Current collector, secondary battery, electric device and preparation method of current collector

Abstract

The invention provides a current collector, a secondary battery, an electric device and a preparation method of the current collector. The current collector comprises surface layers and a middle layer arranged between the surface layers, the middle layer comprises a first metal element, the total mass content of the first metal element is larger than or equal to 80% based on the total mass of the elements of the middle layer, the surface layer comprises a second metal element, and the total mass content of the second metal element is larger than or equal to 80% based on the total mass of the elements of the surface layer. The total mass content of the second metal element is greater than or equal to 80%; the tensile strength of the middle layer is larger than or equal to that of the surface layer, the bending resistance of the surface layer is larger than or equal to that of the middle layer, and the diffraction intensity of a crystal face (111) in the surface layer accounts for 20%-40% of the sum of the diffraction intensity of the crystal face (111), the crystal face (200), the crystal face (220), the crystal face (311) and the crystal face (222) in the surface layer.

Description

[0001] This application is a divisional application based on the invention with application number 202411124874.8, application date August 15, 2024, applicant CATL, and invention title "Current collector, secondary battery, power supply device and method for preparing current collector". Technical Field

[0002] This application belongs to the field of battery technology, specifically relating to a current collector, a secondary battery, an electrical device, and a method for preparing the current collector. Background Technology

[0003] 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.

[0004] Current collectors are an important component of rechargeable batteries. Improving the energy density of rechargeable batteries often comes at the cost of reduced cycle life, highlighting the urgent need to develop current collectors that balance energy density and cycle life to meet the requirements of next-generation rechargeable batteries. Summary of the Invention

[0005] This application is made in view of the above-mentioned problems, and its purpose is to provide a current collector that can simultaneously take into account battery energy density and cycle life.

[0006] A first aspect of this application provides a current collector comprising a surface layer and an intermediate layer disposed between the surface layers. The intermediate layer comprises a first metal element, and the total mass content of the first metal element is greater than or equal to 80% based on the total mass of the intermediate layer elements. The surface layer comprises a second metal element, and the total mass content of the second metal element is greater than or equal to 80% based on the total mass of the surface layer elements. The tensile strength of the intermediate layer is greater than or equal to the tensile strength of the surface layer, and the bending resistance of the surface layer is greater than or equal to the bending resistance of the intermediate layer.

[0007] This current collector achieves a balance between strength and bending resistance through a multi-layer design. The middle layer has relatively high tensile strength, while the surface layer has relatively high bending resistance. This improves the bending resistance of the current collector while maintaining its high strength, delaying the time for the electrode to crack during the cycle of the secondary battery, thus increasing the cycle life of the secondary battery and reducing safety risks.

[0008] In any embodiment, the first metallic element includes one or more of Fe, Sn, Ni, and Zn.

[0009] Metal materials with the aforementioned first metallic element as the main component often have high strength, which is beneficial for improving the tensile strength of the current collector, delaying the time when cracks appear on the outer ring of the electrode during cycling, and thus improving the cycle life of the battery.

[0010] In any embodiment, the second metallic element includes Cu.

[0011] Copper metal materials often have high ductility, which helps improve the bending resistance of the current collector and delays the time when cracks appear in the inner ring of the electrode during cycling, thus improving the cycle life of the battery.

[0012] In any embodiment, the average grain size of the surface layer is greater than or equal to 1.7 μm.

[0013] Surface layers with an average grain size within the above range can improve the bending resistance of the current collector and delay the time when cracks appear in the inner ring of the cell during cycling.

[0014] In any embodiment, the average grain size of the surface layer is 1.7 μm to 3.5 μm.

[0015] In any embodiment, the average grain size of the surface layer is 1.9 μm to 2.5 μm.

[0016] Surface layers with an average grain size within the above range can better balance the strength and bending resistance of the current collector, delay the time when the cell cracks during cycling, improve the cycle life of the secondary battery, and reduce safety risks.

[0017] In any embodiment, the diffraction intensity of the (111) crystal plane in the surface layer accounts for 20%-40% of the total diffraction intensity of the (111) crystal plane, (200) crystal plane, (220) crystal plane, (311) crystal plane, and (222) crystal plane in the surface layer.

[0018] This application embodiment improves the bending resistance of the current collector by controlling the diffraction intensity ratio of the (111) crystal plane to 20%-40%, thereby achieving a balance between the strength and bending resistance of the current collector, improving the cycle life of the secondary battery, and reducing safety risks.

[0019] In any embodiment, the diffraction intensity of the (111) crystal plane in the surface layer accounts for 25% to 35% of the total diffraction intensity of the (111) crystal plane, (200) crystal plane, (220) crystal plane, (311) crystal plane, and (222) crystal plane in the surface layer.

[0020] The diffraction intensity ratio of the (111) crystal plane in the surface layer within the above range can further balance the strength and bending resistance of the current collector, comprehensively improve the cycle life of the secondary battery, and reduce safety risks.

[0021] In any embodiment, the average grain size of the intermediate layer is 0.1 μm-1 μm.

[0022] Current collectors with an average grain size in the intermediate layer within the above range have higher strength, which can reduce the probability of cracks appearing on the outer ring of wound cells and on the edges of laminated cells.

[0023] In any embodiment, the thickness of the current collector is 3μm-8μm.

[0024] This current collector has a low thickness, which enables effective weight reduction of the battery and is conducive to further improving the battery's energy density.

[0025] In any embodiment, the thickness of the intermediate layer is 2μm to 6μm, and the thickness of the surface layer on one side is 0.5μm to 2μm.

[0026] Current collectors with thicknesses of the intermediate layer and the surface layer within the above-mentioned range can effectively balance the strength and bending resistance of the current collector, improve the cycle life of the secondary battery, and enhance the safety of the secondary battery.

[0027] In any embodiment, under test conditions of room temperature, sample thickness of 6±0.2μm, and tensile speed of 50±0.5mm / min, the tensile strength of the current collector is greater than or equal to 900MPa.

[0028] The aforementioned current collector has high strength, which can improve the cell's resistance to expansion, increase the battery's cycle life, and improve the battery's safety performance.

[0029] In any embodiment, under test conditions of room temperature, sample thickness of 6±0.2μm, and tensile speed of 50±0.5mm / min, the tensile strength of the current collector is greater than or equal to 1000MPa.

[0030] Current collectors with a tensile strength of 1000 MPa or higher can reduce the risk of premature cracking at the outer ring or edge of the cell under expansion force during battery cycling, thus further improving battery safety.

[0031] In any embodiment, under test conditions of room temperature, sample thickness of 6±0.2μm, and tensile speed of 50±0.5mm / min, the tensile strength of the current collector is 1000MPa-1250MPa.

[0032] Current collectors with tensile strength within the above range can balance strength and bending resistance, thus comprehensively improving the cycle life of the battery.

[0033] In any embodiment, under test conditions of room temperature and a sample thickness of 6±0.2μm, the current collector can be bent more than or equal to 7 times.

