Current collector, secondary battery, and electrical apparatus

Abstract

The present application provides a current collector, a secondary battery, and an electrical apparatus. The current collector comprises two surface layers and an intermediate layer provided between the two surface layers. The intermediate layer comprises a first element. The first element comprises one or more of Fe, Zn, Pb, and Mg. Each surface layer comprises a second element. The second element comprises one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, and Co. The bonding strength between each surface layer and the intermediate layer is greater than 100 N / m.

Description

Current collector, secondary battery, and electric device

[0001] Cross-reference to related applications

[0002] This application is based on the Chinese Patent Application No. 2024111244037 entitled "Current collector, secondary battery, and electric device" filed on August 15, 2024, which is incorporated by reference in its entirety. TECHNICAL FIELD

[0003] The present application relates to the technical field of secondary batteries, and in particular to a current collector, a secondary battery, and an electric device. BACKGROUND

[0004] In recent years, secondary batteries are widely used in energy storage power systems such as hydroelectric, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc.

[0005] At present, the main cost of new energy vehicles comes from secondary batteries. How to further reduce the cost of secondary batteries without sacrificing the cycle performance of secondary batteries so that their application can be further promoted is a problem that needs to be solved in the field. SUMMARY

[0006] The present application is made in view of the above-mentioned problem, and aims to provide a current collector that enables a secondary battery to have both low cost and long cycle life.

[0007] A first aspect of the present application provides a current collector, the 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 layer comprises a second element, the second element comprising 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.

[0008] The first element in the middle layer is less expensive than the metal foil (e.g., copper foil) commonly used in the prior art, which can reduce the cost of the secondary battery. Moreover, the metal composed of the first element has high strength, which is conducive to improving the breaking strength of the current collector, reducing the probability of wrinkling of the electrode sheet during the cycle process, reducing the risk of electrode sheet film layer powdering demolding or electrode polarization increase due to ion diffusion path increase, and reducing the risk of lithium precipitation of the electrode sheet during the cycle process. In addition, the surface layer containing the second element is arranged on both sides of the surface of the middle layer, which can reduce the corrosion degree of the low-cost element in the middle layer in the electrochemical environment, so that the electrode sheet still maintains good mechanical strength in the electrochemical environment. Although the corrosion-resistant surface layer arranged on the surface of the middle layer is conducive to improving the corrosion resistance of the current collector, the weak bond between the surface layer and the middle layer is prone to crack during the cycle process, which produces local primary cells and accelerates corrosion. Studies have shown that the current collector with a bonding strength between the surface layer and the middle layer within the above range can reduce the risk of cracking of the surface layer and the middle layer during the cycle process, and the surface layer can effectively protect the middle layer during the cycle process, delay the occurrence of middle layer corrosion, and improve the cycle stability of the battery.

[0009] In any embodiment, the middle layer comprises 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 middle layer.

[0010] The high mass percentage of the first element in the middle layer can reduce the cost of the electrode sheet and significantly reduce the cost of the secondary battery. The presence of the second element in the middle layer can further improve the strength and stability of the electrode sheet through alloying of at least two elements, thereby improving the cycle life of the secondary battery.

[0011] In any embodiment, the mass percentage of the first element is 70% to 95% based on the total mass of the elements in the middle layer.

[0012] In any embodiment, the surface layer comprises at least one second element and at least one first element, and 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.

[0013] The high mass percentage of the second element in the surface layer can balance the low cost, high strength, and stability of the electrode sheet, so that the secondary battery can simultaneously achieve low cost and long cycle life.

[0014] In any embodiment, the mass percentage of the second element is 70% to 95% based on the total mass of the elements in the surface layer.

[0015] In any embodiment, the thickness percentage of the middle layer is greater than or equal to 50% based on the total thickness of the current collector, and the total thickness percentage of the surface layer is less than or equal to 50%.

[0016] The current collector with the thickness ratio within the above range can reduce the cost while considering the electrochemical stability of the pole piece, and can reduce the cost and improve the service life of the secondary battery.

[0017] In any embodiment, the thickness ratio of the intermediate layer is 70%-95% and the total thickness ratio of the surface layer is 5%-30% based on the total thickness of the current collector.

[0018] The current collector with the thickness within the above range can consider the low cost and high cycle life of the secondary battery.

[0019] In any embodiment, the bonding strength between the surface layer and the intermediate layer is 150 N / m-500 N / m.

[0020] The current collector with the bonding strength between the surface layer and the intermediate layer within the above range can effectively protect the intermediate layer by the surface layer, delay the occurrence of corrosion of the intermediate layer, and improve the cycle stability of the battery.

[0021] 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 2.8-100, and further can be 3-5.7.

[0022] The ratio of the average grain size of the surface layer to the average grain size of the intermediate layer within the above range indicates that the intermediate layer has fewer grain boundaries than the surface layer, which is beneficial to reduce the grain boundary ratio of the surface layer, delay the probability of large-area corrosion of the intermediate layer caused by intergranular corrosion of the current collector, further improve the corrosion resistance of the low-cost current collector, and improve the cycle life of the battery.

[0023] In any embodiment, 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, and the first surface layer and the second surface layer each independently include at least one second element.

[0024] The multi-layer design of the surface layer can realize the customized design of the pole piece performance, and consider the simultaneous improvement of the performance of the pole piece including tensile strength, elongation at break, chemical stability, etc.

[0025] In any embodiment, the thickness of the current collector is 2 μm-20 μm, and can be 4 μm-10 μm.

[0026] In any embodiment, the total mass ratio of the first element and the second element in the current collector is greater than or equal to 95% based on the total mass of the elements in the current collector.

