm~200nm;

[0039] (4) The flow rate of the first electroplating solution is 50L / min~80L / min.

[0040] A third aspect of this application provides a secondary battery, including a current collector of the first aspect or a current collector prepared by the preparation method of the second aspect.

[0041] In some embodiments, the secondary battery includes a negative electrode sheet, the negative electrode sheet including the current collector and a negative electrode film layer located on at least one surface of the current collector; the negative electrode film layer includes a negative electrode active material, the negative electrode active material including a silicon-based material; optionally, the mass percentage of the silicon-based material in the negative electrode active material is greater than or equal to 20%, more preferably 30% to 60%.

[0042] In some embodiments, the secondary battery includes a wound electrode assembly, the wound electrode assembly including a negative electrode sheet, the negative electrode sheet including the current collector and a negative electrode film layer located on at least one surface of the current collector; the negative electrode film layer includes a negative electrode active material, the negative electrode active material including a silicon-based material; optionally, the mass percentage of the silicon-based material in the negative electrode active material is greater than or equal to 20%, more preferably 30% to 60%.

[0043] The fourth aspect of this application provides an electrical device, including the secondary battery of the third aspect. Attached Figure Description

[0044] 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:

[0045] Figure 1 This is a three-dimensional structural diagram of a secondary battery according to an embodiment of this application.

[0046] Figure 2 for Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0047] Figure 3 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.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1. Secondary battery; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. Detailed Implementation

[0050] To facilitate understanding of this application, a more comprehensive description will be provided below with reference to the accompanying drawings; however, some unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the scope of protection of this application.

[0051] 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 the specific range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently, 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 ​​1 and 2 are listed, and maximum range values ​​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 article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0052] In this application, unless otherwise specified, "about" means within a reasonable range above and below the stated number, and the range of fluctuation may vary depending on the type and value of the stated number. For example, a range of ±10%, ±5%, ±2%, ±1% is permissible. For instance, taking "about 20 degrees Celsius (abbreviated as: ℃)" and its approximation as ±1℃, approximate values ​​such as 19℃ and 19.5℃ within the approximation range indicated by "about 20℃" should also be included in the range indicated by "about 20℃".

[0053] In this application, the terms "multiple," "various," "several," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more. It is understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0054] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0055] In this application, the reference to "embodiment" means that a specific 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.

[0056] 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, but are preferably performed sequentially. For example, if method M 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, method M may also include step (c), meaning that step (c) can be added to method M in any order. For example, method M 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.

[0057] In this application, unless otherwise stated, “M, such as m1” means that m1 is a non-limiting example of M, and it can be understood that M is not limited to m1.

[0058] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0059] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. Any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" represents the group consisting of M, N, and "a combination of M and N". "Containing M and / or N" can mean "containing M, containing N, and containing both M and N", or "containing M, containing N, or containing both M and N", and can be appropriately understood according to the context.

[0060] The terms “combinations thereof,” “any combination thereof,” and “any combination thereof” as used in this application include all suitable combinations of any two or more of the listed items.

[0061] In this application, the term "suitable" in "suitable combination", "suitable method", "any suitable method", etc., refers to the technical solution that can implement this application.

[0062] In this application, terms such as "further," "even more," "especially," "for example," "as," "example," and "exemplary" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0063] In this application, the terms "first aspect," "second aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first aspect," "second aspect," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0064] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0065] In this application, the term "room temperature" generally refers to 4 degrees Celsius (abbreviated as ℃) to 35 degrees Celsius, and may refer to 20℃ ± 5℃. In some embodiments or examples of this application, room temperature refers to 20℃ to 30℃.

[0066] In this application, when a unit is specified for a data range, if the unit is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5 hours (abbreviated as h) or 3~5h both mean that the units for the left endpoint "3" and the right endpoint "5" are both h, and have the same meaning as 3h~5h. Furthermore, similar descriptions of other parameters such as temperature and size are interpreted in the same way.

[0067] In this application, the exemplary descriptions such as "in some implementations or embodiments" and "in one implementation or embodiment" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0068] In this application, unless otherwise specified, "secondary battery" refers to a basic unit capable of converting chemical energy into electrical energy, and typically includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode plates. The electrolyte acts as a conductor of active ions between the positive and negative electrode plates.

[0069] In some implementations, lithium-ion batteries can be either power batteries or energy storage batteries.

[0070] In rechargeable batteries, introducing a negative electrode active material with high specific capacity is beneficial to improving the battery's energy density. For example, silicon-based materials have high specific capacity, and introducing silicon-based materials into the negative electrode active material can effectively improve the battery's energy density. However, during battery cycling, silicon-based materials undergo significant volume changes, which subject the negative electrode current collector to substantial expansion forces, increasing the risk of breakage and thus deteriorating the battery's cycle performance.

[0071] Therefore, for batteries such as those with silicon-based materials, it is difficult to effectively balance energy density and cycle performance. However, as the above analysis shows, improving the stability of the negative electrode current collector, ensuring it maintains good structural stability even under the expansion force of silicon-based materials, is an effective method to achieve both high energy density and good cycle performance.

[0072] In the context of alloy layers, a grain refers to a tiny crystalline unit within the alloy, formed by the regular arrangement of atoms and possessing a specific crystal structure (such as the body-centered cubic structure of the α-solution phase and the face-centered cubic structure of the γ-solution phase). Grains are separated by grain boundaries, which are irregularly arranged atomic structures. Grain boundaries are the boundaries between different grains. Because adjacent grains have different crystal orientations, when a dislocation moves from one grain to another, it needs to change its direction of movement to adapt to the atomic arrangement orientation of the new grain. This process generates additional energy consumption, thus hindering dislocation movement.

[0073] Average grain size is a macroscopic statistical parameter that measures the overall size of grains within a nickel-iron alloy. When the average grain size decreases, the number of grain boundaries per unit volume increases, effectively creating more barriers that hinder dislocation movement within the alloy. According to the Hall-Page equation, as the average grain size decreases, the yield strength and tensile strength of the alloy increase accordingly.

[0074] Therefore, by refining the grain size of the alloy layer, the alloy can have higher tensile strength, laying the foundation for improving the structural stability of the current collector.

[0075] In their research on alloys containing nickel and iron, the inventors of this application discovered that when the average grain size of the alloy decreases to the nanometer scale, the alloy may experience uneven internal stress release due to excessive grain boundaries, leading to increased brittleness. Under external forces, the alloy is prone to brittle fracture, resulting in poor toughness. Therefore, for alloys containing nickel and iron, when the average grain size decreases to the nanometer scale, it is difficult to effectively balance tensile strength and toughness.

[0076] In response, the inventors conducted further research into how to achieve both high tensile strength and good toughness in alloys. In alloys containing nickel and iron, the γ solid solution phase, namely the face-centered cubic (FCC) solid solution, is the main stable phase of the alloy, with iron atoms forming a FCC lattice and nickel atoms dissolved within it. The atoms in the FCC cell structure are more closely packed, resulting in a higher packing density than the body-centered cubic (BCC) cell structure. Furthermore, the (111) plane in the FCC structure is both its close-packed plane and its slip plane. This means that during the plastic deformation of the foil layer, dislocations in the FCC structure are more likely to move on the (111) plane; because these planes have the highest atomic packing density, larger interplanar spacing, and relatively weaker atomic bonding forces between planes, resulting in less resistance during slip. This makes FCC materials more prone to plastic deformation rather than fracture under external force. Therefore, adjusting the γ solid solution phase in the alloy to have a higher γ solid solution phase is expected to improve the alloy's toughness.

[0077] However, the inventors discovered that increasing the volume percentage of the γ solid solution phase in the alloy layer leads to increased internal stress, which in turn increases the brittleness of the alloy layer, increasing the risk of brittle fracture of the current collector under external force. Conversely, a low volume percentage of the γ solid solution phase in the alloy layer results in weak atomic bonding, leading to a decrease in the tensile strength of the current collector and consequently affecting the cycle performance of the battery.