[0034] The aforementioned current collector has good bending resistance, which can reduce the probability of premature cracking at the bending points inside the cell, leading to battery failure and improving the cycle life of the battery.

[0035] In any embodiment, under test conditions of room temperature and a sample thickness of 6±0.2μm, the current collector can be bent 7 to 18 times.

[0036] Current collectors with a bending life within the above range can balance bending resistance and strength, thus comprehensively improving the cycle life of the battery.

[0037] A second aspect of this application provides a secondary battery including an electrode, said electrode including a current collector as described in the first aspect.

[0038] A third aspect of this application provides an electrical device including the secondary battery of the second aspect.

[0039] A fourth aspect of this application provides a method for preparing a current collector, the method specifically comprising: obtaining an intermediate layer, the intermediate layer comprising a first metal element, wherein the mass content of the first metal element is greater than or equal to 80% based on the total mass of the intermediate layer elements; depositing a surface layer on the surface of the intermediate layer to obtain a current collector; the surface layer comprising a second metal element, wherein the mass content of the second metal element is greater than or equal to 80% based on the total mass of the surface layer elements; the tensile strength of the intermediate layer is greater than or equal to the tensile strength of the surface layer, and the bending resistance of the surface layer is greater than or equal to the bending resistance of the intermediate layer.

[0040] This current collector achieves a balance between strength and bending resistance through a multi-layer design. The middle layer has relatively high tensile strength, while the surface layer has relatively high bending resistance. This improves the bending resistance of the current collector while maintaining its high strength, delaying the time for the electrode to crack during the cycle of the secondary battery, thus increasing the cycle life of the secondary battery and reducing safety risks.

[0041] In any embodiment, the surface layer is deposited on the surface of the intermediate layer by electroplating. The electroplating method specifically includes applying an electric current to an electroplating solution to reduce and deposit copper ions in the electroplating solution, thereby forming a surface layer on the surface of the intermediate layer.

[0042] In any embodiment, the electroplating solution includes additives, which include one or more of leveling agents, wetting agents, and brighteners.

[0043] In any embodiment, the additive includes a leveling agent, a wetting agent, and a brightening agent.

[0044] The above three additives can be combined to prepare a surface layer that gives the current collector both strength and bending resistance.

[0045] In any embodiment, the concentration of the leveling agent in the electroplating solution is 40 mg / L-80 mg / L.

[0046] In any embodiment, the concentration of the wetting agent in the electroplating solution is 30 mg / L-80 mg / L.

[0047] Wetting agents with concentrations within the above range in the electroplating solution are beneficial for depositing copper grains of appropriate size on the surface layer, balancing the strength and bending resistance of the current collector, and improving the cycle life of the secondary battery.

[0048] In any embodiment, the concentration of chloride ions in the electroplating solution is 30 mg / L-60 mg / L.

[0049] In any embodiment, the concentration of copper ions in the electroplating solution is 50 g / L to 100 g / L.

[0050] In any embodiment, the concentration of the brightener in the electroplating solution is 10 mg / L-25 mg / L.

[0051] In any embodiment, the total mass concentration of the leveling agent and the brightening agent in the electroplating solution is less than 100 mg / L.

[0052] Leveling agents and brighteners with concentrations within the above range in the electroplating solution are beneficial for depositing copper grains of appropriate size on the surface layer, taking into account both the strength and bending resistance of the current collector, and improving the cycle life of the secondary battery.

[0053] In any embodiment, the electroplating temperature is 50±5℃.

[0054] In any embodiment, the pH of the electroplating solution is 4-7.

[0055] In any embodiment, the leveling agent includes one or more of gelatin and Janus Green; the wetting agent includes one or more of hydroxyethyl cellulose and polyethylene glycol; and the brightening agent includes one or more of sodium dithiodipropane sulfonate, sodium 3-mercapto-1-propane sulfonate, and thiourea.

[0056] In any embodiment, the electroplating solution includes gelatin with a concentration of 40 mg / L-80 mg / L, hydroxyethyl cellulose with a concentration of 30 mg / L-80 mg / L, sodium polydisulfide dipropane sulfonate with a concentration of 10 mg / L-25 mg / L, copper ions with a concentration of 50 g / L-100 g / L, and chloride ions with a concentration of 30 mg / L-60 mg / L.

[0057] In any embodiment, the current density of the direct current is 4000 A / m. 2 -8000A / m 2 The electroplating process takes 0.5 to 3 minutes.

[0058] In any embodiment, the preparation method further includes: heat-treating the current collector to obtain an annealed current collector.

[0059] After annealing, the grain size in the current collector increases further, and the intensity ratio of the diffraction peak of the (111) crystal plane decreases further, which is conducive to further improving the bending resistance of the current collector, achieving a balance between the strength and bending resistance of the current collector, and comprehensively improving the cycle life of the secondary battery. Attached Figure Description

[0060] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0061] Figure 1 This is a schematic diagram of the current collector structure according to one embodiment of this application; Figure 2 This is an inverse pole figure of the electron backscatter diffraction image of the current collector surface according to an embodiment of this application; Figure 3 This is an X-ray diffraction pattern of a current collector according to an embodiment of this application; Figure 4 This is a schematic diagram of one embodiment of the secondary battery of this application; Figure 5 This is an exploded view of one embodiment of the secondary battery of this application; Figure 6 This is a schematic diagram of one embodiment of the battery module of this application; Figure 7 This is a schematic diagram of one embodiment of the battery pack of this application; Figure 8 yes Figure 7 An exploded view of an embodiment of the battery pack shown; Figure 9 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.

[0062] In the accompanying drawings, the figures may not be drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Secondary battery, 51 Housing, 52 Electrode assembly, 53 Cover plate, 6 Current collector; 61 Intermediate layer; 62 Surface layer. Detailed Implementation

[0063] The following detailed description, with appropriate reference to the accompanying drawings, discloses embodiments of the current collector, secondary battery, power supply device, and method for preparing the current collector according to 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 for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0064] 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 expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are 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 "ab" 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.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0067] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably 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.

[0068] 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.

[0069] 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).

[0070] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0071] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0072] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0073] In this application, the terms "multiple" or "various" refer to two or more kinds.

[0074] With the increasing energy density of rechargeable batteries, there is a growing demand for thinner and lighter electrode current collectors. As the thickness of the current collector decreases, the maximum tensile load it can withstand drops, making it difficult for current collectors of conventional strength to meet the performance requirements of rechargeable batteries during long cycles. With the increase in cycle count, the reciprocating expansion of the electrode makes wound cells using existing ordinary strength current collectors prone to cracking at the outermost ring where the expansion force is greatest, leading to electrode breakage, resulting in a loose cell structure and electrode displacement. The broken electrode surface can easily puncture the separator, causing internal short circuits, thermal runaway, and safety accidents. Similarly, stacked cells are prone to cracking at stress concentration points at the cell edges, leading to electrode breakage, battery failure, and safety issues.

