Current collector, secondary battery, and electric device

Abstract

The invention provides a current collector, a secondary battery and an electric device. The current collector comprises two surface layers and a middle layer arranged between the two surface layers; the middle layer comprises a first element, and the first element comprises one or more of Fe, Zn, Pb and Mg; the surface layer comprises a second element, and the second element comprises one or more of Ni, Cr, Mo, Sn, Cu, Bi, W and Co; and the bonding strength between the surface layer and the middle layer is greater than 100N / m.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more particularly to a current collector, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, secondary 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 many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0003] Currently, the main cost of new energy vehicles comes from secondary batteries. How to further reduce the cost of secondary batteries without sacrificing their cycle performance, thereby enabling their wider application, is a pressing issue that needs to be addressed in this field. Summary of the Invention

[0004] This application is made in view of the above-mentioned issues, and its purpose is to provide a current collector that enables secondary batteries to have both low cost and long cycle life.

[0005] The first aspect of this application provides a current collector comprising two surface layers and an intermediate layer disposed between the two surface layers; the intermediate layer comprises a first element, the first element comprising one or more of Fe, Zn, Pb, and Mg; the surface layers comprise a second element, the second element comprising one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, and Co; and the bonding strength between the surface layers and the intermediate layer is greater than 100 N / m.

[0006] The first element in the intermediate layer is less expensive than commonly used metal foils (such as copper foil) in existing technologies, thus reducing the cost of rechargeable batteries. Furthermore, the metal composed of the first element has high strength, which helps improve the fracture strength of the current collector, reduces the probability of electrode wrinkling during cycling, and lowers the risk of electrode film pulverization and demolding or increased electrode polarization due to ion diffusion path extension, thereby reducing the risk of lithium plating during cycling. Additionally, the surface layer containing the second element, located on both sides of the intermediate layer surface, reduces the corrosion of the low-cost elements in the intermediate layer in the electrochemical environment, allowing the electrode to maintain good mechanical strength even in electrochemical conditions. While a corrosion-resistant surface layer on the intermediate layer surface improves the corrosion resistance of the current collector, cracks can easily form at weak points in the bond between the surface layer and the intermediate layer during cycling, creating localized galvanic cells and accelerating corrosion. Studies have shown that current collectors with a bonding strength between the surface layer and the intermediate layer within the aforementioned range can reduce the risk of cracking during cycling. The surface layer can provide long-term effective protection for the intermediate layer during cycling, delaying the occurrence of intermediate layer corrosion and comprehensively improving the cycle stability of the battery.

[0007] In any implementation, the intermediate layer includes at least one first element and at least one second element, wherein the mass percentage of the first element is greater than or equal to 50% based on the total mass of the elements in the intermediate layer.

[0008] The high-quality first element in the intermediate layer can reduce electrode manufacturing costs, resulting in a significant decrease in the cost of rechargeable batteries. Including a second element in the intermediate layer can further improve electrode strength and stability through alloying of at least two elements, thereby improving the cycle life of the rechargeable battery.

[0009] In any implementation, the mass percentage of the first element is 70% to 95% based on the total mass of the elements in the intermediate layer.

[0010] In any embodiment, the surface layer includes at least one second element and at least one first element, wherein the mass percentage of the second element is greater than or equal to 50% based on the total mass of the elements in the surface layer.

[0011] The high-quality proportion of the second element in the surface layer can balance the low cost, high strength and stability of the electrode, enabling the secondary battery to achieve both low cost and long cycle life.

[0012] In any implementation, the second element accounts for 70% to 95% of the total mass of the elements in the surface layer.

[0013] In any embodiment, based on the total thickness of the current collector, the thickness of the intermediate layer accounts for more than or equal to 50%, and the total thickness of the surface layer accounts for less than or equal to 50%.

[0014] Current collectors with a thickness ratio within the above range can reduce costs while maintaining the electrochemical stability of the electrode, thereby achieving both cost reduction and lifespan improvement for secondary batteries.

[0015] In any embodiment, based on the total thickness of the current collector, the thickness of the intermediate layer accounts for 70%-95%, and the total thickness of the surface layer accounts for 5%-30%.

[0016] Current collectors with thicknesses within the above range can balance low cost and high cycle life of secondary batteries.

[0017] In any embodiment, the bond strength between the surface layer and the intermediate layer is 150 N / m to 500 N / m.

[0018] For current collectors where the bonding strength between the surface layer and the intermediate layer is within the above-mentioned range, the surface layer can provide more effective protection for the intermediate layer, delay the occurrence of intermediate layer corrosion, and comprehensively improve the cycle stability of the battery.

[0019] In any embodiment, the ratio of the average grain size of the surface layer to the average grain size of the intermediate layer is greater than 1.8, and can be selected as 2.8 to 100, or more preferably 3 to 5.7.

[0020] The ratio of the average grain size of the surface layer to the average grain size of the intermediate layer is within the above range, indicating that the intermediate layer has fewer grain boundaries than the surface layer. This helps to reduce the proportion of grain boundaries in the surface layer, delays the probability of large-area corrosion of the intermediate layer caused by intergranular corrosion of the current collector, further improves the corrosion resistance of the low-cost current collector, and comprehensively improves the cycle life of the battery.