[0078] Based on this, this application provides a current collector including an alloy layer comprising nickel and iron elements, the alloy layer having an average grain size of 15 nm to 60 nm, and comprising a γ solid solution phase and an α solid solution phase. In the X-ray diffraction spectrum of the alloy layer, the γ solid solution phase comprises (111) and (200) crystal planes, and the α solid solution phase comprises (110) and (200) crystal planes. Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase is 50% to 80%.

[0079] In the aforementioned current collectors, by refining the alloy layer grains and combining them with an appropriate amount of γ solid solution phase, the current collectors can achieve both high tensile strength and good toughness.

[0080] In some embodiments, the average grain size of the alloy layer can be 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, or any value within the range of any two of the above values. For example, the average grain size of the alloy layer can be 15nm~50nm, 15nm~30nm, 20nm~60nm, 20nm~50nm, or 20nm~40nm.

[0081] It is understood that the γ solid solution phase includes the (111) and (200) crystal planes. Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase, the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase can represent the relative volume percentage of the γ solid solution phase in the alloy layer. The relative volume percentage of the γ solid solution phase represents the percentage of the volume of the γ solid solution phase relative to the sum of the volumes of the γ solid solution phase and the α solid solution phase.

[0082] It is understood that the α solid solution phase includes the (110) and (200) crystal planes. Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase, the percentage of the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase can represent the relative volume percentage of the α solid solution phase in the alloy layer. The relative volume percentage of the α solid solution phase represents the percentage of the volume of the α solid solution phase relative to the sum of the volumes of the γ solid solution phase and the α solid solution phase.

[0083] Optionally, the relative volume percentage of the γ solid solution phase in the alloy layer can be 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, or any value within the range of any two of the above values. For example, the relative volume percentage of the γ solid solution phase in the alloy layer can be 50%~70%, 55%~75%, or 60%~80%.

[0084] In some embodiments, the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase is 20% to 50%. This relative volume percentage of the α solid solution phase within this range can give the alloy layer better toughness, further reducing the risk of brittle cracking in the current collector and improving the cycle performance of the battery.

[0085] In this application, the test method for the volume percentage of γ-solution phase and α-solution phase in the alloy layer is as follows: 1. Obtain the target area sample by cutting the alloy layer along the thickness direction using wire cutting or abrasive wheel, and grind it with sandpaper up to 2000# to ensure a smooth surface. 2. Electrolyze the sample with an electrolyte of 10wt% perchloric acid and 90wt% ethanol at a voltage of 20-30V for 10-15 seconds to eliminate the mechanical damage layer and avoid pseudo-phase interference. 3. Place the sample in the center of the stage, clean it with alcohol, and compact it to ensure no residual impurities. 4. Perform X-ray diffraction (XRD) on the alloy layer using CuKα rays as the X-ray source. As an example, at 25℃, use CuKα rays as the X-ray source, scan at a scanning speed of 2º / min, and scan the range of 10º-100º; obtain the X-ray diffraction spectrum, and calculate the relative volume percentage of γ-solution phase and α-solution phase in the alloy layer by calculating the diffraction peak area ratio. For example, based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase, the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase can represent the relative volume percentage of the γ solid solution phase in the alloy layer.

[0086] In X-ray diffraction (XRD) spectra, the peak area of ​​a diffraction peak refers to the total area of ​​the peak above the background line, representing the integrated intensity. The integrated intensity of a diffraction peak of a certain phase is directly proportional to the volume percentage of the phase in the sample; therefore, the integrated intensity of the diffraction peak directly reflects the volume percentage of the phase in the compound. In practice, the peak area of ​​diffraction peaks is usually calculated directly by XRD analysis software, such as the "Calculate Peak Area" function in MDI JADE software. Thus, the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase, and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, can be obtained by integration calculation in the XRD spectra.

[0087] In the X-ray diffraction spectrum of the alloy layer, the peak position of the (111) crystal plane of the γ solid solution phase is 43.2±0.2°, the peak position of the (200) crystal plane of the γ solid solution phase is 51.7±0.3°, the peak position of the (110) crystal plane of the α solid solution phase is 44.7±0.2°, and the peak position of the (200) crystal plane of the α solid solution phase is 52.3±0.3°.

[0088] In some embodiments, the sum of the volume percentages of the γ-solution phase and the α-solution phase in the alloy layer is greater than or equal to 98%. In this case, the γ-solution phase and the α-solution phase constitute the majority of the alloy layer, while impurity phases, such as hard and brittle phases like carbides, are present in small quantities. This reduces the risk of these harmful phases becoming stress concentration sources, thereby reducing the risk of brittle fracture of the alloy layer under stress. Optionally, the sum of the volume percentages of the γ-solution phase and the α-solution phase in the alloy layer can be 98%, 98.2%, 98.5%, 98.8%, 99%, 99.2%, 99.5%, 99.8%, 99.9%, 100%, or any value within the range of any two of the above values. In the alloy layer, the sum of the volume percentages of the γ solid solution phase and the α solid solution phase refers to the ratio of the total area of ​​the diffraction peaks of the γ solid solution phase (111) and (200) crystal planes, and the sum of the diffraction peak areas of the α solid solution phase (110) and (200) crystal planes, based on the total area of ​​the diffraction peaks of the X-ray diffraction spectrum of the alloy layer.

[0089] In some embodiments, the ratio of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase to the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase is greater than or equal to 1.2. By controlling the volume ratio of the γ solid solution phase to the α solid solution phase, a better balance between tensile strength and toughness can be achieved, further reducing the risk of damage to the alloy layer under stress, and thus further improving the cycle performance of the battery. Optionally, the ratio of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase to the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase can be 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, or any value within the range of any two of the above values. Further, the ratio of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase to the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase is 1.2 to 4. Further optionally, the ratio of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase to the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase is 2 to 4.

[0090] In some embodiments, the alloy layer comprises a nickel-based alloy layer.

[0091] 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 can include any of the following: solid solution, eutectoid, eutectic, or compound (intermetallic compound), or a combination of these.

[0092] In some embodiments, the percentage of the diffraction peak area of ​​the (111) crystal plane of the γ solid solution phase is 30% to 50% based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase. For example, based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase, the percentage of the diffraction peak area of ​​the (111) crystal plane of the γ solid solution phase can be 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, or any value within the range of any two of the above values.

[0093] In some embodiments, the percentage of the diffraction peak area of ​​the (200) crystal plane of the γ solid solution phase is 20% to 40% based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase. Optionally, based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the (110) and (200) crystal planes of the α solid solution phase, the percentage of the diffraction peak area of ​​the (200) crystal plane of the γ solid solution phase can be 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, or any value within the range of any two of the above values.

[0094] In some embodiments, the mass percentage of nickel in the alloy layer is greater than the mass percentage of iron. A higher mass percentage of nickel in the alloy layer can result in higher tensile strength.

[0095] Optionally, in the alloy layer, nickel accounts for 50% to 85% of the alloy layer by mass. Optionally, the mass percentage of nickel in the alloy layer can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, or any value within the range of any two of the above values. For example, the mass percentage of nickel in the alloy layer can be 50% to 80%, 60% to 75%, or 50% to 70%.

[0096] Optionally, the iron element accounts for 15% to 50% of the mass of the alloy layer. Alternatively, the mass percentage of iron element in the alloy layer can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range of any two of the above values. For example, the mass percentage of iron element in the alloy layer can be 20% to 50%, 25% to 40%, or 30% to 50%.

[0097] In some embodiments, the sum of the mass percentages of nickel and iron in the alloy layer is ≥95%, which can be 95%, 96%, 97%, 98%, 99%, 100%, or any value within the range of any two of the above values.

[0098] In this application, the types of elements in the alloy layer can be tested using a scanning electron microscope (SEM) in conjunction with an energy-dispersive X-ray spectrometer (EDS). For example, the alloy layer sample is cleaned with alcohol, cut into small pieces, pasted onto conductive adhesive, placed in a vacuum chamber, and then the types of elements in the sample are tested using an energy-dispersive X-ray spectrometer.