[0027] In any embodiment, the tensile fracture strength of the current collector is 400 MPa-1600 MPa, and / or the elongation at break of the current collector is 2%-10%.

[0028] In any embodiment, the tensile fracture strength of the current collector is 500-1200 MPa, and / or the elongation at break of the current collector is 5-8%.

[0029] The current collector has excellent tensile fracture strength and good elongation at break, which is conducive to improving the cycle life of the secondary battery.

[0030] 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.

[0031] The preparation method of the intermediate layer can further reduce the manufacturing cost of the pole piece, realizing the low cost of the secondary battery. The above preparation method of the surface layer can improve the bonding strength between the surface layer and the intermediate layer, and improve the cycle life of the secondary battery.

[0032] In any embodiment, the intermediate layer is subjected to surface corrosion, and then the surface layer is deposited on the intermediate layer.

[0033] The surface corrosion of the intermediate layer and then the deposition of the surface layer are conducive to improving the bonding strength between the intermediate layer and the surface layer, reducing the corrosion risk of the current collector, and improving the cycle life of the secondary battery.

[0034] The second aspect of the application provides a secondary battery, which comprises a negative pole piece, and the negative pole piece comprises the current collector of the first aspect and a negative film layer arranged on at least one side of the current collector.

[0035] In the prior art, the current collector in the negative pole piece 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 the application can significantly reduce the cost of the secondary battery, and at the same time improve the cycle life of the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0036] FIG. 1 is a schematic diagram of a current collector according to an embodiment of the application;

[0037] FIG. 2 is a schematic diagram of a current collector according to another embodiment of the application;

[0038] FIG. 3 is a schematic diagram of a secondary battery according to an embodiment of the application;

[0039] FIG. 4 is an exploded schematic diagram of a secondary battery according to an embodiment of the application;

[0040] FIG. 5 is a schematic diagram of a battery module according to an embodiment of the application;

[0041] FIG. 6 is a schematic diagram of a battery pack according to an embodiment of the application;

[0042] FIG. 7 is an exploded schematic view of the embodiment of the battery pack shown in FIG. 6;

[0043] FIG. 8 is a schematic view of an embodiment of an electrical device including the secondary battery of the present application as a power source.

[0044] BRIEF DESCRIPTION OF DRAWINGS 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 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 DESCRIPTION

[0045] Hereinafter, embodiments of the current collector, secondary battery, and electrical device of the present application will be described in detail. However, there will be cases where unnecessary detailed descriptions are omitted. For example, there will be cases where detailed descriptions of matters that are well known, repeated descriptions of actually identical structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the drawings and the following description are provided so that those skilled in the art can fully understand the present application, and are not intended to limit the subject matter recited in the claims.

[0046] The "ranges" disclosed in the present application are defined in the form of lower and upper limits, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. The ranges defined in this manner can be inclusive or exclusive of the end values, and can be arbitrarily combined, i.e., 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 particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. 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 contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, a numerical range "a-b" indicates a shorthand manner of describing an arbitrarily selected combination of real numbers between "a" and "b", where "a" and "b" are both real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed herein, and "0-5" is merely a shorthand manner of describing these numerical combinations. In addition, when it is stated that a parameter is an integer ≥ 2, it is equivalent to disclose that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0047] All embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0048] All technical features and optional technical features of the present application can be combined with each other to form new technical solutions, if not specifically stated otherwise.

[0049] If not specified otherwise, all steps of the present application can be performed in sequence or randomly, optionally in sequence. For example, the method comprises steps (a) and (b) means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method can further comprise step (c) means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0050] If not specified otherwise, the present application refers to "comprising" and "including" as open terms, which can also be closed terms. For example, "comprising" and "including" can mean that other components not listed can also be included or comprised.

[0051] If not specified otherwise, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, any of the following satisfy the condition "A or B": 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).

[0052] With the popularization of secondary batteries, it is a common pursuit in the industry to replace the metal foil (such as copper foil) commonly used in the prior art with low-cost metals (such as Fe, Zn, Pb, Mg) as the current collector to achieve cost reduction of secondary batteries. However, the above-mentioned low-cost metals have poor corrosion resistance in an electrochemical environment, and the mechanical strength decreases during cyclic use, resulting in wrinkles and even breakage of the current collector during cycling, and the cycle stability of the battery is reduced, which is difficult to meet the market demand for the use of secondary batteries.

[0053] Based on this, the present application provides a current collector which, while achieving cost reduction of secondary batteries, also takes into account the cycle stability of secondary batteries.

[0054] [Secondary battery]

[0055] In one embodiment of the present application, as shown in FIG. 1, 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, the first element includes one or more of Fe, Zn, Pb, and Mg; the surface layer 62 includes a second element, the second element includes one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, and Co, and the bonding strength between the surface layer and the intermediate layer is greater than 100 N / m.

[0056] The layered structure of the pole piece can be tested by any known method in the art. As an example, the pole piece is cut along its thickness, and the elements in the longitudinal section of the pole piece are characterized by using metallographic, scanning electron microscopy, energy spectrum analyzer and other morphology and element analysis instruments. The surface layer refers to the region extending from the surface of the current collector to the thickness direction, and the intermediate layer is adjacent to the surface layer on both sides and is arranged between the surface layers. The element types of each layer can be obtained by energy spectrum analysis of the cross section or surface of each layer of the current collector, and the composition can be uniform or not uniform. The surface layer can be a single layer or can include a multi-layer structure. It should be pointed out that the surface layer and the intermediate layer can be identified by the obvious composition boundary in the cross section of the current collector, and it does not mean that there is also a clear stratification in the cross section morphology.