[0021] In any embodiment, the surface layer includes a first surface layer near the intermediate layer and a second surface layer disposed on the side of the first surface layer opposite to the intermediate layer, wherein the first surface layer and the second surface layer each independently include at least one second element.

[0022] The multi-layer design of the surface layer enables customized design of electrode performance, simultaneously improving properties such as tensile strength, elongation at break, and chemical stability.

[0023] In any embodiment, the thickness of the current collector is 2μm to 20μm, and can be selected as 4μm to 10μm.

[0024] In any implementation, based on the total mass of the elements in the current collector, the total mass ratio of the first element and the second element in the current collector is greater than or equal to 95%.

[0025] In any embodiment, the tensile breaking strength of the current collector is 400MPa-1600MPa, and / or the elongation at break of the current collector is 2%-10%.

[0026] In any embodiment, the tensile breaking strength of the current collector is 500MPa-1200MPa, and / or the elongation at break of the current collector is 5%-8%.

[0027] This current collector possesses both excellent tensile strength and good elongation at break, which is beneficial for improving the cycle life of secondary batteries.

[0028] In any embodiment, the intermediate layer is prepared by calendering or electroplating, and the surface layer is prepared by physical vapor deposition, chemical vapor deposition, or electroplating.

[0029] The preparation method of the intermediate layer can further reduce the manufacturing cost of the electrode, thereby achieving cost reduction of the secondary battery. The above-mentioned preparation method of the surface layer can improve the bonding strength between the surface layer and the intermediate layer, thus improving the cycle life of the secondary battery.

[0030] In any embodiment, the intermediate layer is surface-etched, and then the surface layer is deposited on the intermediate layer.

[0031] Depositing the surface layer after surface etching of the intermediate layer helps to improve the bonding strength between the intermediate layer and the surface layer, reduce the risk of current collector corrosion, and improve the cycle life of the secondary battery.

[0032] A second aspect of this application provides a secondary battery, which includes a negative electrode sheet, the negative electrode sheet including a current collector as described in the first aspect and a negative electrode film layer disposed on at least one side of the current collector.

[0033] In the prior art, the current collector in the negative electrode is mostly copper foil, and this component accounts for nearly 10% of the total cost of the secondary battery. The current collector in the embodiment of this application can significantly reduce the cost of the secondary battery and at the same time improve the cycle life of the secondary battery. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a current collector according to one embodiment of this application.

[0035] Figure 2 This is a schematic diagram of a current collector according to another embodiment of this application.

[0036] Figure 3 This is a schematic diagram of one embodiment of the secondary battery of this application;

[0037] Figure 4 This is an exploded view of one embodiment of the secondary battery of this application;

[0038] Figure 5 This is a schematic diagram of one embodiment of the battery module of this application;

[0039] Figure 6 This is a schematic diagram of one embodiment of the battery pack of this application;

[0040] Figure 7 yes Figure 6 An exploded view of an embodiment of the battery pack shown;

[0041] Figure 8 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Housing; 52 Electrode assembly; 53 Cover plate; 6 Current collector; 61 Intermediate layer; 62 Surface layer; 62-1 First surface layer; 62-2 Second surface layer. Detailed Implementation

[0044] The following describes in detail embodiments of the current collector, secondary battery, and power supply device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0045] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; 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 understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are 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 "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0046] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0047] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0048] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0049] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0050] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0051] With the widespread application of rechargeable batteries, the industry has been pursuing a common goal of using low-cost metals (such as Fe, Zn, Pb, and Mg) to replace commonly used metal foils (such as copper foil) as current collectors in order to reduce the cost of rechargeable batteries. However, these low-cost metals have poor corrosion resistance in electrochemical environments and their mechanical strength decreases during cycling. This makes the current collectors prone to wrinkling or even breakage during cycling, resulting in decreased battery cycle stability and making it difficult to meet market demands for rechargeable batteries.

[0052] Based on this, this application provides a current collector that can reduce the cost of secondary batteries while ensuring the cycle stability of the secondary batteries.

[0053] [Rechargeable Battery]

[0054] In one embodiment of this application, such as Figure 1 As shown, a current collector 6 is provided, which includes two surface layers 62 and an intermediate layer 61 disposed between the two surface layers 62. The intermediate layer 61 includes a first element, which includes one or more of Fe, Zn, Pb, and Mg. The surface layers 62 include a second element, which includes one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, and Co. The bonding strength between the surface layers and the intermediate layer is greater than 100 N / m.

[0055] The layered structure of the electrode can be obtained by any method known in the art. As an example, the electrode is cut along its thickness, and the elements in the longitudinal section are characterized using metallographic, scanning electron microscopy, and energy dispersive spectroscopy (EDS) instruments. The surface layer refers to the region extending from the surface of the current collector towards the thickness direction, with the intermediate layer adjacent to the surface layers on either side, situated between the surface layers. The elemental composition of each layer can be obtained by EDS analysis of the cross-section or surface of each layer of the current collector; its composition can be homogeneous or non-homogeneous, and the surface layer can be a single layer or include multiple layers. It should be noted that the surface layer and the intermediate layer can be identified by a clear compositional boundary in the cross-section of the current collector, but this does not necessarily mean that there is a clear layering in their cross-sectional morphology.

[0056] In some implementations, the intermediate layer comprises Fe.