[0099] In this application, the elemental content in the alloy layer can be tested by inductively coupled plasma spectroscopy (ICP). For example, a 0.5g sample of the alloy layer is wiped clean with alcohol, digested with a mixture of HCl and HNO3 in a volume ratio of 3:1, and then the elemental content is tested using ICP.

[0100] In some embodiments, the surface roughness Ra of the current collector is 20 nm to 120 nm. During battery cycling, volume changes in the active material may cause the active film layer to detach from the surface of the current collector, thereby deteriorating the battery's cycle performance. When the surface roughness Ra is above 20 nm, the current collector can maintain good adhesion to the active film layer, reducing the risk of the active film layer detaching from the current collector surface, which is beneficial for further improving the battery's cycle performance. When the surface roughness Ra is less than or equal to 120 nm, the impact of surface defects on the current collector's strength can be reduced, which is beneficial for maintaining a high tensile strength of the current collector, thereby further improving the battery's cycle performance.

[0101] It is understandable that the surface roughness Ra of the current collector represents the roughness Ra of the surface of the current collector used to support the active film layer.

[0102] Optionally, the surface roughness of the current collector can be 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, or any value within the range of any two of the above values. More preferably, the surface roughness of the negative electrode current collector is 30 nm to 100 nm.

[0103] In this application, the surface roughness Ra of the current collector can be tested using any method known in the art. For example, a 10cm × 10cm current collector sample is taken, the surface is wiped clean with alcohol, and then placed under an atomic force microscope. The Ra value is selected for testing, the test range is 10μm × 10μm, and the average value of the test values ​​in three different regions is selected as the surface roughness Ra of the negative electrode current collector.

[0104] It is understandable that the current collector sample can be obtained from a freshly prepared current collector or from a current collector obtained from disassembling a battery.

[0105] In some embodiments, the transverse tensile strength of the current collector is greater than or equal to 1200 MPa. In this application, by designing the alloy layer, the current collector can possess a high transverse tensile strength, enabling it to maintain good structural stability during battery cycling and further improving the battery's cycle performance. Optionally, the transverse tensile strength of the current collector can be 1200 MPa, 1300 MPa, 1400 MPa, 1500 MPa, 1600 MPa, 1700 MPa, 1710 MPa, 1730 MPa, 1750 MPa, 1800 MPa, 1850 MPa, 1900 MPa, 1950 MPa, 2000 MPa, 2050 MPa, 2100 MPa, 2150 MPa, 2200 MPa, or any value within the range of any two of the above values. Optionally, the transverse tensile strength of the current collector is 1500 MPa to 2200 MPa.

[0106] It is understood that the current collector includes both lateral and longitudinal directions. The lateral direction refers to the direction in which the current collector extends laterally, while the longitudinal direction refers to the direction perpendicular to the lateral direction of the current collector. The dimensions in the lateral direction are larger than those in the longitudinal direction.

[0107] It is understandable that, in the case of a secondary battery including an electrode assembly with a wound structure, the lateral direction of the current collector is the same as the winding direction of the current collector.

[0108] In this application, the transverse tensile strength of the current collector can be obtained by testing its tensile fracture curve. The specific testing method can be referenced in GB / T5230-1995 "Electrolytic Copper Foil" standard. As an example, at least four current collector specimens with a length of 200±0.5 mm (the extension direction of this length is the same as the transverse direction of the current collector), a width of 15±0.25 mm, and a gauge length of 50±0.5 mm are cut. The specimens are continuously loaded at 25℃ and a tensile speed of 50±0.5 mm / min until fracture. The maximum tensile stress of the specimen during the tensile fracture process 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 the tensile fracture process by the cross-sectional area of ​​the current collector. The cross-sectional area of ​​the current collector is calculated by multiplying the width by the thickness. The thickness of the current collector is measured using a micrometer, and the width of the current collector is the standard sample width of 15 mm. At least four current collector specimens are tested, and the average value is taken as the tensile strength of the current collector.

[0109] In some embodiments, the lateral elongation at break of the current collector is 2% to 8%. A higher lateral elongation at break reduces the risk of the current collector being crushed or broken, which is beneficial for further improving the cycle performance of the battery. Optionally, the lateral elongation at break of the current collector can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, or any value within the range of any two of the above values. More optionally, the elongation of the negative electrode current collector is 5% to 7%.

[0110] In this application, the transverse elongation at break of the current collector can be tested according to GB / T5230-1995 "Electrolytic Copper Foil" standard. As an example, at least four current collector samples with a length of 200±0.5 mm (the extension direction of this length is the same as the transverse direction of the negative electrode current collector), a width of 15±0.25 mm, and a gauge length of 50±0.5 mm are cut. The samples are continuously loaded at 25℃ and a tensile speed of 50±0.5 mm / min until fracture. The ratio of the displacement of the sample during the tensile fracture process to the gauge length of 50 mm is taken as the elongation at break of the negative electrode current collector. At least four current collector samples are tested, and the average value is taken as the elongation at break of the current collector.

[0111] In some embodiments, the thickness of the current collector is 2 μm to 10 μm. A thickness of 2 μm or more reduces the risk of breakage during battery application, helps maintain good structural stability, and further improves battery cycle performance. A thickness of less than 10 μm allows for a smaller current collector thickness, reducing its weight and thus promoting higher battery energy density. Optionally, the thickness of the current collector can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, or any value within the range of any two of these values. For example, the thickness of the negative electrode current collector can be 3 μm to 10 μm, 3 μm to 9 μm, 3 μm to 8 μm, 4 μm to 10 μm, 4 μm to 9 μm, or 4 μm to 8 μm.

[0112] In some embodiments, the current collector further includes a metal layer disposed on at least one side of the alloy layer; optionally, the metal layer includes one or more of Cu, Ni, Zn, or Cr. The metal layer has good electrical conductivity, which can improve the overall conductivity of the current collector, thereby increasing the conductivity of the electrode, reducing the DCR internal resistance of the battery, and thus improving the power performance of the battery.

[0113] In some embodiments, the metal layer includes Cu, with a Cu content of ≥99% by mass. The metal layer uses copper foil, which has high conductivity and low cost, which helps to further improve 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.

[0114] In some implementations, the metal layer comprises a crystalline structure.

[0115] In some embodiments, the average grain size of the metal layer is larger than that of the alloy layer. The alloy layer improves the tensile strength and elongation at break of the current collector through grain refinement; on this basis, the large-grain-size metal layer has good plastic deformation capability, which is beneficial to improving the toughness of the current collector. Under the synergistic effect of the multilayer structure of the current collector, the risk of battery failure due to current collector fracture is reduced.

[0116] Optionally, the average grain size of the metal layer is 90 nm to 400 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, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, or any value within the range of any two of the above values. 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~380nm, 100nm~350nm, 100nm~320nm, 100nm~300nm, 10 0nm~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, 110nm~150nm, etc.

[0117] In this application, the average grain size of the alloy layer or metal layer can be measured by X-ray diffraction (XRD). For example, X-ray diffraction (XRD) is performed on the alloy layer or metal layer in the current collector to analyze its average grain size. As an example, at 25°C, CuKα rays are used as the X-ray source, with a scanning speed of 2° / min and a scanning range of 10°-100°. X-ray diffraction patterns are measured using an X-ray diffractometer. The peak with the highest diffraction intensity in the X-ray diffraction pattern is used as a reference, and 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.

[0118] In some embodiments, the thickness of the alloy layer is 1 μm to 8 μm, and optionally 2 μm to 8 μm. As an example, the thickness of the alloy layer can be selected from 1 μm, 2 μm, 3 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 8 μm, and any value within the range of any two of the above values.

[0119] In some embodiments, the thickness of the alloy layer is 50% to 100% based on the total thickness of the current collector, and can be selected as 50% to 85%. Based on the total thickness of the current collector, the thickness of the alloy layer can be selected as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or any value within the range of any two of the above values.

[0120] In some embodiments, the thickness of the metal layer is 0.5 μm to 2 μm. As an example, the thickness of the metal layer can be selected from 0.5 μm, 1 μm, 1.5 μm, 2 μm, and any value within the range of any two of the above values.