[0057] In some embodiments, the intermediate layer comprises Fe.

[0058] Iron element has low cost and rich reserves, which can significantly reduce the cost of the pole piece and promote the low cost of the secondary battery. Moreover, iron element has low density compared with copper foil commonly used in the prior art, which is beneficial to weight reduction of the battery and further improvement of the energy density.

[0059] In some embodiments, the intermediate layer comprises at least two first elements.

[0060] In some embodiments, the surface layer comprises one or more of Ni, Cr, Mo, W, Cu.

[0061] Ni, Cr, Mo, W not only can improve the corrosion resistance of the current collector, but also can realize the close packing of the crystal lattice, which is beneficial to improve the strength of the current collector, inhibit the expansion and contraction of the current collector during the process of deintercalating active ions, reduce the risk of wrinkling and even breaking of the pole piece, and improve the cycle life and safety of the secondary battery. Copper element not only can improve the corrosion resistance of the current collector, but also has good electrical conductivity, which can improve the current-carrying capacity of the current collector and improve the electrochemical performance of the secondary battery.

[0062] In some embodiments, the surface layer comprises at least two second elements.

[0063] In some embodiments, the surface layer comprises an alloy composed of Ni and W. In some embodiments, the surface layer comprises an alloy composed of Ni and Cr. In some embodiments, the surface layer comprises an alloy composed of Ni and Mo. In some embodiments, the surface layer comprises an alloy composed of Ni and Sn. In some embodiments, the surface layer comprises an alloy composed of Ni and Cu. In some embodiments, the surface layer comprises an alloy composed of Ni and Bi. In some embodiments, the surface layer comprises an alloy composed of Ni and Co.

[0064] The strength of the current collector can be further improved by alloying at least two second elements, and the cycle life of the secondary battery can be improved.

[0065] The bonding strength between the surface layer and the intermediate layer can be tested by a peeling strength tester according to any known method. As an example, specifically, a high-bonding-strength, W 24 mm wide adhesive tape (such as high-viscosity 3M tape) is tightly attached to the surface of the current collector, and after being rolled back and forth three times by a 2 kg roller, one side of the tape is torn and placed in the upper clamp of the tensile tester, and the current collector is clamped in the lower clamp. The tensile tester is started, and the tape is stretched upward at a rate of 1 mm / min. The average value of the peeling force when the force value in the stretching curve is no longer linearly increasing and enters the fluctuation interval, and the displacement length is greater than 25 mm, is taken as the surface layer peeling force F (unit: N). For samples with a failure mode of surface layer peeling, the bonding strength can be calculated using the formula P=F / W, and the unit is N / m. For samples with a failure mode of tape peeling, it can be determined that the bonding strength between the surface layer and the intermediate layer is greater than the peeling strength of the tape.

[0066] In some embodiments, the bonding strength between the surface layer and the intermediate layer can be selected to be 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 numerical range between any two of them.

[0067] The first element in the intermediate layer is less expensive than the metal foil (such as copper foil) commonly used in the prior art, which can reduce the cost of the secondary battery. Moreover, the metal composed of the first element has high strength, which is beneficial to improve the breaking strength of the current collector, reduce the probability of crimping of the pole piece during the cycle process, reduce the risk of film layer powdering of the pole piece or increasing the polarization of the pole piece due to the growth of the ion diffusion path, and reduce the risk of lithium precipitation of the pole piece during the cycle process. In addition, the surface layer containing the second element is arranged on both sides of the surface of the intermediate layer, which can reduce the corrosion degree of the low-cost element in the intermediate layer in the electrochemical environment, so that the pole piece still maintains good mechanical strength in the electrochemical environment. Although the arrangement of the corrosion-resistant surface layer on the surface of the intermediate layer is beneficial to improve the corrosion resistance of the current collector, the weak bond between the surface layer and the intermediate layer is prone to form cracks during the cycle process, resulting in local primary batteries and accelerating corrosion. Studies have shown that the current collector with a bonding strength between the surface layer and the intermediate layer within the above range can reduce the risk of cracking of the surface layer and the intermediate layer during the cycle process, and the surface layer can effectively protect the intermediate layer during the cycle process, delay the occurrence of corrosion of the intermediate layer, and comprehensively improve the cycle stability of the battery.

[0068] In some embodiments, the intermediate layer comprises 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.

[0069] The mass percentage of the first element based on the total mass of the elements in the intermediate layer can be tested by any known method. As an example, a plurality of regions of the intermediate layer are randomly selected for element analysis by energy spectrum, the selected regions are spaced apart from the surface layer by at least 0.5 μm, the mass percentage of the first element in each region is obtained, and the average of the mass percentage of the first element in at least 10 regions is taken as the mass percentage of the first element in the intermediate layer.

[0070] In some embodiments, the mass percentage of the first element based on the total mass of the elements in the intermediate layer can be selected from 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or any numerical range between any two of them.

[0071] 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.

[0072] The high mass percentage of the first element in the intermediate layer can reduce the cost of the pole piece, and significantly reduce the cost of the secondary battery. The presence of the second element in the intermediate layer can further improve the strength and stability of the pole piece through alloying of at least two elements, and improve the cycle life of the secondary battery.

[0073] In some embodiments, the mass percentage of the first element based on the total mass of the elements in the intermediate layer is 70% to 95%.

[0074] In some embodiments, the surface layer comprises at least one second element and at least one first element, and 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.

[0075] The mass percentage of the second element based on the total mass of the elements in the surface layer can be tested by any known method. Specifically, the mass percentage of the first element in the intermediate layer can be tested by referring to the testing method described above.