[0057] Iron is a low-cost and abundant element that can significantly reduce the cost of electrode manufacturing, thus driving down the cost of rechargeable batteries. Furthermore, iron has a lower density than copper foil, which is commonly used in existing technologies, contributing to battery weight reduction and further improving energy density.

[0058] In some implementations, the intermediate layer includes at least two first elements.

[0059] In some embodiments, the surface layer includes one or more of Ni, Cr, Mo, W, and Cu.

[0060] Ni, Cr, Mo, and W not only improve the corrosion resistance of current collectors but also enable close packing of the crystal lattice, which is beneficial for increasing the strength of the current collector, suppressing the expansion and contraction of the current collector during the insertion and extraction of active ions, reducing the risk of wrinkling or even breakage of the electrode, and improving the cycle life and safety of the secondary battery. Copper not only improves the corrosion resistance of current collectors but also has good electrical conductivity, which can improve the current carrying capacity of the current collector and enhance the electrochemical performance of the secondary battery.

[0061] In some implementations, the surface layer includes at least two second elements.

[0062] In some embodiments, the surface layer comprises an alloy of Ni and W. In some embodiments, the surface layer comprises an alloy of Ni and Cr. In some embodiments, the surface layer comprises an alloy of Ni and Mo. In some embodiments, the surface layer comprises an alloy of Ni and Sn. In some embodiments, the surface layer comprises an alloy of Ni and Cu. In some embodiments, the surface layer comprises an alloy of Ni and Bi. In some embodiments, the surface layer comprises an alloy of Ni and Co.

[0063] The strength of the current collector can be further improved by alloying with at least two second elements, thereby improving the cycle life of the secondary battery.

[0064] The bond strength between the surface layer and the intermediate layer can be tested using a peel strength tester according to any known method. As an example, a wide adhesive tape (e.g., high-viscosity 3M tape) with a high bond strength and a width of 24 mm (W) is tightly adhered to the surface of the current collector. After rolling it back and forth three times with a 2 kg roller, one side of the tape is torn and placed in the upper clamp of a tensile testing machine, with the current collector clamped in the lower clamp. The tensile testing machine is started, and the tape is stretched upwards at a stretching rate of 1 mm / min. The average value of the peel force (F, unit: N) is taken as the surface layer peel force after the force value in the stretching curve no longer increases linearly and enters the fluctuation range, and the displacement length is greater than 25 mm. For samples with surface layer peeling as the failure mode, the bond strength can be calculated using the formula P = F / W, in N / m. For samples with tape peeling as the failure mode, it can be determined that the bond strength between the surface layer and the intermediate layer is greater than the tape peel strength.

[0065] In some embodiments, the bond strength between the surface layer and the intermediate layer can be selected as 100 N / m, 110 N / m, 120 N / m, 130 N / m, 140 N / m, 150 N / m, 200 N / m, 250 N / m, 300 N / m, 350 N / m, 400 N / m, 450 N / m, 500 N / m, 600 N / m, 700 N / m, 800 N / m, 900 N / m, or any value range between the two.

[0066] The first element in the intermediate layer is less expensive than commonly used metal foils (such as copper foil) in existing technologies, thus reducing the cost of rechargeable batteries. Furthermore, the metal composed of the first element has high strength, which helps improve the fracture strength of the current collector, reduces the probability of electrode wrinkling during cycling, and lowers the risk of electrode film pulverization and demolding or increased electrode polarization due to ion diffusion path extension, thereby reducing the risk of lithium plating during cycling. Additionally, the surface layer containing the second element, located on both sides of the intermediate layer surface, reduces the corrosion of the low-cost elements in the intermediate layer in the electrochemical environment, allowing the electrode to maintain good mechanical strength even in electrochemical conditions. While a corrosion-resistant surface layer on the intermediate layer surface improves the corrosion resistance of the current collector, cracks can easily form at weak points in the bond between the surface layer and the intermediate layer during cycling, creating localized galvanic cells and accelerating corrosion. Studies have shown that current collectors with a bonding strength between the surface layer and the intermediate layer within the aforementioned range can reduce the risk of cracking during cycling. The surface layer can provide long-term effective protection for the intermediate layer during cycling, delaying the occurrence of intermediate layer corrosion and comprehensively improving the cycle stability of the battery.

[0067] In some embodiments, the intermediate layer includes at least one first element and at least one second element, wherein the mass percentage of the first element is greater than or equal to 50% based on the total mass of the elements in the intermediate layer.

[0068] Based on the total mass of the elements in the intermediate layer, the mass percentage of the first element can be tested using any known method. As an example, elemental analysis is performed on multiple regions of the intermediate layer randomly selected using energy dispersive spectroscopy, with the selected regions at least 0.5 μm away from the surface layer. The mass percentage of the first element in each region is obtained, and the average of the mass percentages of the first element in at least 10 regions is taken as the mass percentage of the first element in the intermediate layer.

[0069] In some implementations, based on the total mass of the elements in the intermediate layer, the mass percentage of the first element can be selected as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or any value range between the two.

[0070] In some embodiments, the intermediate layer comprises an alloy of Fe and Ni. In some embodiments, the intermediate layer comprises an alloy of Fe and Mo. In some embodiments, the intermediate layer comprises an alloy of Fe and Cr. In some embodiments, the intermediate layer comprises an alloy of Fe and Sn. In some embodiments, the intermediate layer comprises an alloy of Fe and Cu. In some embodiments, the intermediate layer comprises an alloy of Fe and Bi. In some embodiments, the intermediate layer comprises an alloy of Fe and W. In some embodiments, the intermediate layer comprises an alloy of Fe and Co.