[0121] In some implementations, the total thickness of the metal layer accounts for 15% to 50% of the total thickness of the current collector. As an example, the total thickness of the metal layer can be selected as 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value within the range of any two of the above values, based on the total thickness of the current collector.

[0122] 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.

[0123] The thickness of the current collector can be measured using any method known in the art; for example, it can be measured directly using a micrometer.

[0124] Another embodiment of this application provides a method for preparing a current collector, comprising the following steps:

[0125] S10: Provides an insoluble anode, a first electroplating solution, and a cathode for electroplating treatment to form an alloy layer on the surface of the cathode;

[0126] S20: After electroplating, the alloy layer is separated from the surface of the cathode;

[0127] The first electroplating solution includes a nickel source, an iron source, a complexing agent, a first additive, and a second additive. The first additive includes one or more of saccharin, sodium saccharin, polyethylene glycol, polyethyleneimine, 1,4-butynediol, sodium naphthalene disulfonate, and formaldehyde. The second additive includes one or more of thiourea and its derivatives, and thiocyanate. In the first electroplating solution, the concentration of the iron source is 20 g / L to 80 g / L, and the concentration of the nickel source is 150 g / L to 250 g / L.

[0128] Understandably, during the electroplating process, the cathode rotates relative to the anode located in the electroplating solution, thereby forming a continuous alloy layer on the cathode. Furthermore, the cathode is a cathode roller.

[0129] In the above-mentioned method for preparing current collectors, the use of iron and nickel sources can control the mass percentage of iron in the resulting alloy layer. The first additive can refine the average grain size of the alloy layer, making the interatomic arrangement more compact, increasing the volume percentage of the γ-solution phase in the alloy layer, and improving its strength. However, the use of the first additive increases grain boundary density, increasing the tortuosity between grains, making it difficult to release internal stress between grain boundaries, and increasing the risk of brittle fracture of the alloy foil. The second additive can adsorb onto the active sites of nickel-iron alloy crystal growth. The NH2 or SCN structure in the second additive can combine with metal ions to form an adsorption layer. This adsorption layer interferes with the uniform deposition of metal ions, resulting in a less compact microstructure of the coating, reducing grain boundary tortuosity, reducing the γ-phase, and ensuring that the volume percentage of the γ-solution phase in the resulting alloy layer is not too large. This, in turn, can reduce the internal stress of the alloy layer and reduce the risk of brittle fracture. Therefore, in the above-mentioned method for preparing current collectors, by using an iron source, a nickel source, and a specific second additive, the proportion of iron element and γ solid solution phase in the alloy layer can be controlled within a suitable range, so that the alloy layer can have both high tensile strength and good toughness.

[0130] Optionally, the concentration of the first additive is 3 g / L to 5 g / L. For example, the concentration of the first additive can be 3 g / L, 3.2 g / L, 3.5 g / L, 3.8 g / L, 4 g / L, 4.2 g / L, 4.5 g / L, 4.8 g / L, 5 g / L, or any value within the range of any two of the above values.

[0131] Optionally, the concentration of the second additive is 0.1 g / L to 0.5 g / L. For example, the concentration of the second additive can be 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, or any value within the range of any two of the above values.

[0132] In some embodiments, the first additive, a complexing agent, includes one or more of citric acid, sodium citrate, sodium gluconate, and gluconic acid. The complexing agent primarily functions to coordinate with metal ions in the electroplating solution, guiding their deposition on the cathode surface. The amount of complexing agent added affects the ratio of nickel to other metal elements in the nickel-based metal layer, thereby influencing the tensile strength of the nickel-based metal layer. Further, the concentration of the complexing agent in the first electroplating solution is 20 g / L to 60 g / L. For example, it can be 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, or any value within the range of any two of the above values.

[0133] In some embodiments, the first electroplating solution further includes an activator. Optionally, the activator includes one or more of ammonium chloride and sodium chloride. During the electroplating process, the second additive has a certain degree of inertness, and its use in conjunction with the activator can promote ion transport and improve production efficiency. Optionally, the concentration of the activator in the first electroplating solution is 10 g / L to 20 g / L. For example, the concentration of the activator can be 10 g / L, 11 g / L, 12 g / L, 13 g / L, 14 g / L, 15 g / L, 16 g / L, 17 g / L, 18 g / L, 19 g / L, 20 g / L, or any value within the range of any two of the above values.

[0134] In some embodiments, the first electrolyte may further include a wetting agent. Optionally, the wetting agent includes at least one of sodium dodecyl sulfate and sodium dodecyl sulfonate. Optionally, the concentration of the wetting agent in the first electroplating solution is 0.1 g / L to 0.5 g / L. For example, the concentration of the wetting agent can be 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, or any value within the range of any two of the above values.

[0135] In some embodiments, the first electroplating solution may further include a conductive agent. Optionally, the conductive agent includes at least one selected from sodium chloride, hydrochloric acid, and 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, and any value within the range of any two of the above values. The conductive agent can enhance ion transport capability and improve deposition efficiency.

[0136] In some embodiments, the first electroplating solution may further include a stabilizer. Optionally, the stabilizer includes at least one selected from boric acid, citric acid, and fluoroborate. Optionally, the concentration of the stabilizer in the 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, and any value within the range of any two of the above values. The main function of the stabilizer 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 alloy layer. Furthermore, during the formation of the alloy layer, it can also cause excessive deviation of the nickel content from the preset value and uneven formation of the solid solution phase.

[0137] In some embodiments, the first electroplating solution may further include an antioxidant. Optionally, the antioxidant includes at least one 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, and any value within the range of any two of the above values. The main function of the antioxidant is to prevent air oxidation of the electroplating solution, for example, to prevent ferrous ions in the electroplating solution from being oxidized to ferric ions. Excessive ferric ion content will increase the number of defect vacancies in the nickel-based metal layer, affecting the grain boundary density and leading to a decrease in tensile strength and elongation.

[0138] In some embodiments, the pH value of the first electroplating solution is 2 to 3.

[0139] In some embodiments, the nickel source includes at least one of nickel sulfate, nickel chloride, and nickel carbonate. Nickel sulfate, for example, is NiSO4·6H2O.

[0140] In some embodiments, the Fe source includes at least one of ferrous sulfate, ferrous chloride, and iron powder. Ferrous sulfate, for example, is FeSO4·7H2O.

[0141] In some embodiments, the first electroplating solution may optionally further include other metal sources besides nickel and iron, including one or more ions selected from W, Cr, Ag, Au, Pt, Nb, Mn, and Co.

[0142] Furthermore, other metal sources include at least one of W source, Cr source, Ag source, Au source, Pt source, Nb source, Mn source, and Co source.

[0143] In some implementations, the W source includes, but is not limited to, sodium tungstate.

[0144] In some implementations, the Cr source includes, but is not limited to, chromium sulfate.

[0145] In some implementations, the Mn source includes, but is not limited to, manganese sulfate.

[0146] Furthermore, in the first electroplating solution, the concentration of the iron source is 20 g / L to 80 g / L. For example, the concentration of the iron source can be 20 g / L, 25 g / L, 30 g / L, 35 g / L, 40 g / L, 45 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, or any value within the range of any two of the above values.

[0147] Furthermore, in the first electroplating solution, the concentration of the nickel source is 150 g / L to 250 g / L. For example, the concentration of the nickel source can be 150 g / L, 160 g / L, 170 g / L, 180 g / L, 190 g / L, 200 g / L, 210 g / L, 220 g / L, 230 g / L, 240 g / L, 250 g / L, or any value within the range of any two of the above values.

[0148] In some embodiments, the first electroplating solution comprises nickel sulfate and ferrous sulfate. Further, the concentration of ferrous sulfate in the electroplating solution is 20 g / L to 80 g / L. Further, the concentration of nickel sulfate in the first electroplating solution is 150 g / L to 250 g / L.