[0075] Increasing the strength of the current collector improves the cell's resistance to cycle expansion and delays the time when cracks appear on the outer ring or edge of the cell, leading to electrode breakage. However, increasing the current collector's strength often severely hinders the movement of dislocations in the internal lattice, thus increasing its brittleness and deteriorating its bending resistance. Studies have shown that wound cells using high-strength current collectors are prone to brittle fracture preferentially in the inner ring with high bending degree during cycling, which can also lead to battery failure. How to improve the current collector's strength while maintaining its bending resistance, thereby delaying the time of crack initiation and electrode failure in the cell, and comprehensively improving battery cycle life and safety performance, has become an urgent technical problem to be solved.

[0076] Based on this, such as Figure 1 As shown, the first aspect of this application provides a current collector 6, which includes a surface layer 62 and an intermediate layer 61 disposed between the surface layers 62. The intermediate layer includes a first metal element, and the total mass content of the first metal element is greater than or equal to 80% based on the total mass of the intermediate layer elements. The surface layer includes a second metal element, and the total mass content of the second metal element is greater than or equal to 80% based on the total mass of the surface layer elements. The tensile strength of the intermediate layer is greater than or equal to the tensile strength of the surface layer, and the bending resistance of the surface layer is greater than or equal to the bending resistance of the intermediate layer.

[0077] The layered structure of the current collector can be tested using any method known in the art. For example, the layered structure of the current collector can be characterized by metallographic analysis; alternatively, an energy dispersive spectroscopy (EDS) instrument combined with argon ion polishing and scanning electron microscopy (SEM) can be used to perform a cross-sectional scan of the current collector to obtain an elemental distribution map of the current collector cross-section, showing that the current collector provided in this embodiment exhibits a multi-layered structure in the cross-section. In the elemental distribution map of the current collector cross-section, the layer located on the upper or lower surface of the current collector is the surface layer, and the layer disposed between the surface layers in the thickness direction is the intermediate layer. The elemental types and mass content of each layer can be obtained by performing EDS analysis on the cross-section or surface of each layer of the current collector. It should be noted that the surface layer and the intermediate layer can be identified by a clear compositional boundary in the current collector cross-section, but this does not necessarily mean that there is a clear stratification between them in the cross-sectional morphology.

[0078] Based on the total mass of the intermediate layer elements, the mass content of the first metal element can be obtained by surface scanning of the intermediate layer using an energy dispersive spectrometer. Based on the total mass of the surface layer elements, the mass content of the second metal element can be obtained by surface scanning of the surface layer using an energy dispersive spectrometer.

[0079] In some embodiments, the surface layer and the intermediate layer are disposed adjacent to each other in the thickness direction; in other embodiments, other arbitrary functional layers are disposed between the intermediate layer and the surface layer. It is understood that the relevant characteristics of the surface layer can be obtained by measuring the surface layer region in the cross-section of the current collector, or by directly characterizing the surface of the current collector.

[0080] In some implementations, based on the total mass of the intermediate layer elements, the total mass content of the first element can be selected as 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.98%, 100%, or any value range between the two.

[0081] In some embodiments, based on the total mass of the surface layer elements, the total mass content of the second metal element can be selected as 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.5%, 99.6%, 99.7%, 99.8%, 99.98%, 100%, or any value range between the two.

[0082] In this paper, the term "tensile strength" refers to the maximum load-bearing capacity of a specimen when it is subjected to continuous loading until it breaks.

[0083] In this paper, the term "bending resistance" refers to the ability of a specimen to withstand bending, which can be characterized by the number of times the specimen can be bent.

[0084] The tensile strength of the intermediate layer and the surface layer can be tested using any method known in the art. As an example, the intermediate layer is obtained by etching the surface layer elements of the current collector using any known method. The tensile strength of the obtained intermediate layer and the current collector is then tested under the same test conditions. According to the principles of composite material mechanics, if the tensile strength of the intermediate layer is greater than or equal to the tensile strength of the current collector, it indicates that the tensile strength of the intermediate layer is greater than or equal to the tensile strength of the surface layer.

[0085] In this application, the tensile strength of the interlayer and current collector can be tested using methods known in the art, such as referring to GB / T 5230-1995 "Electrolytic Copper Foil" standard. As an example, at least 10 specimens with a length of 200±0.5 mm, a width of 15±0.25 mm, and a thickness of 6±0.2 μm are cut. The specimens are continuously loaded at a tensile speed of 50±0.5 mm / min at room temperature until fracture. The tensile strength of the specimen is obtained by dividing the maximum load by the cross-sectional area of ​​the specimen. The cross-sectional area of ​​the specimen can be measured by dimensional measurement.

[0086] The bending resistance of the intermediate layer and the surface layer can be tested using any method known in the art. As an example, the intermediate layer is obtained by etching the surface layer elements of the current collector using any known method. The intermediate layer and the current collector are then subjected to a bending resistance test under the same test conditions. According to the principles of composite material mechanics, if the bending resistance of the current collector is greater than or equal to that of the intermediate layer, it indicates that the bending resistance of the surface layer is greater than or equal to that of the intermediate layer.

[0087] In this application, the number of times the intermediate layer and the current collector can be bent can be tested using methods known in the art, such as folding the sample 180° and then rolling it back and forth at the fold with a 1.5kg roller, unfolding it and observing whether cracking and light transmission occur at the fold. Record the number of times the folding point cracks and light transmission occurs, test at least ten samples, and take the average value.

[0088] This current collector achieves a balance between strength and bending resistance through a multi-layer design. The middle layer has relatively high tensile strength, while the surface layer has relatively high bending resistance. This improves the bending resistance of the current collector while maintaining its high strength, delaying the time for the electrode to crack during the cycle of the secondary battery, thus increasing the cycle life of the secondary battery and reducing safety risks.

[0089] In some embodiments, the first metallic element includes one or more of Fe, Sn, Ni, and Zn.

[0090] Metal materials with the aforementioned first metallic element as the main component often have high strength, which is beneficial for improving the tensile strength of the current collector, delaying the time when cracks appear on the outer ring of the electrode during cycling, and thus improving the cycle life of the battery.

[0091] In some embodiments, the second metallic element includes Cu.

[0092] Copper metal materials often have high ductility, which helps improve the bending resistance of the current collector and delays the time when cracks appear in the inner ring of the electrode during cycling, thus improving the cycle life of the battery.

[0093] In some embodiments, the average grain size of the surface layer is greater than or equal to 1.7 μm.

[0094] The average grain size of the surface layer can be tested using methods known in the art. For example, the inverse pole figure distribution can be obtained by measuring the surface layer (e.g., a copper layer) of the current collector using a combination of cross-sectional electron backscatter diffraction (EBSD) and scanning electron microscopy. Figure 2 As shown. The grain size in the inverse pole figure of the current collector surface layer is plotted, and a quantity distribution diagram is created. A statistical distribution curve is then fitted, and the length corresponding to the peak value is taken as the average grain size. The grain size is represented by the equivalent circle diameter of the grain.

[0095] In some embodiments, the average grain size of the surface layer can be selected as 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or any value range between the two.