[0071] The high-quality first element in the intermediate layer can reduce electrode manufacturing costs, resulting in a significant decrease in the cost of rechargeable batteries. Including a second element in the intermediate layer can further improve electrode strength and stability through alloying of at least two elements, thereby improving the cycle life of the rechargeable battery.

[0072] In some implementations, the mass percentage of the first element is 70% to 95% based on the total mass of the elements in the intermediate layer.

[0073] In some embodiments, the surface layer includes at least one second element and at least one first element, wherein the second element accounts for more than or equal to 50% of the total mass of the elements in the surface layer.

[0074] Based on the total mass of the elements in the surface layer, the mass percentage of the second element can be tested using any known method. Specifically, the method for testing the mass percentage of the first element in the intermediate layer described above can be used for testing.

[0075] In some implementations, based on the total mass of the elements in the surface layer, the mass percentage of the second element can be selected as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or any range between the two.

[0076] The high-quality proportion of the second element in the surface layer can balance the low cost, high strength and stability of the electrode, enabling the secondary battery to achieve both low cost and long cycle life.

[0077] In some implementations, the second element accounts for 70% to 95% of the total mass of the elements in the surface layer.

[0078] In some implementations, based on the total thickness of the current collector, the thickness of the intermediate layer accounts for more than or equal to 50%, and the total thickness of the surface layer accounts for less than or equal to 50%.

[0079] Based on the total thickness of the current collector, the thickness percentage of the intermediate layer can be tested using any method known in the art. As an example, the prepared current collector is quenched in liquid nitrogen, and the cross-sectional morphology of the intermediate layer is observed using a scanning electron microscope to measure its thickness. It should be understood that the thickness of one side of the surface layer can be tested using the same or similar methods; the sum of the thicknesses of both surface layers divided by the total thickness of the current collector is taken as the total thickness percentage of the surface layer.

[0080] In some embodiments, based on the total thickness of the current collector, the thickness percentage of the intermediate layer can be selected as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or any value range between the two.

[0081] In some embodiments, based on the total thickness of the current collector, the percentage of the total thickness of the surface layer can be selected as 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any value range between the two.

[0082] Current collectors with a thickness ratio within the above range can reduce costs while maintaining the electrochemical stability of the electrode, thereby achieving both cost reduction and lifespan improvement for secondary batteries.

[0083] In some embodiments, based on the total thickness of the current collector, the thickness of the intermediate layer accounts for 70%-95%, and the total thickness of the surface layer accounts for 5%-30%.

[0084] Current collectors with thicknesses within the above range can balance low cost and high cycle life of secondary batteries.

[0085] In some embodiments, the bond strength between the surface layer and the intermediate layer is 150 N / m to 500 N / m.

[0086] For current collectors where the bonding strength between the surface layer and the intermediate layer is within the above-mentioned range, the surface layer can provide more effective protection for the intermediate layer, delay the occurrence of intermediate layer corrosion, and comprehensively improve the cycle stability of the battery.

[0087] In some embodiments, the ratio of the average grain size of the surface layer to the average grain size of the intermediate layer is greater than 1.8, and can be selected as 2.8 to 100, or more preferably 3 to 5.7.

[0088] The average grain size of the surface layer or intermediate layer can be characterized by X-ray diffraction (XRD) tests on current collectors in different regions. The cross-section of the current collector is observed to identify the thickness of the surface layer and intermediate layer in the current collector, and samples to be tested are obtained in different thickness ranges. As an example, the X-ray diffraction pattern of the current collector sample with CuKα rays as the radiation source is obtained by an X-ray diffractometer, and the average grain size is calculated by the Scherrer formula D=Kλ / (βcosθ), where D is the average grain size, K is a constant, λ is the X-ray wavelength of 0.154nm, β is the half width at half maximum (FWHM) of the diffraction peak, and θ is the diffraction angle. To enhance the comparability of data, the same diffraction angle of the same crystal plane is selected as the basis for judging the grain size for both the surface layer and the intermediate layer. For example, the diffraction angle of the (111) crystal plane is selected for grain size calculation.

[0089] In some embodiments, the ratio of the average grain size of the surface layer to the average grain size of the intermediate layer can be selected as 1.96, 2, 2.8, 3, 4, 4.7, 5, 5.7, 10, 20, 30, 40, 50, 100 or any value range between the two.

[0090] The ratio of the average grain size of the surface layer to the average grain size of the intermediate layer is within the above range, indicating that the intermediate layer has fewer grain boundaries than the surface layer. This helps to reduce the proportion of grain boundaries in the surface layer, delays the probability of large-area corrosion of the intermediate layer caused by intergranular corrosion of the current collector, further improves the corrosion resistance of the low-cost current collector, and comprehensively improves the cycle life of the battery.

[0091] In some implementations, such as Figure 2 As shown, the surface layer 62 includes a first surface layer 62-1 near the intermediate layer 61 and a second surface layer 62-2 disposed on the side of the first surface layer 62-1 away from the intermediate layer 61. The first surface layer 62-1 and the second surface layer 62-2 each independently include at least one second element.