[0149] Furthermore, the composition of the first electroplating solution includes: ferrous sulfate 20g / L~80g / L, nickel sulfate 150g / L~200g / L, sodium saccharin 3g / L~5g / L, thiourea 0.1g / L~0.3g / L, ammonium chloride 10g / L~20g / L, sodium citrate 40g / L~80g / L, sodium dodecyl sulfate 0.1g / L~0.5g / L, and boric acid 40g / L~80g / L.

[0150] Furthermore, the electroplating temperature for forming the nickel-based metal layer is 50℃~60℃. Temperature control within this range helps to increase ion transport speed and improve deposition efficiency.

[0151] Furthermore, the current density for the electroplating process to form the nickel-based metal layer is 6 A / dm². 2 ~8A / dm 2 As an example, this current density could be 6 A / dm³. 2 7A / dm 2 8A / dm 2 And any value within the range formed by any two of the above values. Adjusting the current density within this range is beneficial for increasing the electroplating speed and improving deposition efficiency. Current density affects the deposition rate and lattice arrangement of metal ions. A current density of 6 A / dm³... 2 The above can enable metal atoms to arrange themselves in an orderly manner to form a dense lattice, which is beneficial to promoting the formation of the γ solid solution phase and adjusting the volume percentage of the γ solid solution phase in the alloy layer. The current density is 8 A / dm². 2 The following measures can reduce the risk of increased lattice defects caused by excessive current density.

[0152] Furthermore, the flow rate of the first electroplating solution is 50 L / min to 80 L / min; as an example, it can be any value within the range formed by 50 L / min, 60 L / min, 70 L / min, 80 L / min or any two of the above points as endpoints.

[0153] Furthermore, the rotational speed of the cathode roller is 0.5 m / min to 0.8 m / min; as an example, it can be 0.5 m / min, 0.6 m / min, 0.7 m / min, 0.8 m / min, or any value within the range of any two of the above values.

[0154] Furthermore, the surface roughness Ra of the cathode roller is 100 nm to 200 nm. Optionally, the surface roughness Ra of the cathode roller can be 100 nm, 150 nm, 200 nm, or any value within the range of any two of the above values.

[0155] In some embodiments, the anode is an insoluble anode. In this application, an "insoluble anode" refers to an anode that does not dissolve or dissolves very little when current passes through it. Its core function is to provide a platform for electron transfer, promoting the oxidation reaction of ions in the electroplating solution on its surface. Using an insoluble anode instead of a traditional soluble anode can reduce the problems of uneven foil thickness and coating contamination associated with soluble anodes. It also ensures good consistency in the thickness of the alloy layer in both the direction of the substrate travel and the direction perpendicular to the substrate travel, reducing the contamination of the plating solution and the coating by anode sludge.

[0156] Without limitation, the material of the insoluble anode includes titanium metal. Specifically, it can be, for example, a titanium metal mesh. Optionally, the surface of the insoluble anode can be provided with an anti-oxidation coating, the material of which is, for example, platinum, iridium-tantalum alloy, ruthenium-iridium alloy, rhodium, etc.

[0157] In some embodiments, the above preparation method includes step S30 after step S10 and before step S20: electroplating the nickel-based metal foil with a second electroplating solution to form a metal layer on at least one side of the alloy layer.

[0158] In some embodiments, the second electroplating solution contains a metal source, which includes ions of one or more elements selected from Cu, Ni, Zn, and Cr.

[0159] In some examples, the metal source in the second electroplating solution includes a Cu source. Further, the concentration of the Cu source in the second electroplating solution is 200 g / L to 250 g / L.

[0160] Optionally, the Cu source includes at least one of copper sulfate, elemental copper, and copper chloride. Optionally, the components of the second electroplating solution include CuSO4·5H2O.

[0161] Optionally, the second electroplating solution includes 200 g / L to 250 g / L of copper sulfate.

[0162] In some embodiments, the second electroplating solution further includes one or more of a brightener, a conductive agent, and a pH adjuster.

[0163] Furthermore, the brightener includes at least one of sodium polydisulfide dipropane sulfonate, tetrahydrothiazolium thione, and benzotriazole. Optionally, the concentration of the brightener in the second electroplating solution is 1 g / L to 3 g / L. The main function of the brightener is to refine the grains, thereby improving the tensile strength and elongation of the metal layer.

[0164] Furthermore, the second electroplating solution also includes a conductive agent, which includes chlorides. Optionally, the chloride includes one or more of copper chloride, sodium chloride, and hydrochloric acid. 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.

[0165] Further, the pH adjuster includes at least one 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.

[0166] As an example, the second electroplating solution, in addition to the metal source, also includes sulfuric acid and sodium polydisulfide dipropane sulfonate. Optionally, the second electroplating solution includes 200 g / L to 250 g / L copper sulfate, 20 g / L to 60 g / L sulfuric acid, and 1 g / L to 3 g / L sodium polydisulfide dipropane sulfonate.

[0167] 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.

[0168] Furthermore, the current density for forming the metal layer is 1 A / dm. 2 ~10A / dm 2 As an example, this current density could be 1 A / dm³. 2 2A / dm 2 3A / dm 2 4A / dm 2 5A / dm 2 8A / dm 2 10A / 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 and coating quality.

[0169] Another embodiment of this application provides a secondary battery, including the current collector described above or the current collector prepared by the method described above.

[0170] In some embodiments, the current collector described above or the current collector prepared by the above-described current collector preparation method is used as the negative electrode current collector of a secondary battery.

[0171] In some embodiments, the secondary battery includes a negative electrode sheet, which includes a current collector and a negative electrode film layer located on at least one surface of the current collector; the negative electrode film layer includes a negative electrode active material, which includes a silicon-based material. Optionally, the mass percentage of the silicon-based material in the negative electrode active material is greater than or equal to 20%. For example, the mass percentage of the silicon-based material in the negative electrode active material can be 20%, 30%, 40%, 50%, 60%, 70%, or any value within the range of any two of the above values. More optionally, the mass percentage of the silicon-based material in the negative electrode active material is 30% to 60%.

[0172] In some embodiments, the secondary battery includes a wound electrode assembly, which includes a negative electrode sheet. The negative electrode sheet includes a current collector and a negative electrode film layer located on at least one surface of the current collector. The negative electrode film layer includes a negative electrode active material, which includes a silicon-based material. Optionally, the mass percentage of the silicon-based material in the negative electrode active material is greater than or equal to 20%. For example, the mass percentage of the silicon-based material in the negative electrode active material can be 20%, 30%, 40%, 50%, 60%, 70%, or any value within the range of any two of the above values. Further optionally, the mass percentage of the silicon-based material in the negative electrode active material is 30% to 60%.

[0173] For secondary batteries with a wound structure, the volume change of the silicon-based material during cycling subjectes the negative electrode current collector to significant expansion forces, increasing the risk of damage. Furthermore, due to side reactions, the electrode becomes increasingly thicker, leading to greater expansion forces. Since the outer ring of the wound structure already experiences the greatest force, the increased expansion forces from the silicon-based material result in even greater forces on the outer ring. Therefore, the outer ring of the wound structure is more prone to breakage, deteriorating the battery's cycle performance. In this application, the negative electrode current collector exhibits better structural stability, effectively reducing the risk of breakage of the outer ring of the wound structure and improving the battery's cycle performance.

[0174] The secondary batteries described in some embodiments of this application are applicable to high-silicon systems, which helps to further improve the energy density of the batteries.

[0175] It is understood that silicon-based materials include one or more of silicon-carbon composites and silicon oxides.

[0176] In some embodiments, the negative electrode active material further includes a carbon-based material. Optionally, the carbon-based material includes one or more of graphite, soft carbon, and hard carbon.

[0177] In some embodiments, the carbon-based material accounts for 0% to 80% of the mass of the negative electrode active material. For example, the mass percentage of the carbon-based material in the negative electrode active material can be 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 0, or any value within the range of any two of the above values.

[0178] In some embodiments, the negative electrode active material accounts for 91% to 98% of the mass of the negative electrode film. For example, the mass percentage of the negative electrode active material in the negative electrode film can be 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, or any value within the range of any two of the above values.