[0076] In some embodiments, the second element has a mass percentage of 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or any numerical range between any two of the aforementioned values, based on the total mass of elements in the surface layer.

[0077] The second element with a high mass percentage in the surface layer can balance the low cost, high strength, and stability of the pole piece, so that the secondary battery realizes low cost and long cycle life at the same time.

[0078] In some embodiments, the second element has a mass percentage of 70% to 95%, based on the total mass of elements in the surface layer.

[0079] In some embodiments, the thickness percentage of the intermediate layer is greater than or equal to 50%, and the total thickness percentage of the surface layer is less than or equal to 50%, based on the total thickness of the current collector.

[0080] The thickness percentage of the intermediate layer, based on the total thickness of the current collector, can be tested in any manner known in the art. As an example, the prepared current collector is placed in liquid nitrogen for quenching, 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 the surface layer on one side can be tested using the same or similar method; the total thickness percentage of the surface layer is obtained by adding the thickness of the surface layer on both sides and dividing by the total thickness of the current collector.

[0081] In some embodiments, the thickness percentage of the intermediate layer is 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or any numerical range between any two of the aforementioned values, based on the total thickness of the current collector.

[0082] In some embodiments, the total thickness percentage of the surface layer is 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or any numerical range between any two of the aforementioned values, based on the total thickness of the current collector.

[0083] The current collector with a thickness percentage within the above range can balance the electrochemical stability of the pole piece while reducing costs, and simultaneously realize cost reduction and life improvement of the secondary battery.

[0084] In some embodiments, the thickness percentage of the intermediate layer is 70% to 95%, and the total thickness percentage of the surface layer is 5% to 30%, based on the total thickness of the current collector.

[0085] The current collector with a thickness within the above range can balance the low cost and high cycle life of the secondary battery.

[0086] In some embodiments, the bonding strength between the surface layer and the intermediate layer is 150 N / m to 500 N / m.

[0087] The current collector with the bonding strength between the surface layer and the intermediate layer within the above range can effectively protect the intermediate layer, delay the corrosion of the intermediate layer, and improve the cycle stability of the battery.

[0088] 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, optionally 2.8 to 100, and further optionally 3 to 5.7.

[0089] The average grain size of the surface layer or the intermediate layer can be characterized by X-ray diffraction (XRD) test on different regions of the current collector. The cross section of the current collector is observed, the thickness of the surface layer and the intermediate layer in the current collector is identified, and the sample to be tested is obtained within the range of different thicknesses. As an example, the X-ray diffraction pattern of the current collector sample is obtained by an X-ray diffractometer with CuKα ray as the ray source, and the average grain size is calculated by the Scherrer formula D = Kλ / (βcosθ), wherein D is the average grain size, K is a constant, λ is the X-ray wavelength, the wavelength is 0.154 nm, β is the half-height width of the diffraction peak, and θ is the diffraction angle. In order to enhance the comparability of the data, the same crystal face diffraction angle 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 face is selected for grain size calculation.

[0090] In some embodiments, the ratio of the average grain size of the surface layer to the average grain size of the intermediate layer is optionally 1.96, 2, 2.8, 3, 4, 4.7, 5, 5.7, 10, 20, 30, 40, 50, 100, or any numerical range between any two of them.

[0091] The ratio of the average grain size of the surface layer to the average grain size of the intermediate layer within the above range indicates that the intermediate layer has fewer grain boundaries than the surface layer, which is beneficial to reduce the proportion of grain boundaries in the surface layer, delay the probability of large-area corrosion of the intermediate layer caused by intergranular corrosion of the current collector, further improve the corrosion resistance of the low-cost current collector, and improve the cycle life of the battery.

[0092] In some embodiments, as shown in FIG. 2, the surface layer 62 includes a first surface layer 62-1 close to the intermediate layer 61 and a second surface layer 62-2 arranged on the side of the first surface layer 62-1 away from the intermediate layer 61, and the first surface layer 62-1 and the second surface layer 62-2 each independently comprise at least one second element.

[0093] It can be understood that 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.

[0094] In some embodiments, the second element in the first surface layer is different from the second element in the second surface layer.

[0095] Through the multi-layer design of the surface layer, the customized design of the pole piece performance can be realized, and the synchronous improvement of the performance of the pole piece including tensile strength, elongation at break, chemical stability, etc. is considered.

[0096] In some embodiments, the first surface layer comprises Ni, and the second surface layer comprises Cu.

[0097] The pole piece has good strength and ductility at the same time, and can comprehensively improve the cycle life of the secondary battery.

[0098] In some embodiments, the thickness of the current collector is 2 μm to 20 μm. In some embodiments, the thickness of the current collector can be selected to be 4 μm to 10 μm.

[0099] In some embodiments, the thickness of the current collector can be selected to be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any numerical range between any two of them.

[0100] In some embodiments, 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%.

[0101] 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 can be tested by any known method in the art. As an example, the element composition and content of the current collector are tested by an inductively coupled plasma spectrometer (ICP).

[0102] 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 to be 95%, 96%, 97%, 98%, 99%, 99.5%, 99.9%, 100%, or any numerical range between any two of them.

[0103] In some embodiments, the tensile fracture strength of the current collector is 400 MPa-1600 MPa, and / or the elongation at break of the current collector is 2%-10%.

[0104] In some embodiments, the tensile fracture strength of the current collector can be selected from 400 MPa, 500 MPa, 600 MPa, 700 MPa, 800 MPa, 900 MPa, 1000 MPa, 1100 MPa, 1200 MPa, 1300 MPa, 1400 MPa, 1500 MPa, 1600 MPa, or any numerical range between any two of them.