[0092] It is understandable that the composition of the second element in the first surface layer and the second element in the second surface layer can be completely the same, partially the same, or completely different.

[0093] In some implementations, the second element in the first surface layer has a different composition than the second element in the second surface layer.

[0094] The multi-layer design of the surface layer enables customized design of electrode performance, simultaneously improving properties such as tensile strength, elongation at break, and chemical stability.

[0095] In some implementations, the first surface layer comprises Ni and the second surface layer comprises Cu.

[0096] This electrode has both good strength and elongation, which can comprehensively improve the cycle life of secondary batteries.

[0097] In some embodiments, the thickness of the current collector is 2 μm to 20 μm, and can be selected as 4 μm to 10 μm.

[0098] In some embodiments, the thickness of the current collector can be selected as 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or any value range between the two.

[0099] In some implementations, based on the total mass of the elements in the current collector, the total mass ratio of the first element and the second element in the current collector is greater than or equal to 95%.

[0100] Based on the total mass of the elements in the current collector, the total mass ratio of the first element to the second element in the current collector can be determined by any method known in the art. As an example, the elemental composition and content of the current collector are tested using an inductively coupled plasma optical plasma (ICP) spectrometer.

[0101] In some embodiments, based on the total mass of the current collector, the total mass ratio of the first element and the second element in the current collector can be selected as 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 100%, or any value range between the two.

[0102] In some embodiments, the tensile breaking strength of the current collector is 400MPa-1600MPa, and / or the elongation at break of the current collector is 2%-10%.

[0103] In some embodiments, the tensile breaking strength of the current collector can be selected as 400MPa, 500MPa, 600MPa, 700MPa, 800MPa, 900MPa, 1000MPa, 1100MPa, 1200MPa, 1300MPa, 1400MPa, 1500MPa, 1600MPa or any value range between the two.

[0104] In some embodiments, the elongation at break of the current collector can be selected as 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value range between the two.

[0105] The tensile strength and elongation at break of the current collector can be tested using methods known in the art. As an example, the current collector is cut into specimens with a length of 150 mm and a width of 15 mm. A tensile testing machine (e.g., an Instron 3343 tensile testing machine) is used to perform a tensile test at a tensile speed of 5 mm / min with a gauge length of 50 mm. The tensile strength at break of the specimen is calculated by dividing the maximum tensile force in the tensile curve by the area. The elongation at break is calculated as the ratio of the elongation at break to the length before tensile testing. Each specimen is tested in parallel 10 times, and the average value is calculated as the tensile strength at break and the tensile elongation at break of the specimen.

[0106] In some embodiments, the tensile breaking strength of the current collector is 500MPa-1200MPa, and / or the elongation at break of the current collector is 5%-8%.

[0107] This current collector possesses both excellent tensile strength and good elongation at break, which is beneficial for improving the cycle life of secondary batteries.

[0108] In some embodiments, the intermediate layer is prepared by calendering or electroplating, and the surface layer is prepared by physical vapor deposition, chemical vapor deposition, or electroplating.

[0109] The preparation method of the intermediate layer can further reduce the manufacturing cost of the electrode, thereby achieving cost reduction of the secondary battery. The above-mentioned preparation method of the surface layer can improve the bonding strength between the surface layer and the intermediate layer, thus improving the cycle life of the secondary battery.

[0110] In some embodiments, the intermediate layer is surface-etched before the surface layer is deposited on the intermediate layer.

[0111] Depositing the surface layer after surface etching of the intermediate layer helps to improve the bonding strength between the intermediate layer and the surface layer, reduce the risk of current collector corrosion, and improve the cycle life of the secondary battery.

[0112] A second aspect of this application provides a secondary battery, the secondary battery including a negative electrode sheet, the negative electrode sheet including a current collector as described in the first aspect and a negative electrode film layer disposed on at least one side of the current collector.

[0113] In the prior art, the current collector in the negative electrode is mostly copper foil, and this component accounts for nearly 10% of the total cost of the secondary battery. The current collector in the embodiment of this application can significantly reduce the cost of the secondary battery and at the same time improve the cycle life of the secondary battery.

[0114] In some embodiments, the film layer includes a negative electrode active material, which includes, but is not limited to, one or more of conventional natural graphite, artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate.

[0115] In some embodiments, the negative electrode active material includes a silicon-based material, which includes one or more of nano-silicon, silicon-carbon, silicon-oxygen, silicon-nitrogen, and silicon alloys.

[0116] Silicon-based materials are advantageous for improving the energy density of secondary batteries. However, silicon-based materials exhibit a large expansion rate during battery cycling, which can easily lead to cracking or even breakage of the current collector. The secondary battery of the present application is particularly suitable for battery systems incorporating silicon-based materials, enabling secondary batteries to achieve both good cycle life and safety performance at high energy density.

[0117] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0118] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0119] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0120] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0121] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0122] [Positive electrode plate]

[0123] In some implementations, the secondary battery includes a positive electrode.

[0124] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The positive electrode film layer includes the positive electrode active material of the first aspect of this application, and the current collector is the battery aluminum foil of this application. When applied to secondary batteries, the battery aluminum foil of this application can effectively improve the brittleness of the battery electrode and enhance the wrinkle resistance of the aluminum foil.