[0179] In some embodiments, the negative electrode film 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). Optionally, the binder accounts for 1% to 5% of the mass percentage of the negative electrode film layer. Optionally, the mass percentage of the binder in the negative electrode film layer may be 1%, 2%, 3%, 4%, 5%, or any value within the range of any two of the above values.

[0180] In some embodiments, the negative electrode film 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. Optionally, the conductive agent accounts for 0.2% to 2% of the mass percentage of the negative electrode film layer. Optionally, the conductive agent accounts for 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, and any value within the range of any two of the above values.

[0181] In some embodiments, the negative electrode film may optionally include other additives, such as a thickener. The thickener may be sodium carboxymethyl cellulose (CMC-Na). Optionally, the thickener accounts for 0.8% to 2% of the mass of the negative electrode film. Optionally, the mass percentage of the thickener in the negative electrode film may be 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0182] 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 to form a negative electrode slurry. Optionally, a non-limiting example of a solvent is deionized water. The negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after processes such as drying and cold pressing, the negative electrode sheet is obtained. 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.

[0183] In some embodiments, the density of the negative electrode sheet on one side is 3 mg / cm³. 2 ~10mg / cm 2 Optionally, the density of the negative electrode sheet on one side can be 3 mg / cm³. 2 4mg / cm 2 5mg / cm 2 6mg / cm 2 7mg / cm 2 8mg / cm 2 9mg / cm 2 10mg / cm 2 And any value within the range consisting of any two of the above values.

[0184] In this application, the unilateral density of the electrode sheet has a well-known meaning in the art and can be tested using methods known in the art. For example, the battery is placed in a 25°C oven and left to stand for 2 hours. Once the battery temperature is maintained at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.0V. The battery is then disassembled to obtain the electrode sheet, which is cut into small circular pieces with an area of ​​S1. The mass of these pieces is weighed and recorded as M1. Then, the film layer of the weighed electrode sheet is removed, and the weight of the current collector is weighed and recorded as M0. The unilateral density of a single-sided coated electrode sheet is (M1-M0) / S1, and the unilateral density of a double-sided coated electrode sheet is (M1-M0) / (2×S1). To ensure the accuracy of the test results, multiple sets can be tested, such as 10 sets of samples, and the average value is calculated as the test result.

[0185] In some embodiments, the compaction density of the negative electrode sheet is 0.9 g / cm³. 3 ~1.6g / cm 3 Optionally, the compaction density of the negative electrode sheet can be 0.9 g / cm³. 3 1g / cm 3 1.1g / cm 3 1.2g / cm 3 1.3g / cm 3 1.4g / cm 3 1.5g / cm 31.6g / cm 3 And any value within the range consisting of any two of the above values.

[0186] In this application, the compaction density of the electrode sheet can be tested using methods known in the art. As an example, the battery is placed in a 25°C oven environment and left to stand for 2 hours. After the battery temperature is maintained at 25°C, the battery is discharged at a constant current of 1 / 3C to 2.0V. The battery is then disassembled to obtain the electrode sheet, which is cut into small circular pieces with an area of ​​S. The mass of the circular pieces is W1, and the thickness T1 of the electrode sheet is measured using a micrometer. Then, the film layer of the electrode sheet after weighing is wiped off, the mass of the current collector is weighed and recorded as W2, and the thickness T2 of the current collector is measured using a micrometer. The compaction density of the electrode sheet is then PD = (W1-W2) / [(T1-T2)×S].

[0187] In some embodiments, the positive electrode includes a positive current collector and a positive active layer located on at least one surface of the positive current collector. The positive active material of the positive active layer includes one or more of lithium-containing transition metal oxides and lithium-rich manganese-based materials. Lithium-containing transition metal oxides and lithium-rich manganese-based materials have higher capacity, which is beneficial for improving the energy density of the battery.

[0188] In some embodiments, the chemical formula of the lithium transition metal oxide is Li. x (Ni a Co b Mn c ) 1-d M d O 2-y A y Wherein, 0.2≤x≤1.2, 0.2≤a≤1, 0≤b≤1, 0≤c≤1, a+b+c=1, 0≤d<1, 0≤y<2, M includes one or more of Zr, Sr, B, Sn, Al, Mg, Fe, Cu, V, Ti, Zr, W, Sb, Dy and Te, and A includes one or more of N, P, S and halogen elements.

[0189] Understandably, 'a' is typically used to represent the nickel content in lithium-containing transition metal oxides. A larger 'a' indicates a higher nickel content, while a smaller 'a' indicates a lower nickel content. As some possible examples of 'a', 'a' can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.82, 0.85, 0.88, 0.9, 0.92, 0.95, 0.98, 1, and any value within the range of any two of the above values. Optionally, 'a' ≥ 0.8.

[0190] Understandably, 'b' is typically used to represent the cobalt content in lithium-containing transition metal oxides. A larger 'b' indicates a higher cobalt content, while a smaller 'b' indicates a lower cobalt content. As some possible examples of 'b', it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and any value within the range of any two of the above values.

[0191] Understandably, 'c' is typically used to represent the manganese content in lithium-containing transition metal oxides. A larger 'c' indicates a higher manganese content, while a smaller 'c' indicates a lower manganese content. As some possible examples of 'c', it can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, and any value within the range of any two of the above values.

[0192] Understandably, d is typically used to represent the content of element M in lithium-containing transition metal oxides. A larger d indicates a higher content of element M, while a smaller d indicates a lower content of element M. As some possible examples of d, d can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and any value within the range of any two of the above values. Optionally, 0 ≤ d ≤ 0.05.

[0193] Understandably, x is typically used to represent the lithium content in lithium-containing transition metal oxides. A larger x indicates a higher lithium content, while a smaller x indicates a lower lithium content. As some possible examples of x, x can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, and any value within the range of any two of the above values.

[0194] Understandably, y is typically used to represent the content of element A in lithium-containing transition metal oxides. A larger y indicates a higher content of element A, while a smaller y indicates a lower content of element A. As some possible examples of y, y can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, and any value within the range of any two of the above values. Optionally, 0 ≤ y ≤ 0.05.

[0195] It is understandable that A includes one or more of N, P, S and halogen elements, where halogen elements can be F, Cl, Br, etc.

[0196] Optionally, the lithium-containing transition metal oxide includes LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.25 Mn 0.25 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.9 Co 0.09 Mn 0.01 O2, LiNi 0.92 Co 0.05 Mn 0.03 O2, LiNi 0.96 Co 0.02 Mn 0.02 O2, LiNi 0.85 Co 0.1 Al 0.05 O2, etc.

[0197] In some embodiments, lithium-rich manganese-based materials include those with the chemical formula nLi₂MnO₃•(1-n)Li x1 Ni x2 Mn x3 M1 x4 O 2-x5Wherein, 0.1≤n≤0.3, 0.2≤x1≤1.2, 0.3≤x2<1, 0<x3≤0.7, 0≤x4≤0.1, 0≤x5≤0.2, and M1 includes one or more of Na, Mg, Al, Ca, Ba, V, Zn, Ti, Fe, Co, Cr, Nb, W, Mo, Zr, Ta, and Hf.

[0198] Optionally, in lithium-rich manganese-based materials, n can be 0.1, 0.12, 0.15, 0.18, 0.2, 0.22, 0.25, 0.28, 0.3, or any value within the range of any two of the above values.

[0199] In lithium-rich manganese-based materials, as some optional examples of x1, x1 can be 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, and any value within the range consisting of any two of the above values.

[0200] As some alternative examples of x2, x2 can be 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, 0.99, and any value within the range consisting of any two of the above values.

[0201] As some alternative examples of x3, x3 can be 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and any value within the range consisting of any two of the above values.

[0202] As some alternative examples of x4, x4 can be 0, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and any value within the range consisting of any two of the above values.

[0203] As some alternative examples of x5, x5 can be 0, 0.01, 0.02, 0.05, 0.08, 0.1, 0.12, 0.15, 0.18, 0.2, and any value within the range consisting of any two of the above values.