[0096] Surface layers with an average grain size within the above range can improve the bending resistance of the current collector and delay the time when cracks appear in the inner ring of the cell during cycling.

[0097] In some embodiments, the average grain size of the surface layer is 1.7 μm-3.5 μm, and can be selected as 1.9 μm-2.5 μm.

[0098] Surface layers with an average grain size within the above range can better balance the strength and bending resistance of the current collector, delay the time when the cell cracks during cycling, improve the cycle life of the secondary battery, and reduce safety risks.

[0099] In some embodiments, the diffraction intensity of the (111) crystal plane in the surface layer accounts for 20%-40% of the total diffraction intensity of the (111), (200), (220), (311), and (222) crystal planes in the surface layer.

[0100] In this application, the diffraction intensity of the crystal planes in the surface layer can be tested using methods known in the art. As an example, an X-ray diffractometer is used to test the surface layer, with reference to standard copper powder (PDF No. 04). The X-ray spectrum of 0836, such as Figure 3 As shown, the diffraction intensity of the (111) crystal plane is taken as the peak area of ​​the diffraction peak located at 40º-45º, the diffraction intensity of the (200) crystal plane is taken as the peak area of ​​the diffraction peak located at 47º-52º, the diffraction intensity of the (220) crystal plane is taken as the peak area of ​​the diffraction peak located at 70º-75º, the diffraction intensity of the (311) crystal plane is taken as the peak area of ​​the diffraction peak located at 85º-95º, and the diffraction intensity of the (222) crystal plane is taken as the peak area of ​​the diffraction peak located at 93º-100º.

[0101] In some embodiments, the ratio of the diffraction intensity of the (111) crystal plane in the surface layer to the sum of the diffraction intensities of the (111), (200), (220), (311), and (222) crystal planes in the surface layer can be selected as 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, or any value range between the two.

[0102] For crystalline copper, common crystal planes include (111), (200), (220), (311), and (222). According to crystallographic properties, the (111) crystal plane has a high atomic density and high mechanical strength, which can improve the strengthening effect. The intensity ratio of the diffraction peaks of a crystal plane can be used to characterize the orientation probability of that crystal plane, also known as preferred orientation or preferred orientation. In the prior art, the orientation ratio of the (111) crystal plane in the copper foil of the high-performance current collector is about 45%~55%. In the embodiments of this application, the diffraction intensity ratio of the (111) crystal plane is controlled to 20%-40% to improve the bending resistance of the current collector, so as to achieve a balance between the strength and bending resistance of the current collector, improve the cycle life of the secondary battery, and reduce safety risks.

[0103] In some embodiments, the diffraction intensity of the (111) crystal plane in the surface layer accounts for 25% to 35% of the total diffraction intensity of the (111), (200), (220), (311), and (222) crystal planes in the surface layer.

[0104] The diffraction intensity ratio of the (111) crystal plane in the surface layer within the above range can further balance the strength and bending resistance of the current collector, comprehensively improve the cycle life of the secondary battery, and reduce safety risks.

[0105] In some embodiments, the average grain size of the intermediate layer is 0.1 μm-1 μm.

[0106] The average grain size of the intermediate layer can be tested using any method known in the art. As an example, the cross-section of the current collector is measured using a cross-sectional electron backscatter diffractometer (EBSD) and a scanning electron microscope to obtain an inverse pole figure distribution. The grain size of the intermediate layer portion in the cross-section is statistically analyzed, and a quantity distribution map is plotted. A statistical distribution is then fitted, and the length corresponding to the peak value is taken as the average grain size. The diameter of the equivalent circle of the grain is used as the grain size.

[0107] In some embodiments, the average grain size of the intermediate layer can be selected as 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm or any value range between the two.

[0108] Current collectors with an average grain size in the intermediate layer within the above range have higher strength, which can reduce the probability of cracks appearing on the outer ring of wound cells and on the edges of laminated cells.

[0109] In some embodiments, the thickness of the current collector is 3μm-8μm.

[0110] In some embodiments, the thickness of the current collector can be selected as 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm or any value range between the two.

[0111] This current collector has a low thickness, which enables effective weight reduction of the battery and is conducive to further improving the battery's energy density.

[0112] In some embodiments, the thickness of the intermediate layer is 2μm to 6μm, and the thickness of the surface layer on one side is 0.5μm to 2μm.

[0113] In this application, the thickness of the intermediate layer and the surface layer on one side can be tested using methods known in the art. As an example, the current collector is longitudinally cut using argon ion polishing technology to test the thickness of each layer.

[0114] In some embodiments, the thickness of the intermediate layer can be selected as 2μm, 3μm, 4μm, 5μm, 6μm or any value range between the two.

[0115] In some embodiments, the thickness of the surface layer on one side may be selected as 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2.0 μm or any value range between the two.

[0116] Current collectors with thicknesses of the intermediate layer and the surface layer within the above-mentioned range can effectively balance the strength and bending resistance of the current collector, improve the cycle life of the secondary battery, and enhance the safety of the secondary battery.

[0117] In some embodiments, under test conditions of room temperature, sample thickness of 6±0.2μm, and tensile speed of 50±0.5mm / min, the tensile strength of the current collector is greater than or equal to 900MPa.

[0118] In this article, the term "room temperature" refers to 20±10℃.

[0119] In some embodiments, under test conditions of room temperature, sample thickness of 6 μm ± 0.2 μm, and tensile speed of 50 ± 0.5 mm / min, the tensile strength of the current collector can be selected as 900 MPa, 950 MPa, 1000 MPa, 1050 MPa, 1100 MPa, 1150 MPa, 1200 MPa, 1250 MPa, 1300 MPa, 1350 MPa, 1400 MPa, 1450 MPa, 1500 MPa, or any value range between the two.

[0120] The aforementioned current collector has high strength, which can improve the cell's resistance to expansion, increase the battery's cycle life, and improve the battery's safety performance.

[0121] In some embodiments, under test conditions of room temperature, sample thickness of 6±0.2μm, and tensile speed of 50±0.5mm / min, the tensile strength of the current collector is greater than or equal to 1000MPa.

[0122] Current collectors with a tensile strength of 1000 MPa or higher can reduce the risk of premature cracking at the outer ring or edge of the cell under expansion force during battery cycling, thus further improving battery safety.

[0123] In some embodiments, under test conditions of room temperature, sample thickness of 6±0.2μm, and tensile speed of 50±0.5mm / min, the tensile strength of the current collector is 1000MPa-1250MPa.

[0124] Current collectors with tensile strength within the above range can balance strength and bending resistance, thus comprehensively improving the cycle life of the battery.

[0125] In some embodiments, under test conditions of room temperature and a sample thickness of 6±0.2μm, the current collector can be bent more than or equal to 7 times.

[0126] In this application, the test method for the number of bends is to fold the current collector 180°, roll it back and forth at the fold with a 1.5kg roller, unfold it, and observe whether cracking and light transmission occur at the fold. The number of rolls that cause cracking and light transmission at the fold is recorded. The more times the current collector can be bent, the better its bending resistance and the less likely it is to break brittlely.