[0105] In some embodiments, the elongation at break of the current collector can be selected from 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any numerical range between any two of them.

[0106] The tensile fracture strength and the elongation at break of the current collector can be tested in a manner known in the art. As an example, the current collector is cut into a sample with a length of 150 mm and a width of 15 mm, and the tensile test is performed on the sample using a tensile testing machine (e.g., INSTRON 3343) at a tensile speed of 5 mm / min with a gauge length of 50 mm, and the tensile fracture strength of the sample is calculated as the maximum tensile force in the tensile curve divided by the area, and the elongation at break is calculated as the ratio of the elongation at break to the length before stretching; 10 parallel tests are performed for each sample, and the average value is calculated as the tensile fracture strength and the elongation at break of the sample.

[0107] In some embodiments, the tensile fracture strength of the current collector is 500 MPa-1200 MPa, and / or the elongation at break of the current collector is 5%-8%.

[0108] The current collector has both excellent tensile fracture strength and good elongation at break, which is beneficial to improve the cycle life of the secondary battery.

[0109] 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.

[0110] The preparation method of the intermediate layer can further reduce the manufacturing cost of the pole piece, and realize the low cost of the secondary battery. The above preparation method of the surface layer can improve the bonding strength between the surface layer and the intermediate layer, and improve the cycle life of the secondary battery.

[0111] In some embodiments, the surface layer is deposited on the intermediate layer after surface corrosion of the intermediate layer.

[0112] Depositing the surface layer after surface corrosion of the intermediate layer is beneficial to improve the bonding strength between the intermediate layer and the surface layer, reduce the risk of corrosion of the current collector, and improve the cycle life of the secondary battery.

[0113] The second aspect of the present application provides a secondary battery, the secondary battery comprising a negative electrode tab, the negative electrode tab comprising the current collector of the first aspect and a negative electrode film layer disposed on at least one side of the current collector.

[0114] In the prior art, the current collector in the negative electrode tab is mostly copper foil, and this component accounts for nearly 10% of the total cost of the secondary battery. The current collector in the embodiments of the present application can significantly reduce the cost of the secondary battery, and at the same time improve the cycle life of the secondary battery.

[0115] In some embodiments, the film layer comprises a negative electrode active material, which comprises 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.

[0116] In some embodiments, the negative electrode active material comprises a silicon-based material, which comprises one or more of nanosilicon, silicon-carbon materials, silicon-oxygen materials, silicon-nitrogen materials, and silicon alloys.

[0117] Silicon-based materials are beneficial to improving the energy density of the secondary battery, but the silicon-based materials have a large expansion rate during the cycle of the secondary battery, which easily leads to the risk of cracking or even breaking of the current collector. The secondary battery of the embodiments of the present application is particularly suitable for battery systems comprising silicon-based materials, and is beneficial to the secondary battery to have good cycle life and safety performance under high energy density.

[0118] In some embodiments, the negative electrode film layer can further optionally comprise a negative electrode conductive agent. The present application does not have a particular limitation on the type of the negative electrode conductive agent, and as an example, the negative electrode conductive agent can comprise one or more of super conductive carbon, conductive graphite, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] In some embodiments, the negative electrode film layer can further optionally comprise a negative electrode binder. The present application does not have a particular limitation on the type of the negative electrode binder, and as an example, the negative electrode binder can comprise one or more of styrene butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (for example, polyacrylic acid PAA, polymethylacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0120] In some embodiments, the negative electrode film layer can further optionally comprise other auxiliary agents. As an example, the other auxiliary agents can comprise thickening agents, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, and the like.

[0121] The negative electrode film layer is usually formed by coating a negative electrode slurry on a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is usually formed by dispersing a negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring uniformly. The solvent can be N-methyl pyrrolidone (NMP) or deionized water, but is not limited thereto.

[0122] The negative electrode tab does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode tab described in the present application further includes a conductive primer layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer; in some embodiments, the negative electrode tab described in the present application further includes a protective layer covering the surface of the negative electrode film layer.

[0123] [Positive electrode tab]

[0124] In some embodiments, the secondary battery includes a positive electrode tab.

[0125] The positive electrode tab includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, the positive electrode film layer including the positive electrode active material of the first aspect of the present application, and the current collector being the battery aluminum foil of the present application. The battery aluminum foil of the present application can effectively improve the brittleness of the battery tab and improve the anti-creasing ability of the aluminum foil when applied to a secondary battery.

[0126] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as a metal foil, the battery aluminum foil of the present application is used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming the battery aluminum foil of the present application on a polymer material base material such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), or the like.

[0127] In some embodiments, the positive active material can employ a positive active material for a battery known in the art. As an example, the positive active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive active material for a battery can also be used. These positive active materials can be used alone only one kind, or two or more kinds in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(also referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2(also referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2(also referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(also referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2(also referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and a modified compound thereof, etc. Examples of the lithium-containing phosphate of an olivine structure can include, but are not limited to, at least one of lithium iron phosphate (e.g., LiFePO4(also referred to simply as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0128] In some embodiments, the positive electrode film layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluorotetrafluoroethylene-propylene terpolymer, a vinylidene-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0129] In some embodiments, the positive electrode film layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode tab can be prepared by dispersing the components used to prepare the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector; and subjecting the positive electrode slurry to drying, cold pressing, and the like to obtain the positive electrode tab.

[0131] [Electrolyte]

[0132] In some embodiments, the secondary battery includes an electrolyte.

[0133] The electrolyte functions to conduct ions between the positive electrode tab and the negative electrode tab. The type of electrolyte is not particularly limited in the present application and can be selected as desired. For example, the electrolyte can be liquid, gel, or all-solid.