[0125] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, the battery aluminum foil of this application 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 may be formed by forming the battery aluminum foil of this application on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0126] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0127] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0128] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0129] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g. N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a positive current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0130] [Electrolytes]

[0131] In some implementations, the secondary battery includes an electrolyte.

[0132] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0133] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0134] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0135] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, 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.

[0136] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0137] [Isolation membrane]

[0138] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0139] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0140] A third aspect of this application provides an electrical device that includes a secondary battery in any embodiment.

[0141] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0142] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0143] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and the electrolyte.

[0144] 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. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0145] 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 3 This is an example of a square-structured secondary battery 5.

[0146] In some implementations, refer to Figure 4The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0147] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0148] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0149] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0150] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0151] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 6 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0152] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0153] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0154] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0155] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0156] Example

[0157] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0158] Example 1

[0159] (1) Preparation of current collector

[0160] Preparation of the intermediate layer:

[0161] Using a stainless steel plate as the cathode and a soluble iron plate as the anode, the plating solution consisted of 600 g / L ferric chloride, 300 g / L calcium chloride, and 0.5 g / L hydrochloric acid, with a current density of 10 A / dm³. 2 The pH was adjusted to 1.2-1.5, the electroplating temperature was 90℃, and iron foil was obtained by electroplating. After the iron foil was prepared, it was activated in a 5% dilute sulfuric acid environment to remove the oxide layer. The activation time was 30s and the thickness was 4μm.

[0162] Preparation of surface layer:

[0163] Using the intermediate layer prepared above as the cathode and a titanium-iridium alloy plate as the anode, the plating solution formula is: copper sulfate 200 g / L, sulfuric acid 50 g / L, polyethylene glycol (PEG) 0.8 g / L, sodium polydisulfide dipropane sulfonate (SPS) 5 mg / L, and the current density is 10 A / dm³. 2 The electroplating temperature is room temperature 25±5℃; copper layers are plated on both sides of the intermediate layer; the thickness of the Cu layer on each side is 0.5μm.

[0164] (2) Preparation of positive electrode sheet

[0165] A positive electrode slurry was prepared by uniformly mixing the positive electrode active material NCM811, conductive agent carbon black, and binder polyvinylidene fluoride (PVDF) in an N-methylpyrrolidone (NMP) solution at a mass ratio of 96:2:2. This slurry was then coated onto the surface of aluminum foil using an extrusion coating machine and dried to obtain the positive electrode film. The coated electrode was then cold-pressed using a cold press to obtain the final positive electrode sheet. The areal density of a single-sided film layer of the positive electrode sheet was 400 mg / 1540.25 mm². 2 The compaction density of the positive electrode sheet is 3.4 g / cm³. 3 .

[0166] (3) Preparation of negative electrode sheet

[0167] The negative electrode active material (a mixture of 30% silicon-carbon composite material and 70% graphite by mass), conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) were 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 was then coated onto a prepared current collector, and after drying and other processes, the negative electrode was obtained. The areal density of a single-sided film layer of the negative electrode sheet was 93.7 mg / 1540.25 mm². 2 The compaction density of the negative electrode sheet is 1.3 g / cm³. 3 .

[0168] (4) Separating membrane

[0169] Polyethylene diaphragm is used as the separation membrane.

[0170] (5) Electrolyte

[0171] Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. The fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0172] (6) Battery assembly

[0173] The positive electrode, separator, and negative electrode are wound in sequence to obtain an electrode assembly. The electrode assembly is placed in a packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion secondary battery is obtained.

[0174] Example 2

[0175] Example 2 is basically the same as Example 1, except that the surface layer is prepared using the following method:

[0176] Using the foil prepared above as the cathode and a titanium-iridium alloy plate as the anode, the plating solution formula is: nickel sulfate 200 g / L, sodium chloride 5 g / L, boric acid 30 g / L, sodium dodecyl sulfonate 0.1 g / L, and the current density is 1–1.5 A / dm³. 2 The pH was adjusted to 4–4.5, and the electroplating temperature was 45°C. Nickel layers were plated on both sides of the foil, with a surface layer thickness of 1 μm on each side.

[0177] Example 3

[0178] Example 3 is basically the same as Example 2, except that the surface layer is prepared using the following method:

[0179] Using the foil prepared above as the cathode and a titanium-iridium alloy plate as the anode, the plating solution formula is: nickel sulfate 200 g / L, nickel chloride 40 g / L, ferrous sulfate 20 g / L, boric acid 45 g / L, saccharin 3 g / L, sodium citrate 75 g / L, and the current density is 4 A / dm³. 2 Adjust the pH to 3.5–4 and the electroplating temperature to 55°C; plate nickel-iron alloy layers on both sides of the foil; the surface layer thickness on each side is 0.5 μm.

[0180] Example 4

[0181] Example 4 is basically the same as Example 2, except that the surface layer is prepared using the following method:

[0182] Using the foil prepared above as the cathode and the titanium-iridium alloy plate as the anode, the plating solution formula is: nickel sulfate 200 g / L, copper sulfate 50 g / L, boric acid 45 g / L, saccharin 3 g / L, sodium citrate 75 g / L, and the current density is 4 A / dm³. 2 Adjust the pH to 3.5-4 and the electroplating temperature to 40℃; plate nickel-copper alloy layers on both sides of the foil; the surface layer thickness on each side is 0.5μm.