[0127] In some embodiments, under test conditions of room temperature and a sample thickness of 6±0.2μm, the number of times the current collector can be bent can be selected as 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 times or any value range between the two.

[0128] The aforementioned current collector has good bending resistance, which can reduce the probability of premature cracking at the bending points inside the cell, leading to battery failure and improving the cycle life of the battery.

[0129] In some embodiments, under test conditions of room temperature and a sample thickness of 6±0.2μm, the current collector can be bent 7 to 18 times.

[0130] Current collectors with a bending life within the above range can balance bending resistance and strength, thus comprehensively improving the cycle life of the battery.

[0131] On the other hand, this application provides a method for preparing a current collector, the method specifically including: obtaining an intermediate layer, the intermediate layer comprising a first metal element, wherein the mass content of the first metal element is greater than or equal to 80% based on the total mass of the intermediate layer elements; depositing a surface layer on the surface of the intermediate layer to obtain a current collector; the surface layer comprising a second metal element, wherein the mass content of the second metal element is greater than or equal to 80% based on the total mass of the surface layer elements; the tensile strength of the intermediate layer is greater than or equal to the tensile strength of the surface layer, and the bending resistance of the surface layer is greater than or equal to the bending resistance of the intermediate layer.

[0132] This current collector achieves a balance between strength and bending resistance through a multi-layer design. The middle layer has relatively high tensile strength, while the surface layer has relatively high bending resistance. This improves the bending resistance of the current collector while maintaining its high strength, delaying the time for the electrode to crack during the cycle of the secondary battery, thus increasing the cycle life of the secondary battery and reducing safety risks.

[0133] In some embodiments, the surface layer is deposited on the surface of the intermediate layer by electroplating. The electroplating method specifically includes applying an electric current to an electroplating solution, causing copper ions in the electroplating solution to be reduced and deposited to form a surface layer on the surface of the intermediate layer.

[0134] In this article, the term "electroplating" refers to a method that uses the principle of electrolysis to deposit metal or alloy onto the surface of a workpiece to form a metal layer.

[0135] In some implementations, the intermediate layer is also prepared by electroplating.

[0136] In some implementations, the current is direct current and / or alternating current.

[0137] In some embodiments, the electroplating solution includes additives, which include one or more of leveling agents, wetting agents, and brighteners.

[0138] In this article, the term "leveling agent" refers to a substance added to the electroplating solution that can improve the smoothness of the plating layer.

[0139] In this article, the term "wetting agent" refers to a substance used to reduce the interfacial tension between the electroplating solution and the electrode, thereby enabling the coating to adhere better to the substrate.

[0140] In this article, the term "brightener" refers to a substance that improves the smoothness of the coating and reduces surface roughness.

[0141] Leveling agents can adhere to the tips of copper foils with fast deposition rates, inhibiting grain growth, balancing the growth rates of pits and tips, and improving the flatness of the copper foil. Wetting agents can improve the wettability of the plating solution and the substrate. The wettability of the plating solution on the cathode is sufficient to enable rapid electrodeposition with high current, increasing the nucleation rate of the copper foil and controlling the average grain size in the copper foil. Brighteners can work in conjunction with leveling agents to regulate the grain size of the copper foil, reduce the surface roughness of the copper foil, and improve the surface smoothness.

[0142] In some embodiments, the additives include leveling agents, wetting agents, and brightening agents.

[0143] The above three additives can be combined to prepare a surface layer that gives the current collector both strength and bending resistance.

[0144] In some embodiments, the leveling agent is present in a concentration of 40 mg / L to 80 mg / L in the electroplating solution.

[0145] In some embodiments, the concentration of the leveling agent in the electroplating solution may be selected as 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L, 65 mg / L, 70 mg / L, 75 mg / L, 80 mg / L, or any value range between the two.

[0146] In some embodiments, the concentration of the wetting agent in the electroplating solution is 30 mg / L-80 mg / L.

[0147] In some embodiments, the concentration of the wetting agent in the electroplating solution may be selected as 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L, 65 mg / L, 70 mg / L, 75 mg / L, 80 mg / L, or any range between the two.

[0148] Wetting agents with concentrations within the above range in the electroplating solution are beneficial for depositing copper grains of appropriate size on the surface layer, balancing the strength and bending resistance of the current collector, and improving the cycle life of the secondary battery.

[0149] In some embodiments, the concentration of chloride ions in the electroplating solution is 30 mg / L-60 mg / L.

[0150] In some embodiments, the concentration of chloride ions in the electroplating solution can be selected as 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L, or any range between the two.

[0151] In some embodiments, the concentration of copper ions in the electroplating solution is 50 g / L to 100 g / L.

[0152] In some embodiments, the concentration of copper ions in the electroplating solution can be selected as 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L, or any value range between the two.

[0153] In some embodiments, the concentration of the brightener in the electroplating solution is 10 mg / L-25 mg / L.

[0154] In some embodiments, the concentration of the brightener in the electroplating solution may be selected as 10 mg / L, 11 mg / L, 12 mg / L, 13 mg / L, 14 mg / L, 15 mg / L, 16 mg / L, 17 mg / L, 18 mg / L, 19 mg / L, 20 mg / L, 21 mg / L, 22 mg / L, 23 mg / L, 24 mg / L, 25 mg / L, or any range between the two.

[0155] In some embodiments, the total mass concentration of the leveling agent and the brightening agent in the electroplating solution is less than 100 mg / L.

[0156] In some embodiments, the total mass concentration of the leveling agent and the brightening agent in the electroplating solution can be selected as 70 mg / L, 75 mg / L, 80 mg / L, 85 mg / L, 88 mg / L, 90 mg / L, 95 mg / L, or any value range between the two.

[0157] Leveling agents and brighteners with concentrations within the above range in the electroplating solution are beneficial for depositing copper grains of appropriate size on the surface layer, taking into account both the strength and bending resistance of the current collector, and improving the cycle life of the secondary battery.

[0158] In some embodiments, the electroplating temperature is 50±5°C.

[0159] In some embodiments, the electroplating temperature can be selected as 45°C, 46°C, 47°C, 48°C, 49°C, 50°C, 51°C, 52°C, 53°C, 54°C, 55°C or any range between the two.

[0160] In some embodiments, the pH of the electroplating solution is 4-7.

[0161] In some embodiments, the pH of the electroplating solution can be selected as 4, 5, 6, 7 or any range between two of them.

[0162] In some embodiments, the leveling agent includes one or more of gelatin and Janus Green; the wetting agent includes one or more of hydroxyethyl cellulose and polyethylene glycol; and the brightening agent includes one or more of sodium dithiodipropane sulfonate, sodium 3-mercapto-1-propane sulfonate, and thiourea.