[0134] In some embodiments, the electrolyte employs an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0135] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro oxalate borate, lithium di-oxalate borate, lithium difluoro di-oxalate phosphate, and lithium tetrafluoro oxalate phosphate.

[0136] In some embodiments, the solvent can 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, butylene 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.

[0137] In some embodiments, the electrolyte solution can also optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can also include an additive that improves certain properties of the battery, such as an additive that improves overcharge performance of the battery, an additive that improves high-temperature or low-temperature performance of the battery, and the like.

[0138] [Separator]

[0139] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous separator having good chemical stability and mechanical stability can be used.

[0140] In some embodiments, the separator can be made of at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the layers can be the same or different, and are not particularly limited.

[0141] The third aspect of the present application provides an electric device including the secondary battery of any of the embodiments.

[0142] Generally, the secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging of the battery, active ions are inserted into and extracted from the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, and functions to prevent short circuiting between the positive electrode and the negative electrode, while allowing ions to pass through.

[0143] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to make an electrode assembly by a roll-pressing process or a stacking process.

[0144] In some embodiments, the secondary battery can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte.

[0145] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, etc. can be listed.

[0146] The shape of the secondary battery is not particularly limited in the present application, and the secondary battery can be cylindrical, square, or any other shape. For example, FIG. 3 is a square structure of a secondary battery 5 as an example.

[0147] In some embodiments, referring to FIG. 4, the outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, which enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode tab, the negative electrode tab, and the separator film can be wound or stacked to form an electrode assembly 52. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, which can be selected by those skilled in the art according to specific actual needs.

[0148] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0149] FIG. 5 is a battery module 4 as an example. Referring to FIG. 5, in the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0150] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0151] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0152] FIGS. 6 and 7 are a battery pack 1 as an example. Referring to FIGS. 4 and 5, the battery pack 1 can include a battery box and a plurality of battery modules 6 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0153] In addition, the present application also provides a power consuming device including at least one of the secondary battery, the battery module, or the battery pack provided by the present application. The secondary battery, the battery module, or the battery pack can be used as a power source of the power consuming device, or can be used as an energy storage unit of the power consuming device. The power consuming device can include a mobile device (such as a mobile phone, a notebook computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto.

[0154] As the power consuming device, a secondary battery, a battery module, or a battery pack can be selected according to the use requirement thereof.

[0155] Fig. 8 is a power consuming device as an example. The power consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power consuming device, a battery pack or a battery module can be used.

[0156] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thin and light, and a secondary battery can be used as the power source.

[0157] Embodiment

[0158] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application only and are not to be understood as a limitation of the present application. In the embodiments, the specific techniques or conditions not mentioned are performed according to the techniques or conditions described in the literature in the art or according to the product manual. The reagents or instruments not mentioned the manufacturer are all conventional products that can be obtained commercially.

[0159] Embodiment 1

[0160] (1) Preparation of the current collector

[0161] Preparation of the intermediate layer:

[0162] A stainless steel plate is used as the cathode, and a soluble iron plate is used as the anode. The plating solution formula is iron chloride 600 g / L, calcium chloride 300 g / L, hydrochloric acid 0.5 g / L. The current density is 10 A / dm 2 The pH is adjusted to 1.2-1.5, and the plating temperature is 90°C. The iron foil is obtained by electroplating. After the preparation of the iron foil is completed, the iron foil is activated in a 5% dilute sulfuric acid environment to remove the oxide layer. The activation time is 30 s, and the thickness is 4 μm.

[0163] Preparation of the surface layer:

[0164] The intermediate layer prepared above is used as the cathode, and a titanium-iridium alloy plate is used 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, and polydithiobispropane sulfonic acid sodium (SPS) 5 mg / L. The current density is 10 A / dm 2 The plating temperature is room temperature 25±5°C. The copper layer is plated on both sides of the intermediate layer. The thickness of the Cu layer on each side is 0.5 μm.

[0165] (2) Preparation of the positive electrode sheet

[0166] The positive electrode active material NCM811, the conductive agent carbon black, and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 96:2:2 in an N-methyl pyrrolidone (NMP) solution to prepare a positive electrode slurry, which is then coated on the surface of an aluminum foil using an extrusion coater and dried to obtain a positive electrode film layer. The positive electrode film layer is then cold-pressed using a cold press to obtain a final positive electrode tab. The areal density of the single-sided film layer of the positive electrode tab is 400 mg / 1540.25 mm 2 ; and the tap density of the positive electrode tab is 3.4 g / cm 3 .

[0167] (3) Preparation of the negative electrode tab

[0168] The negative electrode active material (a mixture of 30% by mass of a silicon-carbon composite material and 70% by mass of graphite), the conductive agent carbon black, the binder styrene-butadiene rubber (SBR), and the thickening agent sodium hydroxymethyl cellulose (CMC) are mixed in a mass ratio of 93.5:1.8:3.5:1.2 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry is coated on the prepared current collector, and after drying and other processes, a negative electrode is obtained. The areal density of the single-sided film layer of the negative electrode tab is 93.7 mg / 1540.25 mm 2 ; and the tap density of the negative electrode tab is 1.3 g / cm 3 .

[0169] (4) Isolation film

[0170] A polyethylene separator is used as the isolation film.

[0171] (5) Electrolyte

[0172] Ethylene carbonate, methyl ethyl carbonate, and diethyl carbonate are mixed in a volume ratio of 1:1:1 to obtain an organic solvent. A fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0173] (6) Battery assembly

[0174] The above positive electrode tab, isolation film, and negative electrode tab 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 packaging, standing, formation, shaping, and other processes, a lithium ion secondary battery is obtained.