[0183] Example 5

[0184] Example 5 is basically the same as Example 2, except that the surface layer is prepared using the following method:

[0185] Using the foil prepared above as the cathode and the titanium-iridium alloy plate as the anode, the plating solution formula is: nickel sulfate 60 g / L, sodium tungstate 150 g / L, citric acid 130 g / L, and the current density is 20 A / dm³. 2 The pH was adjusted to around 5 with ammonia, and the electroplating temperature was 35℃. Nickel-tungsten alloy layers were plated on both sides of the foil. The surface layer thickness on each side was 0.5μm.

[0186] Example 6

[0187] Example 6 is basically the same as Example 2, except that the intermediate layer is prepared using the following method:

[0188] Using a stainless steel plate as the cathode and a soluble iron plate as the anode, the plating solution formula is 70 g / L ferrous sulfate, 94 g / L sodium molybdate, and 230 g / L sodium citrate, with a current density of 0.5–1 A / dm³. 2 The pH was adjusted to 4-5, and the electroplating temperature was 30℃ to obtain an iron-molybdenum alloy foil with a thickness of 5μm.

[0189] Example 7

[0190] Example 7 is basically the same as Example 2, except for the preparation method of the intermediate layer. Specifically, the intermediate layer is prepared as follows:

[0191] Using a stainless steel plate as the cathode and a soluble iron plate as the anode, the plating solution formula was: nickel sulfate 0.3 mol / L, nickel chloride 0.05 mol / L, ferrous sulfate 0.15 mol / L, boric acid 0.5 mol / L, saccharin 2 g / L. The current was 5 A / dm², the rotation speed was 500 rpm / min, the pH was adjusted to 2.5-3, and the electroplating temperature was 55℃. Electroplating was carried out to obtain an iron-nickel alloy foil with a thickness of 5 μm.

[0192] Example 8

[0193] Example 8 is basically the same as Example 2, except that: the electroplating time of Fe foil is extended and the electroplating time of the two sides is reduced, so that the thickness of the middle layer is 5.8 μm, accounting for 97% of the thickness of the current collector; the thickness of the surface layer is 0.1 μm on both sides, accounting for 3% of the thickness of the current collector.

[0194] Example 9

[0195] Example 9 is basically the same as Example 3, except that the preparation method of the surface layer is adjusted.

[0196] Using the foil prepared above as the cathode and a titanium-iridium alloy plate as the anode, the plating solution formula is: nickel sulfate 200 g / L, nickel chloride 40 g / L, ferrous sulfate 20 g / L, boric acid 45 g / L, saccharin 3 g / L, sodium citrate 75 g / L, and the current density is 4 A / dm³. 2 The pH was adjusted to 3.5-4, and the electroplating temperature was 55°C. A first surface layer of nickel-iron alloy was plated on both sides of the foil. The thickness of the first surface layer was 0.5 μm. A copper layer was plated on both sides of the nickel-iron alloy layer according to the method of Example 1. The thickness of the copper layer on each side was 1 μm.

[0197] Example 10

[0198] The preparation method of the secondary battery in Example 10 is basically the same as that in Example 2, except that the activation time of the iron foil is adjusted to 10 seconds, thereby adjusting the interlayer bonding strength between the surface layer and the intermediate layer.

[0199] Example 11

[0200] The secondary battery preparation method in Example 11 is basically the same as that in Example 1, except that the current density during surface layer preparation is adjusted to 1 A / dm³. 2 This adjusts the ratio of the average grain size between the surface layer and the intermediate layer.

[0201] Comparative Example 1

[0202] The secondary battery preparation method of Comparative Example 1 is basically the same as that of Example 1, using commercially available copper foil as the negative electrode current collector.

[0203] Comparative Example 2

[0204] The preparation method of the secondary battery in Comparative Example 2 is basically the same as that in Example 1, using commercially available iron foil as the negative electrode current collector.

[0205] Performance testing

[0206] (1) Corrosion resistance test of current collector

[0207] The current collector was punched into a 14mm diameter disc to serve as the cathode, and a lithium sheet was used as the anode to assemble a coin cell. The cell was charged at a constant voltage of 4.5V for 7 days, and the voltage drop time was recorded after the voltage reached 4.5V.

[0208] (2) Battery cycle capacity retention rate

[0209] At 25℃, the battery is charged to 4.25V at a rate of 0.5C, and then discharged to 2.5V at a rate of 0.5C. This constitutes one cycle. The discharge capacity of the first cycle is recorded as C0, and the discharge capacity after 1000 cycles is recorded as C1000. The ratio of C1000 to C0 is used as the cycle capacity retention rate of the battery.

[0210] (3) Estimated Costs

[0211] With the cost of the high-performance copper foil in Comparative Example 1 as 100%, the cost of the current collector in the example is estimated.

[0212] Table 1

[0213]

[0214] Table 2

[0215]

[0216] Table 3

[0217]

[0218] Table 4

[0219]

[0220] Table 5

[0221]

[0222] As can be seen from the comparison between the embodiments and the comparative examples, the current collector includes a surface layer and an intermediate layer disposed between the surface layers. The intermediate layer includes a first element, which includes one or more of Fe, Zn, Pb, Mg, and Al. The surface layer includes a second element, which includes one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, and Co. This can improve the strength of the secondary battery and enhance its cycle life while reducing the cost of the secondary battery.