[0204] In some embodiments, the positive electrode active material may also include a lithium phosphate with an olivine structure.

[0205] In some embodiments, lithium-containing phosphates may include at least one of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon. Lithium-containing phosphates may also include one or more of lithium manganese phosphate and a composite of lithium manganese phosphate and carbon.

[0206] In some embodiments, the positive electrode active material may further include one or more of the following materials: lithium cobalt oxide, lithium manganese oxide, lithium manganese cobalt oxide, and modified compounds thereof. Non-limiting examples of lithium cobalt oxide may include LiCoO2. Non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.

[0207] In some embodiments, the density of the positive electrode sheet on one side is 200 mg / 1540.25 mm. 2 ~600mg / 1540.25mm 2 For example, the density of a single side of the positive electrode sheet can be 200mg / 1540.25mm². 2 250mg / 1540.25mm 2 300mg / 1540.25mm 2 350mg / 1540.25mm 2 400mg / 1540.25mm 2 450mg / 1540.25mm 2 500mg / 1540.25mm 2 550mg / 1540.25mm 2 600mg / 1540.25mm 2 And any value within the range consisting of any two of the above values.

[0208] In some embodiments, the compaction density of the positive electrode sheet is 3.2 g / cm³. 3 ~3.8g / cm 3 For example, the compaction density of the positive electrode sheet can be 3.2 g / cm³. 3 3.3g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 3.8g / cm 3 And any value within the range consisting of any two of the above values.

[0209] 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. Optionally, the binder accounts for 0.7% to 3% of the mass percentage of the positive electrode active layer. For example, the binder percentage of the positive electrode active layer may be 0.7%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or any value within the range of any two of the above values.

[0210] 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. Optionally, the conductive agent accounts for 0.8% to 2% of the mass percentage of the positive electrode active layer. For example, the mass percentage of the conductive agent in the positive electrode active layer may be 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.8%, 2%, or any value within the range of any two of the above values.

[0211] 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 polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be obtained by forming a metal material on a polymer 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 polymer 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).

[0212] 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 electrode 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 described 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.

[0213] It is understood that a secondary battery may also include a separator. The separator is located between the positive electrode and the negative electrode. This application does not impose any particular limitation on the type of separator; any well-known porous separator with good chemical and mechanical stability can be selected.

[0214] 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.

[0215] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0216] In some embodiments, the secondary battery also includes an electrolyte. The electrolyte serves to conduct ions between the positive and negative electrodes. This application does not impose any particular limitation on the type of electrolyte, which can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or entirely solid-state.

[0217] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0218] 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 bisfluorosulfonylimide (LiFSI), lithium bistrifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0219] In some embodiments, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate, fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0220] 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 functional 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.

[0221] 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), and trifluoromethyl ethylene carbonate (TFPC).

[0222] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0223] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0224] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. The material of the soft pack can be plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0225] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 1.

[0226] In some implementations, refer to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The secondary battery 1 may contain one or more electrode assemblies 12, which can be selected by those skilled in the art according to actual needs.

[0227] In some implementations, the secondary battery may be a lithium-ion battery.

[0228] In some implementations, the secondary battery can be a single battery cell, a battery module, or a battery pack.

[0229] The battery module includes at least one secondary battery. The number of secondary batteries in the battery module can be one or more, and those skilled in the art can select an appropriate number based on the application and capacity of the battery module.

[0230] In a battery module, multiple secondary batteries can be arranged sequentially along the length of the module. Alternatively, they can be arranged in any other manner. Furthermore, these multiple secondary batteries can be secured using fasteners.

[0231] Optionally, the battery module may also include a housing with a receiving space in which multiple secondary batteries are housed.

[0232] In some embodiments, the battery modules 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.

[0233] The battery pack may include a battery box and multiple battery modules disposed within the battery box. The battery box includes an upper body and a lower body, with the upper body covering the lower body to form a closed space for accommodating the battery modules. The multiple battery modules can be arranged in any manner within the battery box.

[0234] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The battery can be used as a power source for the electrical device or as an 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.

[0235] As an electrical device, a rechargeable battery can be selected based on its usage requirements.

[0236] Figure 3 Here is an example of an electrical device 2. 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, a battery pack or battery module can be used.

[0237] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can be powered by a battery.

[0238] 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.

[0239] 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.

[0240] Example 1

[0241] (1) Preparation of negative electrode current collector

[0242] 1.1 The alloy layer was prepared using an electroplating apparatus.

[0243] The electroplating apparatus includes an anode, a first electroplating solution, and a cathode. The anode is a titanium mesh, and the cathode is a titanium roller with a ruthenium-iridium alloy coating on its surface. The first electroplating solution consists of: 30 g / L ferrous sulfate (Fe source), 200 g / L nickel sulfate (Ni source), 30 g / L sodium citrate (complexing agent), 3 g / L sodium saccharin (first additive), 3 g / L thiourea (second additive), 15 g / L ammonium chloride (activator), 20 g / L sodium chloride (conductive agent), 40 g / L boric acid (stabilizer), and water as the solvent.

[0244] Electroplating parameters are: current density 6A / dm 2 The temperature was 50℃, the cathode rotation speed was 0.5 m / min, the pH of the first electroplating solution was 2.5, and the flow rate of the first electroplating solution was 50 L / min.

[0245] An alloy layer is formed by electroplating on a titanium roller, and then the alloy layer is peeled off from the titanium roller. The thickness of the alloy layer is 4μm.

[0246] 1.2 The metal layer (copper layer) is prepared using an electroplating apparatus.

[0247] The electroplating apparatus includes an anode, a second electroplating solution, and a cathode. The anode is a titanium mesh with a ruthenium-iridium alloy coating on its surface, the cathode is an alloy layer, and the second electroplating solution consists of: 200 g / L copper sulfate, 30 g / L sulfuric acid, 1.2 g / L sodium polydisulfide dipropane sulfonate, and water as the solvent.

[0248] The electroplating parameters are: electroplating temperature 25℃, current density 5A / dm³. 2 The pH value is less than 1.

[0249] Metal layers (copper layers) are electroplated on both sides of the alloy layer to form a composite foil current collector, which consists of the alloy layer and the alloy layers on both sides of the alloy layer. The average grain size of the copper layer is 150 nm.

[0250] (2) Preparation of negative electrode sheet.

[0251] The negative electrode active material (silicon-carbon composite and graphite in a mass ratio of 40:60), conductive agent carbon black, binder styrene-butadiene rubber, and thickener sodium hydroxymethyl cellulose are thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 93.5:1.8:3.5:1.2 to form a uniform negative electrode slurry. The negative electrode slurry is coated onto the negative electrode current collector, and after drying and other processes, the negative electrode sheet is obtained.

[0252] (3) Preparation of positive electrode sheet.

[0253] LiNi, the positive electrode active material 0.9 Co 0.05 Mn 0.05O2, conductive agent carbon black, and binder polyvinylidene fluoride are mixed evenly in N-methylpyrrolidone in a ratio of 96:2:2 to prepare a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil and dried, and then cold-pressed to prepare a positive electrode sheet.

[0254] (4) Separation membrane.

[0255] Polyethylene separator film.

[0256] (5) Electrolyte.

[0257] An organic solvent was prepared by mixing ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate in a volume ratio of 1:1:1. Lithium salt LiPF6 was dissolved in the organic solvent, and fluoroethylene carbonate (FEC) was added as an additive to prepare the electrolyte. The lithium salt concentration was 1 mol / L, and the mass percentage of FEC in the electrolyte was 5%.

[0258] (6) Battery assembly.

[0259] The positive electrode, separator, and negative electrode are wound in sequence to obtain an electrode assembly. The electrode assembly is placed in a housing, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0260] Examples 2-6, Comparative Examples 1-2

[0261] The preparation method of the negative electrode current collector is basically the same as in Example 1. The difference lies in adjusting the composition of the first electroplating solution and the electroplating parameters of the alloy layer electroplating treatment, as shown in Table 1.

[0262] The following are performance tests.