[0175] Example 2

[0176] Example 2 is basically the same as Example 1, except that the preparation method of the surface layer is different. Specifically, the surface layer is prepared as follows:

[0177] The foil prepared above is used as cathode, and a titanium-iridium alloy plate is used as anode. The plating solution formula is: nickel sulfate 200 g / L, sodium chloride 5 g / L, boric acid 30 g / L, and sodium dodecyl sulfonate 0.1 g / L. The current density is 1-1.5 A / dm 2 The pH is adjusted to 4-4.5, and the plating temperature is 45°C. A nickel layer is plated on both sides of the foil. The thickness of the surface layer on each side is 1 μm.

[0178] Example 3

[0179] Example 3 is basically the same as Example 2, except that the preparation method of the surface layer is different. Specifically, the preparation of the surface layer is as follows:

[0180] The foil prepared above is used as cathode, and a titanium-iridium alloy plate is used as anode. The plating solution formula is: nickel sulfate 200 g / L, sodium chloride 5 g / L, boric acid 30 g / L, and sodium dodecyl sulfonate 0.1 g / L. The current density is 1-1.5 A / dm 2 The pH is adjusted to 4-4.5, and the plating temperature is 45°C. A nickel layer is plated on both sides of the foil. The thickness of the surface layer on each side is 1 μm.

[0181] Example 4

[0182] Example 4 is basically the same as Example 2, except that the preparation method of the surface layer is different. Specifically, the preparation of the surface layer is as follows:

[0183] The foil prepared above is used as cathode, and a titanium-iridium alloy plate is used as anode. The plating solution formula is: nickel sulfate 200 g / L, sodium chloride 5 g / L, boric acid 30 g / L, and sodium dodecyl sulfonate 0.1 g / L. The current density is 1-1.5 A / dm 2 The pH is adjusted to 4-4.5, and the plating temperature is 45°C. A nickel layer is plated on both sides of the foil. The thickness of the surface layer on each side is 1 μm.

[0184] Example 5

[0185] Example 5 is basically the same as Example 2, except that the preparation method of the surface layer is different. Specifically, the preparation of the surface layer is as follows:

[0186] The foil prepared above is used as cathode, and a titanium-iridium alloy plate is used as anode. The plating solution formula is: nickel sulfate 200 g / L, sodium chloride 5 g / L, boric acid 30 g / L, and sodium dodecyl sulfonate 0.1 g / L. The current density is 1-1.5 A / dm 2 The pH is adjusted to 4-4.5, and the plating temperature is 45°C. A nickel layer is plated on both sides of the foil. The thickness of the surface layer on each side is 1 μm.

[0187] Example 6

[0188] Example 6 is basically the same as Example 2, except that the preparation method of the intermediate layer is different, specifically, the preparation of the intermediate layer is:

[0189] A stainless steel plate is used as the cathode, and a soluble iron plate is used as the anode. The plating solution formula is ferrous sulfate 70 g / L, sodium molybdate 94 g / L, sodium citrate 230 g / L, the current density is 0.5-1 A / dm 2 , the pH is adjusted to 4-5, and the electroplating temperature is 30°C. The iron-molybdenum alloy foil with a thickness of 5 μm is obtained by electroplating.

[0190] Example 7

[0191] Example 7 is basically the same as Example 2, except that the preparation method of the intermediate layer is different, specifically, the preparation of the intermediate layer is:

[0192] A stainless steel plate is used as the cathode, and a soluble iron plate is used as the anode. The plating solution formula is 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 is 5 A / dm2, the rotation speed is 500 rpm / min, the pH is adjusted to 2.5-3, and the electroplating temperature is 55°C. The iron-nickel alloy foil with a thickness of 5 μm is obtained by electroplating.

[0193] Example 8

[0194] Example 8 is basically the same as Example 2, except that the electroplating time of the Fe foil is extended, and the electroplating time of the two sides of the plating layer is reduced, so that the thickness of the intermediate layer is 5.8 μm, accounting for 97% of the thickness of the current collector; the thickness of the surface layer on both sides is 0.1 μm, accounting for 3% of the thickness of the current collector.

[0195] Example 9

[0196] Example 9 is basically the same as Example 3, except that the preparation method of the surface layer is adjusted,

[0197] The foil material prepared above is used as the cathode, and a titanium-iridium alloy plate is used 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, the current density is 4 A / dm 2 , the pH is adjusted to 3.5-4, and the electroplating temperature is 55°C. A first surface layer of nickel-iron alloy is plated on both sides of the foil; the thickness of the first surface layer is 0.5 μm; a copper layer is 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 is 1 μm.

[0198] Example 10

[0199] Example 10 was prepared in the same manner as Example 2, except that the activation time of the iron foil was adjusted to 10 seconds, thereby adjusting the interlayer adhesion strength between the surface layer and the intermediate layer.

[0200] Example 11

[0201] Example 11 was prepared in the same manner as Example 1, except that the current density during the preparation of the surface layer was adjusted to 1 A / dm 2 , thereby adjusting the ratio of the average grain size between the surface layer and the intermediate layer.

[0202] Comparative Example 1

[0203] Comparative Example 1 was prepared in the same manner as Example 1, except that a commercially available copper foil was used as the negative current collector.

[0204] Comparative Example 2

[0205] Comparative Example 2 was prepared in the same manner as Example 1, except that a commercially available iron foil was used as the negative current collector.