[0223] As can be seen from Table 2, the current collector provided in this application embodiment has better pressure resistance and durability compared to the pure iron current collector, indicating better corrosion resistance in an electrochemical environment.

[0224] As shown in Table 3, the surface layer includes a first surface layer close to the intermediate layer and a second surface layer disposed on the side of the first surface layer away from the intermediate layer. The first surface layer includes nickel and the second surface layer includes copper. This can improve the elongation at break of the current collector while enhancing the current collection, thereby comprehensively improving the cycle life of the secondary battery.

[0225] The bond strength between the surface layer and the intermediate layer is greater than 100 N / m. As shown in Table 4, a bond strength of ≥150 N / m between the surface layer and the intermediate layer is beneficial to improving the bonding performance between the intermediate layer and the surface layer, delaying the corrosion time of the intermediate layer, and further improving the corrosion resistance of the low-cost current collector.

[0226] As shown in Table 5, the ratio of the average grain size of the surface layer to the average grain size of the intermediate layer is greater than or equal to 2.8, which helps to reduce the proportion of grain boundaries in the surface layer, delays the probability of large-area corrosion of the intermediate layer caused by intergranular corrosion of the current collector, further improves the corrosion resistance of the low-cost current collector, and comprehensively improves the cycle life of the battery.

[0227] It should be noted that this application is not limited to the described embodiments. The described embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A current collector, characterized in that, The current collector includes two surface layers and an intermediate layer disposed between the two surface layers; the intermediate layer includes a first element, which includes one or more of Fe, Zn, Pb, and Mg; the surface layer includes a second element, which includes one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, and Co; the bonding strength between the surface layer and the intermediate layer is greater than 100 N / m.

2. The current collector according to claim 1, characterized in that, The intermediate layer includes at least one first element and at least one second element, and the mass percentage of the first element is greater than or equal to 50% based on the total mass of the elements in the intermediate layer.

3. The current collector according to claim 2, characterized in that, Based on the total mass of the elements in the intermediate layer, the mass percentage of the first element is 70% to 95%.

4. The current collector according to any one of claims 1 to 3, characterized in that, The surface layer includes at least one second element and at least one first element, and the second element accounts for more than or equal to 50% of the total mass of the elements in the surface layer.

5. The current collector according to claim 4, characterized in that, Based on the total mass of the elements in the surface layer, the mass percentage of the second element is 70% to 95%.

6. The current collector according to any one of claims 1 to 5, characterized in that, Based on the total thickness of the current collector, the thickness of the intermediate layer accounts for more than or equal to 50%, and the total thickness of the surface layer accounts for less than or equal to 50%.

7. The current collector according to any one of claims 1 to 6, characterized in that, Based on the total thickness of the current collector, the thickness of the intermediate layer accounts for 70%-95%, and the total thickness of the surface layer accounts for 5%-30%.

8. The current collector according to any one of claims 1 to 7, characterized in that, The bonding strength between the surface layer and the intermediate layer is 150 N / m to 500 N / m.

9. The current collector according to any one of claims 1 to 8, characterized in that, The ratio of the average grain size of the surface layer to the average grain size of the intermediate layer is greater than 1.8, and can be selected as 2.8 to 100, or more preferably 3 to 5.

7.

10. The current collector according to any one of claims 1 to 9, characterized in that, The surface layer includes a first surface layer near the intermediate layer and a second surface layer disposed on the side of the first surface layer opposite to the intermediate layer, wherein the first surface layer and the second surface layer each independently include at least one second element.

11. The current collector according to any one of claims 1 to 10, characterized in that, The thickness of the current collector is 2μm to 20μm, and can be selected as 4μm to 10μm.

12. The current collector according to any one of claims 1 to 11, characterized in that, Based on the total mass of the elements in the current collector, the total mass ratio of the first element and the second element in the current collector is greater than or equal to 95%.

13. The current collector according to any one of claims 1 to 12, characterized in that, The tensile breaking strength of the current collector is 400MPa-1600MPa, and / or the elongation at break of the current collector is 2%-10%.

14. The current collector according to any one of claims 1 to 13, characterized in that, The tensile breaking strength of the current collector is 500MPa-1200MPa, and / or the elongation at break of the current collector is 5%-8%.

15. The current collector according to any one of claims 1 to 14, characterized in that, The intermediate layer is prepared by calendering or electroplating, and the surface layer is prepared by physical vapor deposition, chemical vapor deposition, or electroplating.

16. The current collector according to any one of claims 1 to 15, characterized in that, After the intermediate layer is etched, the surface layer is deposited on the intermediate layer.

17. A secondary battery, characterized in that, The secondary battery includes a negative electrode sheet, which includes a current collector as described in any one of claims 1 to 16 and a negative electrode film layer disposed on at least one side of the current collector.

18. The secondary battery according to claim 17, characterized in that, The negative electrode film layer includes a negative electrode active material, which includes a silicon-based material, and the silicon-based material includes one or more of nano-silicon, silicon-carbon material, silicon-oxygen material, silicon-nitrogen material, and silicon alloy.

19. An electrical device comprising the secondary battery as described in claim 17 or 18.

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