[0163] In some embodiments, the electroplating solution includes gelatin at a concentration of 40 mg / L-80 mg / L, hydroxyethyl cellulose at a concentration of 30 mg / L-80 mg / L, sodium polydisulfide dipropane sulfonate at a concentration of 10 mg / L-25 mg / L, copper ions at a concentration of 50 g / L-100 g / L, and chloride ions at a concentration of 30 mg / L-60 mg / L.

[0164] In some embodiments, the electroplating solution includes gelatin with a concentration of 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L, 65 mg / L, 70 mg / L, 75 mg / L, 80 mg / L, or any value range thereof; hydroxyethyl cellulose with a concentration of 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L, 65 mg / L, 70 mg / L, 75 mg / L, 80 mg / L, or any value range thereof; and hydroxyethyl cellulose with a concentration of 10 mg / L, 15 mg / L, 20 mg / L, or any value range thereof. Sodium polydisulfide dipropane sulfonate with concentrations of 25 mg / L or any range thereof; copper ions with concentrations of 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L, 90 g / L, 95 g / L, 100 g / L or any range thereof; and chloride ions with concentrations of 30 mg / L, 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L or any range thereof.

[0165] In some embodiments, the current density of the direct current is 4000 A / m. 2 -8000A / m 2 The electroplating time is 0.5 min to 3 min.

[0166] In some embodiments, the current density of the direct current can be selected as 4000 A / m. 2 4500 A / m 2 5000 A / m 2 5500 A / m 2 6000A / m 2 6100A / m 2 6200A / m 2 6300A / m 2 6400A / m 2 6500A / m 2 6600A / m 2 6700A / m 2 6800A / m 2 6900A / m 2 7000A / m 2 7500 A / m 2 8000 A / m 2 Or the range of values ​​between any two.

[0167] In some embodiments, the electroplating time can be selected as 0.5 min, 1 min, 1.5 min, 2 min, 2.5 min, 3 min, or any value range between the two.

[0168] In some embodiments, the preparation method further includes: heat-treating the current collector to obtain an annealed current collector.

[0169] In some embodiments, the heat treatment temperature is 60°C to 80°C.

[0170] In some embodiments, the temperature of the heat treatment can be selected as 60°C, 65°C, 70°C, 75°C, 80°C or any value range between the two.

[0171] In some embodiments, the heat treatment time is 12h to 25h.

[0172] In some embodiments, the heat treatment time can be selected as 12h, 13h, 14h, 15h, 17h, 20h, 23h, 25h or any range between the two.

[0173] After annealing, the grain size in the current collector increases further, and the intensity ratio of the diffraction peak of the (111) crystal plane decreases further, which is conducive to further improving the bending resistance of the current collector, achieving a balance between the strength and bending resistance of the current collector, and comprehensively improving the cycle life of the secondary battery.

[0174] In some embodiments, the preparation method is a continuous production method.

[0175] On the other hand, this application provides a composite foil, which includes any feature of the current collector of any embodiment of this application or any feature of the current collector prepared by the preparation method of any embodiment of this application.

[0176] In some embodiments, the maximum width of the composite foil is greater than or equal to 1.5 meters, and / or the maximum length of the composite foil is greater than or equal to 10,000 meters.

[0177] In some embodiments, the maximum width of the composite foil is 1.5 meters, 2 meters, 2.5 meters, 3 meters, 3.5 meters, 4 meters, 6 meters, 8 meters, 10 meters, or any value between two of these.

[0178] In some embodiments, the maximum length of the composite foil is 10,000 meters, 15,000 meters, 20,000 meters, 25,000 meters, 30,000 meters, 60,000 meters, 100,000 meters, or any value between two of these.

[0179] The composite foil provided in this application embodiment can be manufactured in large sizes and has the prospect of industrial application.

[0180] On the other hand, this application provides a secondary battery, which includes an electrode, and the electrode includes the current collector provided in the first aspect of this application.

[0181] In some implementations, the electrode is a positive electrode.

[0182] In some implementations, the electrode is a negative electrode.

[0183] In some embodiments, the negative electrode includes a current collector and a negative electrode film layer disposed on at least one surface of the current collector.

[0184] In some embodiments, the negative electrode film layer comprises a negative electrode active material. In some embodiments, the negative electrode active material 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. The silicon-based material may include one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy materials. The tin-based material may include one or more of elemental tin, tin oxide, and tin alloy materials.

[0185] 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.

[0186] 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).

[0187] 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.

[0188] 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.

[0189] 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.

[0190] On the other hand, this application also provides an electrical device including a secondary battery according to any embodiment of this application, wherein the secondary battery may be in the form of a battery cell, a battery module or a battery pack.

[0191] This application does not impose any particular limitation on the type of secondary battery; for example, the secondary battery can be a lithium-ion battery. Typically, a secondary battery includes a positive electrode, a negative electrode, and an electrolyte. During the charging and discharging process of the secondary battery, active ions repeatedly insert and extract between the positive and negative electrodes, and the electrolyte acts as a conductor for these active ions. This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). Secondary batteries using electrolyte solutions, and some secondary batteries using solid electrolytes, may also include a separator membrane disposed between the positive and negative electrodes to provide isolation.

[0192] [Positive electrode plate] In some embodiments, 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. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0193] The positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0194] The positive electrode film layer generally includes a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is generally formed by coating a positive electrode slurry on the positive electrode current collector and then drying and cold pressing. The positive electrode slurry is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto. As an example, the binder for the positive electrode film layer may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin. As an example, the conductive agent for the positive electrode film layer includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0195] The positive electrode active material can be a positive electrode active material for secondary batteries known in the art.

[0196] When the secondary battery of the present application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of the lithium-containing phosphates may include, but are not limited to, lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds.

[0197] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery may include a lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and its modified compounds. 0.8 ≤ a ≤ 1.2, 0.5 ≤ b < 1, 0 < c < 1, 0 < d < 1, 1 ≤ e ≤ 2, 0 ≤ f ≤ 1, M is selected from one or more of Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti, and B, and A is selected from one or more of N, F, S, and Cl.

[0198] In some embodiments, as an example, the positive electrode active material for lithium-ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0199] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0200] [Electrolytes] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0201] The type of electrolyte salt is not specifically limited and can be selected according to actual needs.

[0202] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0203] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ethylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0204] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics of the secondary battery, such as additives that improve the overcharge performance of the secondary battery, additives that improve the high-temperature performance of the secondary battery, and additives that improve the low-temperature power performance of the secondary battery.

[0205] [Isolation membrane] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0206] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0207] In some embodiments, the positive electrode, the separator, and the negative electrode can be fabricated into an electrode assembly using a winding process or a stacking process.

[0208] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0209] In some embodiments, the outer packaging may be a hard shell, such as a hard plastic shell, aluminum shell, steel shell, etc. The outer packaging may also be a flexible package, such as a pouch. The material of the flexible package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0210] 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. Figure 4 This is an example of a square-structured secondary battery 5.

[0211] In some embodiments, such as Figure 5 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover 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 in 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 adjusted according to requirements.