[0206] Performance Test

[0207] (1) Corrosion Resistance Test of the Current Collector

[0208] The current collector was punched into a 14 mm diameter disc as the cathode, and a lithium sheet was used as the anode to assemble a coin cell. The coin cell was charged at a constant voltage of 4.5 V for 7 days, and the voltage drop time was recorded when the voltage reached 4.5 V.

[0209] (2) Cycle Capacity Retention Rate of the Battery

[0210] At 25°C, the battery was charged to 4.25 V at a rate of 0.5C and then discharged to 2.5 V at a rate of 0.5C, which was one cycle. The discharge capacity of the first cycle was recorded as C0, and the discharge capacity after 1000 cycles was recorded as C1000. The cycle capacity retention rate of the battery was calculated as C1000 / C0.

[0211] (3) Estimated Cost

[0212] The cost of the current collector in the examples was estimated based on the cost of the general-purpose copper foil in Comparative Example 1, which was taken as 100%.

[0213] Table 1

[0214] Table 2

[0215] Table 3

[0216] Table 4

[0217] Table 5

[0218] It can be seen from the comparison of the examples and the comparative examples that the current collector comprises a surface layer and an intermediate layer arranged between the surface layer, the intermediate layer comprises a first element, the first element comprises one or more of Fe, Zn, Pb, Mg, and Al; the surface layer comprises a second element, the second element comprises one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, and Co, which can reduce the cost of the secondary battery while improving the strength of the secondary battery and improving the cycle life of the secondary battery.

[0219] It can be seen from Table 2 that the current collector provided by the examples has better pressure durability than the pure iron current collector, indicating that it has better corrosion resistance in an electrochemical environment.

[0220] It can be seen from Table 3 that the surface layer comprises a first surface layer close to the intermediate layer and a second surface layer arranged on the side of the first surface layer away from the intermediate layer, the first surface layer comprises nickel, and the second surface layer comprises copper, which can improve the elongation at break of the current collector while enhancing the cycle life of the secondary battery.

[0221] The bonding strength between the surface layer and the intermediate layer is greater than 100 N / m. It can be seen from Table 4 that the bonding strength between the surface layer and the intermediate layer is greater than or equal to 150 N / m, which is conducive to improving the bonding performance of the intermediate layer and the surface layer, delaying the time of corrosion of the intermediate layer, and further improving the corrosion resistance of the low-cost current collector.

[0222] It can be seen from Table 5 that 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 is conducive to reducing the proportion of grain boundaries of the surface layer, delaying the probability of large-area corrosion of the intermediate layer caused by intergranular corrosion of the current collector, further improving the corrosion resistance of the low-cost current collector, and comprehensively improving the cycle life of the battery.

[0223] It should be noted that the present application is not limited to the described embodiments. The described embodiments are only examples, and embodiments having the same technical idea and playing the same role and effect within the scope of the technical solutions of the present application are all included in the technical scope of the present application. In addition, within the scope of the main idea of the present application, various modifications of the embodiments that can be thought of by those skilled in the art, and other ways constructed by combining part of the elements in the embodiments are also included in the scope of the present application.

Claims

1. A current collector characterized by comprising: The current collector comprises 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, Mg; the surface layer comprises a second element, the second element comprising one or more of Ni, Cr, Mo, Sn, Cu, Bi, W, Co; the bonding strength between the surface layer and the intermediate layer is greater than 100 N / m.

2. The current collector of claim 1, wherein The intermediate layer comprises 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 of claim 2, wherein The mass percentage of the first element is 70% to 95% based on the total mass of the elements in the intermediate layer.

4. The current collector according to any one of claims 1 to 3, characterized in that, The surface layer comprises at least one second element and at least one first element, and 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.

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

6. The current collector according to any one of claims 1 to 5, wherein The thickness percentage of the intermediate layer is greater than or equal to 50% based on the total thickness of the current collector, and the total thickness percentage of the surface layer is less than or equal to 50%.

7. The current collector of any one of claims 1 to 6, wherein, The thickness percentage of the intermediate layer is 70% to 95% based on the total thickness of the current collector, and the total thickness percentage of the surface layer is 5% to 30%.

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

9. The current collector of any one of claims 1 to 8, wherein, 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, optionally 2.8 to 100, and further optionally 3 to 5.

7.

10. The current collector of any one of claims 1 to 9, wherein, The surface layer comprises 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, and the first surface layer and the second surface layer each independently comprise at least one second element.

11. The current collector of any one of claims 1 to 10, wherein, The thickness of the current collector is 2 μm to 20 μm, optionally 4 μm to 10 μm.

12. The current collector of any one of claims 1 to 11, wherein, The total mass percentage of the first element and the second element in the current collector is greater than or equal to 95% based on the total mass of the elements in the current collector.

13. The current collector of any one of claims 1 to 12, wherein, The tensile breaking strength of the current collector is 400 MPa to 1600 MPa, and / or the breaking elongation of the current collector is 2% to 10%.

14. The current collector of any one of claims 1 to 13, wherein, The tensile breaking strength of the current collector is 500 MPa to 1200 MPa, and / or the breaking elongation of the current collector is 5% to 8%.

15. The current collector of any one of claims 1 to 14, wherein, 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 of any one of claims 1 to 15, wherein, The surface layer is deposited on the intermediate layer after surface corrosion of the intermediate layer.

17. A secondary battery characterized by comprising: The secondary battery comprises a negative electrode sheet comprising the current collector of 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 by The negative electrode film layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material, and the silicon-based material comprises one or more of nano-silicon, silicon-carbon material, silicon-oxygen material, silicon-nitrogen material, and silicon alloy.

19. An electric device comprising the secondary battery according to claim 17 or 18.

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