[0263] (1) Bending resistance of the negative electrode current collector

[0264] At 25℃, the current collector sample was folded 180° and then rolled back and forth at the fold with a 1.5kg roller. After unfolding, the sample was observed to see if cracking and light transmission occurred at the fold. The number of times the rolling caused cracking and light transmission at the fold was recorded. At least ten samples were tested, and the average value was taken as the bending resistance of the current collector. The results are shown in Table 2.

[0265] (2) Battery cycle performance

[0266] 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. n / Record the total number of cycles when C0 reaches 80%. 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 2.

[0267] It is understood that the test methods for the other performance parameters in Table 1 are the methods described in the corresponding section of this application.

[0268] Table 1

[0269]

[0270] Table 2

[0271]

[0272] In Table 2, the relative volume percentage of the γ solid solution phase represents the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase, and the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase. The relative volume percentage of the α solid solution phase represents the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase, and the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase. γ / α represents the ratio of the relative volume percentage of the γ solid solution phase to the relative volume percentage of the α solid solution phase. The percentage of the (111) crystal plane of the γ solid solution phase represents the percentage of the diffraction peak area of ​​the (111) crystal plane of the γ solid solution phase, based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase. The percentage of the (200) crystal plane of the γ solid solution phase represents the percentage of the diffraction peak area of ​​the (200) crystal plane of the γ solid solution phase, based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase.

[0273] As can be seen from Examples 1-6 and Comparative Examples 1-2, when the average grain size of the alloy layer is 15nm-60nm and the volume percentage of the γ solid solution phase is 50%-80%, the current collector can have high tensile strength and good toughness, thereby enabling the battery to have good cycle performance.

[0274] As can be seen from Examples 1 to 6, when the ratio of the relative volume percentage of the γ solid solution phase to the relative volume percentage of the α solid solution phase is 2 to 4, the tensile strength and toughness of the current collector can be further improved, and the cycle performance of the battery can be enhanced.

[0275] 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.

[0276] 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.

Claims

1. A current collector, characterized in that, The alloy layer includes nickel and iron elements, and has an average grain size of 15 nm to 60 nm. The alloy layer comprises a γ-solution phase and an α-solution phase. In the X-ray diffraction spectrum of the alloy layer, the γ solid solution phase includes (111) crystal plane and (200) crystal plane, and the α solid solution phase includes (110) crystal plane and (200) crystal plane; Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase is 50% to 80%.

2. The current collector as described in claim 1, characterized in that, Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase is 20% to 50%.

3. The current collector as described in claim 2, characterized in that, The ratio of the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase to the sum of the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase is greater than or equal to 1.2, and optionally 2 to 4.

4. The current collector as described in any one of claims 1 to 3, characterized in that, The nickel element accounts for 50% to 85% of the mass of the alloy layer.

5. The current collector as described in any one of claims 1 to 4, characterized in that, The iron element accounts for 15% to 50% of the mass of the alloy layer.

6. The current collector as described in any one of claims 1 to 5, characterized in that, The alloy layer satisfies one or more of the following characteristics: (1) Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the diffraction peak area of ​​the (111) crystal plane of the γ solid solution phase is 30%~50%; (2) Based on the sum of the diffraction peak areas of the (111) and (200) crystal planes of the γ solid solution phase and the diffraction peak areas of the (110) and (200) crystal planes of the α solid solution phase, the percentage of the diffraction peak area of ​​the (200) crystal plane of the γ solid solution phase is 20%~40%.

7. The current collector as described in any one of claims 1 to 6, characterized in that, The surface roughness Ra of the current collector is 20 nm to 120 nm.

8. The current collector according to any one of claims 1 to 7, characterized in that, The current collector satisfies one or more of the following characteristics: (1) The transverse tensile strength of the current collector is greater than or equal to 1200 MPa, and optionally 1500 MPa to 2200 MPa; (2) The transverse fracture elongation of the current collector is 2%~8%; (3) The thickness of the current collector is 2μm~10μm.

9. The current collector according to any one of claims 1 to 8, characterized in that, The current collector further includes a metal layer disposed on at least one side of the alloy layer; optionally, the metal layer includes one or more of Cu, Ni, Zn or Cr.

10. The current collector as described in claim 9, characterized in that, The average grain size of the metal layer is greater than the average grain size of the alloy layer; Optionally, the average grain size of the metal layer is 90nm~400nm, and optionally 100nm~300nm.

11. A method for preparing a current collector, characterized in that, Includes the following steps: An insoluble anode, a first electroplating solution, and a cathode are provided for electroplating to form an alloy layer on the surface of the cathode; after the electroplating process, the alloy layer is separated from the surface of the cathode. The first electroplating solution includes a nickel source, an iron source, a complexing agent, a first additive, and a second additive; the first additive includes one or more of saccharin, sodium saccharin, polyethylene glycol, polyethyleneimine, 1,4-butynediol, sodium naphthalene disulfonate, and formaldehyde; the second additive includes one or more of thiourea and its derivatives, and thiocyanate; in the first electroplating solution, the concentration of the iron source is 20 g / L to 80 g / L, and the concentration of the nickel source is 150 g / L to 250 g / L.

12. The method for preparing the current collector as described in claim 11, characterized in that, The first electroplating solution satisfies one or more of the following characteristics: (1) The concentration of the first additive is 3 g / L to 5 g / L; (2) The concentration of the second additive is 0.1 g / L to 0.5 g / L.

13. The method for preparing the current collector according to any one of claims 11-12, characterized in that, The first electroplating solution satisfies one or more of the following characteristics: (1) The complexing agent includes one or more of citric acid, sodium citrate, sodium gluconate and gluconic acid; (2) The first electroplating solution further includes an activator; optionally, the activator includes one or more of ammonium chloride and sodium chloride; optionally, the concentration of the activator is 10 g / L to 20 g / L; (3) The first electroplating solution further includes a wetting agent; optionally, the wetting agent includes at least one of sodium dodecyl sulfate and sodium dodecyl sulfonate; optionally, the concentration of the wetting agent in the electroplating solution is 0.1 g / L to 0.5 g / L; (4) The first electroplating solution further includes a conductive agent; optionally, the conductive agent includes at least one of sodium chloride, hydrochloric acid, and ammonium chloride; optionally, the concentration of the conductive agent in the electroplating solution is 10 g / L to 50 g / L. (5) The first electroplating solution further includes a stabilizer; optionally, the stabilizer includes at least one of boric acid, citric acid, and fluoroborate; optionally, the concentration of the stabilizer in the electroplating solution is 20 g / L to 80 g / L; (6) The first electroplating solution further includes an antioxidant; optionally, the antioxidant includes at least one 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. (7) The pH value of the first electroplating solution is 2~3.

14. The preparation method according to any one of claims 11 to 13, characterized in that, It meets one or more of the following characteristics: (1) The current density of the electroplating process is 6 A / dm. 2 ~8A / dm 2 ; (2) The rotational speed of the cathode is 0.5 m / min to 0.8 m / min; (3) The surface roughness Ra of the cathode is 100nm~200nm; (4) The flow rate of the first electroplating solution is 50L / min~80L / min.

15. 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 10 or any one of claims 11 to 14.

16. The secondary battery according to claim 15, characterized in that, The secondary battery includes a negative electrode sheet, the negative electrode sheet includes the current collector and a negative electrode film layer located on at least one surface of the current collector; the negative electrode film layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material; optionally, the mass percentage of the silicon-based material in the negative electrode active material is greater than or equal to 20%, more preferably 30% to 60%.

17. The secondary battery as described in claim 15, characterized in that, The secondary battery includes a wound electrode assembly, which includes a negative electrode sheet. The negative electrode sheet includes the current collector and a negative electrode film layer located on at least one surface of the current collector. The negative electrode film layer includes a negative electrode active material, which includes a silicon-based material. Optionally, the mass percentage of the silicon-based material in the negative electrode active material is greater than or equal to 20%, and more preferably 30% to 60%.

18. An electrical appliance, characterized in that, The secondary battery includes any one of claims 15 to 17.

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