[0212] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding or stacking process. The electrode assembly is then placed in an outer packaging, dried, and injected with an electrolyte. After vacuum sealing, settling, formation, and shaping, a secondary battery is obtained.

[0213] In some embodiments of this application, the secondary battery according to this application can be assembled into a battery module. The number of secondary batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0214] Figure 6 This is a schematic diagram of battery module 4 as an example. Figure 6 As shown, 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.

[0215] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0216] 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 adjusted according to the application and capacity of the battery pack.

[0217] Figure 7 and Figure 8 This is a schematic diagram of battery pack 1 as an example. Figure 7 and Figure 8As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0218] Electrical appliances This application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack described 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 be, but is not limited to, mobile devices (e.g., mobile phones, tablets, 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.

[0219] The electrical device can be equipped with a secondary battery, battery module, or battery pack according to its usage requirements.

[0220] Figure 9 This is a schematic diagram of an example electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0221] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0222] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0223] Example 1 (1) Preparation of composite foil First, prepare a ferric sulfate solution with a concentration of 20 g / L and a pH value controlled at 6-7. Pour the solution into a Hall effect tank to complete the solution preparation. Then, add the leveling agent gelatin, the brightening agent sodium polydisulfide dipropane sulfonate (SPS), and the wetting agent hydroxyethyl cellulose to the solution, where the gelatin concentration is 70 mg / L, the brightening agent concentration is 25 mg / L, and the wetting agent concentration is 50 mg / L. Heat the solution to 50℃-55℃ and control the current density at 5000 A / m. 2 The process takes about 3 minutes to electroplate an Fe foil with a thickness of 4 μm and an average grain size of 0.2 μm.

[0224] Using Fe foil as the intermediate layer, the generated Fe foil is placed in a solution containing copper sulfate, with the pH controlled at 3-5, connecting the intermediate layer to the negative electrode current. The concentrations are: copper sulfate 80 g / L, sodium chloride 37 mg / L, gelatin (leveling agent) 70 mg / L, sodium polydipropane sulfonate (SPS) (brightening agent) 25 mg / L, and hydroxyethyl cellulose (HEC) (wetting agent) 50 mg / L. The solution is heated to 50-55°C, and the current density is controlled at 6000 A / m. 2 The electroplating process takes about 2 to 3 minutes to generate copper foil with a thickness of 1 μm on both the upper and lower surfaces of the Fe foil, forming a Cu / Fe / Cu composite foil with a thickness of 6 μm. In addition to unavoidable impurity elements, the main constituent element in the surface layer is Cu; in addition to unavoidable impurity elements, the main constituent element in the middle layer is Fe.

[0225] (2) Battery preparation Preparation of positive electrode sheet Lithium iron phosphate, conductive carbon black, and PVDF were mixed in a mass ratio of 8:1:1, and then N-methylpyrrolidone was added as a solvent. The mixture was coated on both sides of an aluminum foil, and after cold pressing and cutting, a positive electrode sheet was obtained. The positive electrode sheet was rolled into a film roll, and a ceramic slurry was sprayed onto the cut surface of the film roll. In the ceramic slurry, the ceramic material was boehmite, accounting for 39 wt%; the binder was polyacrylate, accounting for 5 wt%; the solvent was N-methylpyrrolidone; the solid content of the slurry was 10%; and the viscosity of the slurry was 800 mPa·s.

[0226] Preparation of negative electrode sheet Artificial graphite, conductive carbon black, binder carboxymethyl cellulose (CMC), and solvent water are uniformly mixed in a weight ratio of 1.1% SBR + 0.9% CMC + 0.7% SP + 97.3% graphite, and coated on both sides of the composite foil prepared above. After cold pressing and cutting, the negative electrode sheet is obtained.

[0227] Preparation of diaphragm A polyethylene film with a thickness of 13 μm was used as the separator.

[0228] Preparation of electrolyte Ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a volume ratio of 1:1:1. LiPF6 was then dissolved in this solution to obtain an electrolyte. The concentration of LiPF6 in this electrolyte was 1 mol / L.

[0229] Battery assembly The electrodes are arranged in the order of "separator-negative electrode-separator-positive electrode". One end of the positive electrode, negative electrode, and two separators is fixed to the discharge roller, and the other end is stacked together and fixed to the winding shaft. The winding shaft is rotated by a motor to wind the positive electrode, negative electrode, and two separators to obtain a wound battery.

[0230] Example 2-3 The preparation methods of Examples 2-3 are basically the same as those of Example 1, except that the composition of the plating solution in the surface layer deposition step is changed, as shown in Table 1.

[0231] Example 4 The preparation method of Example 4 is basically the same as that of Example 1, except that the current collector prepared in Example 1 was subjected to heat treatment at a temperature of 80°C for 12 hours.

[0232] Comparative Example 1 The preparation method of Comparative Example 1 is basically the same as that of Example 1, except that the composition of the plating solution in the surface layer deposition step is adjusted, as shown in Table 1.

[0233] Comparative Example 2 The preparation method of Comparative Example 2 is basically the same as that of Example 1, except that iron foil is used for the negative electrode current collector and the thickness of the iron foil is 6 micrometers.

[0234] Comparative Example 3 The preparation method of Comparative Example 3 is basically the same as that of Example 1, except that the negative electrode current collector uses conventional high-strength copper foil with a thickness of 6 micrometers.

[0235] Table 1

[0236] Test methods (1) The state of charge (SOH) corresponding to a crack in the battery cell At 25℃, the battery is charged at a constant current of 1C until the voltage reaches 3.8V, then charged at a constant voltage of 3.8V until the current ≤0.05C, and finally discharged at a constant current of 1C until the voltage reaches 2.5V. This constitutes one charge-discharge cycle. This cycle is repeated, and then computed tomography (CT) is used to determine whether cracks have formed inside the battery. The remaining state of charge (SOH) at the time cracks appear is recorded. A fresh battery cell has 100% SOH. As active ions are lost during battery cycling, the remaining state of charge of the cell continuously decreases. A larger SOH corresponding to the appearance of cracks in the cell indicates that the cell is prone to cracking in the early stages of cycling, resulting in a lower battery cycle life. Conversely, a smaller SOH corresponding to the appearance of cracks in the cell indicates that cracks appear in the later stages of cycling, resulting in a relatively higher battery cycle life.

[0237] Test Results The test results are shown in Table 2.

[0238] Table 2

[0239] In Comparative Example 3, the existing high-strength copper foil, due to its low tensile strength, preferentially cracks at the outer ring of the cell where the expansion force is greatest during battery cycling. In Comparative Example 2, although the iron foil has high tensile strength, its poor bending resistance leads to preferential cracking at the inner ring of the cell where bending deformation is greatest during battery cycling. The comparison between the examples and the comparative examples shows that a current collector with a copper foil surface layer and an average grain size greater than or equal to 1.7 μm, and an iron foil middle layer, can withstand more cycles of expansion. The state of equilibrium (SOH) corresponding to cell cracking is less than or equal to 60%, which helps improve the cycle life and safety performance of the secondary battery, ensuring that the battery electrodes do not break within the expected service life (e.g., during the warranty period), thus meeting market demands for secondary batteries.

[0240] As can be seen from the comparison between the examples and Comparative Example 1, the concentration of wetting agent in the electroplating solution of 30mg / L-80mg / L is beneficial to reduce nucleation, increase the average size of copper grains on the surface layer, and improve the bending resistance of the current collector.

[0241] It should be noted that this application is not limited to the above-described embodiments. The above 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, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A current collector characterized by comprising: The current collector comprises a surface layer and an intermediate layer arranged between the surface layer, the intermediate layer comprises a first metal element, the total mass content of the first metal element is greater than or equal to 80% based on the total mass of the elements in the intermediate layer, the surface layer comprises a second metal element, the total mass content of the second metal element is greater than or equal to 80% based on the total mass of the elements in the surface layer; The tensile strength of the intermediate layer is greater than or equal to the tensile strength of the surface layer, and the bending resistance of the surface layer is greater than or equal to the bending resistance of the intermediate layer; The diffraction intensity ratio of the (111) crystal face in the surface layer to the sum of the diffraction intensities of the (111) crystal face, the (200) crystal face, the (220) crystal face, the (311) crystal face and the (222) crystal face in the surface layer is 20%-40%.

2. The current collector of claim 1, wherein The first metal element comprises one or more of Fe, Sn, Ni and Zn.

3. The current collector according to claim 1 or 2, characterized by The second metal element comprises Cu.

4. The current collector according to any one of claims 1 to 3, characterized in that, The average grain size of the surface layer is greater than or equal to 1.7 μm.

5. The current collector of any one of claims 1 to 4, wherein, The average grain size of the surface layer is 1.7 μm-3.5 μm.

6. The current collector of any one of claims 1 to 5, wherein, The average grain size of the surface layer is 1.9 μm-2.5 μm.

7. The current collector of any one of claims 1 to 6, wherein The diffraction intensity ratio of the (111) crystal face in the surface layer to the sum of the diffraction intensities of the (111) crystal face, the (200) crystal face, the (220) crystal face, the (311) crystal face and the (222) crystal face in the surface layer is 25%-35%.

8. The current collector of any one of claims 1 to 7, wherein, The average grain size of the intermediate layer is 0.1 μm-1 μm.

9. The current collector of any one of claims 1 to 8, wherein, The thickness of the current collector is 3 μm-8 μm.

10. The current collector of any one of claims 1 to 9, wherein, The thickness of the intermediate layer is 2 μm-6 μm, and the thickness of the surface layer on one side is 0.5 μm-2 μm.

11. The current collector of any one of claims 1 to 10, wherein, The tensile strength of the current collector is greater than or equal to 900 MPa under the test conditions of room temperature, a sample thickness of 6±0.2 μm and a tensile speed of 50±0.5 mm / min.

12. The current collector of any one of claims 1 to 10, wherein, The tensile strength of the current collector is greater than or equal to 1000 MPa under the test conditions of room temperature, a sample thickness of 6±0.2 μm and a tensile speed of 50±0.5 mm / min.

13. The current collector of any one of claims 1 to 10, wherein, The tensile strength of the current collector is 1000 MPa-1250 MPa under the test conditions of room temperature, a sample thickness of 6±0.2 μm and a tensile speed of 50±0.5 mm / min.

14. The current collector of any one of claims 1 to 13, wherein, The number of bendable times of the current collector is greater than or equal to 7 times under the test conditions of room temperature and a sample thickness of 6±0.2 μm.

15. The current collector of any one of claims 1 to 13, wherein, The number of bendable times of the current collector is 7 times-18 times under the test conditions of room temperature and a sample thickness of 6±0.2 μm.

16. A secondary battery characterized by comprising: The secondary battery comprises the current collector according to any one of claims 1-15.

17. An electrical device, comprising: The secondary battery comprises the secondary battery according to claim 16.

18. A method of making a current collector, characterized by, The preparation method specifically comprises: An intermediate layer is obtained, the intermediate layer comprises a first metal element, the mass content of the first metal element is greater than or equal to 80% based on the total mass of the elements in the intermediate layer; A surface layer is deposited on the surface of the intermediate layer by an electroplating method, the electroplating method comprises applying an electric current to an electroplating solution to form a surface layer on the surface of the intermediate layer; The electroplating solution comprises an additive, the additive comprises a wetting agent, and a concentration of the wetting agent in the electroplating solution is 30 mg / L-80 mg / L. The surface layer comprises a second metal element, and a mass content of the second metal element is greater than or equal to 80% based on a total mass of elements in the surface layer; a tensile strength of the intermediate layer is greater than or equal to a tensile strength of the surface layer, and a bending resistance of the surface layer is greater than or equal to a bending resistance of the intermediate layer.

19. The method of claim 18, wherein, The electroplating method specifically comprises applying an electric current to the electroplating solution, so that copper ions in the electroplating solution are reduced and deposited to form a surface layer on a surface of the intermediate layer.

20. The method of manufacturing according to claim 18 or 19, wherein, The additive comprises one or more of a leveling agent and a brightener.

21. The method of claim 20, wherein, The additive comprises a leveling agent, a wetting agent and a brightener.

22. The production method according to any one of claims 18 to 21, characterized by, The electroplating solution satisfies one or more of the following conditions: (1) a concentration of the leveling agent in the electroplating solution is 40 mg / L-80 mg / L; (2) a concentration of chloride ions in the electroplating solution is 30 mg / L-60 mg / L; (3) a concentration of copper ions in the electroplating solution is 50 g / L-100 g / L; (4) a concentration of the brightener in the electroplating solution is 10 mg / L-25 mg / L; (5) a total mass concentration of the leveling agent and the brightener in the electroplating solution is less than 100 mg / L; (6) a temperature of the electroplating is 50±5 ℃; (7) a pH of the electroplating solution is 4-7.

23. The production method according to any one of claims 20 to 22, characterized by, The leveling agent comprises one or more of gelatin and gentian violet; the wetting agent comprises one or more of hydroxyethyl cellulose and polyethylene glycol; and the brightener comprises one or more of sodium poly(dithiopropyl sulfone), sodium 3-mercapto-1-propane sulfonate and thiourea.

24. The production method according to any one of claims 18 to 23, characterized by, The electroplating solution comprises gelatin with a concentration of 40 mg / L-80 mg / L, hydroxyethyl cellulose with a concentration of 30 mg / L-80 mg / L, poly(dithiopropyl sulfone) with a concentration of 10 mg / L-25 mg / L, copper ions with a concentration of 50 g / L-100 g / L, and chloride ions with a concentration of 30 mg / L-60 mg / L.

25. The production method according to any one of claims 18 to 24, characterized by, The current density of the direct current is 4000 A / m 2 - 8000 A / m 2 The time of the electroplating method is 0.5-3 minutes.

26. The production method according to any one of claims 18 to 25, characterized by, The preparation method further comprises: heat treating the current collector to obtain an annealed current collector.

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