Electrolytic copper foil, method for producing the same, negative electrode sheet, and secondary battery

Abstract

The application relates to an electrolytic copper foil and a preparation method thereof, a negative pole piece and a secondary battery. The electrolytic copper foil comprises at least one copper layer, a proportion coefficient of columnar crystals and equiaxed crystals in a section along a thickness direction of the copper layer is T JM , a maximum value of a grain boundary angle average is KAM max , and a grain size is R, wherein the section satisfies at least one of the following conditions (1)-(3): (1) 0.2<=T JM <=0.4; (2) KAM max <=5.5 DEG; and (3) a proportion of grains with R<=0.3 mu m is 40%-50%, a proportion of grains with R<=0.4 mu m is 70%-80%, and a proportion of grains with R<=0.5 mu m is greater than or equal to 95%. The electrolytic copper foil has high tensile strength, high elongation and high thermal stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to an electrolytic copper foil, a preparation method thereof, a negative electrode sheet and a secondary battery. BACKGROUND

[0002] With the rapid development of new energy technology, the demand for high-performance secondary batteries is increasing. The performance improvement of lithium-ion batteries, as the core of new energy storage technology, cannot be achieved without high-quality electrode materials. Copper foil is commonly used as the negative electrode current collector of secondary batteries, which has an important influence on the overall performance and safety of the battery. The copper foils currently used mainly include calendered copper foils based on a calendering process and electrolytic copper foils based on an electroplating process. The production technology of calendered copper foils has high requirements, complex process and high cost, and is not suitable for large-scale production, so people gradually shift their focus to electrolytic copper foils. However, in order to meet the current high-quality energy density requirements of secondary batteries, electrolytic copper foils not only need to be thinner, but also need to have sufficient tensile elongation performance and thermal stability. The mechanical properties of existing electrolytic copper foils cannot meet the requirements of high-quality energy density secondary batteries, and wrinkles, broken strips and other problems often occur during the cold pressing process of the negative electrode sheet or during the winding or lamination of the battery and the battery cycle, which greatly affects the production efficiency and service life of the secondary battery. SUMMARY

[0003] The present application provides an electrolytic copper foil, a preparation method thereof, a negative electrode sheet and a secondary battery, which aims to make the electrolytic copper foil have high tensile strength and high elongation rate, and have high thermal stability.

[0004] To achieve the above-mentioned purpose, the first aspect of the present application provides an electrolytic copper foil, comprising at least one copper layer, the proportion coefficient of columnar crystals to equiaxed crystals in the cross section of the copper layer along the thickness direction is T JM , T JM =N (I＞1) / N (I≤1) , wherein N is the number of grains, I is the grain aspect ratio calculated by fitting an ellipse in the EBSD grain size measurement data, the maximum value of the average grain boundary angle in the cross section is KAM max , wherein, is the grain boundary angle of each grain boundary, n is the total number of grain boundaries, and the grain size in the cross section is R, wherein the cross section satisfies at least one of the following conditions (1) to (3):

[0005] (1) 0.2≤T JM ≤0.4;

[0006] (2) KAM max ≤5.5°;

[0007] (3) The proportion of crystal grains with R≤0.3 μm is 40%-50%, the proportion of crystal grains with R≤0.4 μm is 70%-80%, and the proportion of crystal grains with R≤0.5 μm is greater than or equal to 95%.

[0008] Therefore, the electrolytic copper foil provided by the application has high tensile strength and high elongation, and has high thermal stability, which can effectively reduce the possibility of striping and / or wrinkling in the manufacturing process of the electrolytic copper foil and / or in the manufacturing and use process of the secondary battery.

[0009] In any embodiment of the application, the copper layer has two surfaces opposite in the thickness direction of the copper layer, namely a first surface and a second surface, and the first surface and the second surface have different surface roughness and / or brightness.

[0010] In any embodiment of the application, the electrolytic copper foil further comprises at least one protective layer, which optionally comprises a first protective layer and a second protective layer, the first protective layer is arranged on the first surface, and the second protective layer is arranged on the second surface.

[0011] In any embodiment of the application, the protective layer comprises at least one of chromium, glucose and nitride;

[0012] Optionally, the protective layer comprises chromium, and further optionally, the content of the chromium in at least one of the protective layers is 20 ppm-80 ppm.

[0013] In any embodiment of the application, the thickness of the first protective layer is 100 nm-300 nm, and / or the thickness of the second protective layer is 100 nm-300 nm.

[0014] In any embodiment of the application, the thickness of the copper layer is 4 μm-8 μm.

[0015] In any embodiment of the application, the tensile strength of the electrolytic copper foil at room temperature is 60 kgf / mm 2 -70 kgf / mm 2 , and / or the elongation of the electrolytic copper foil at room temperature is ≥4.5%, and the room temperature is 10°C-40°C.

[0016] In any embodiment of the application, the attenuation rate Rmi of the tensile strength of the electrolytic copper foil is ≤3.5%, Rmi=(R m1 -R m2 ) / R m1 *100%, wherein R m1 and R m2The tensile strength of the electrolytic copper foil at room temperature and the tensile strength of the electrolytic copper foil after heat treatment, respectively, the room temperature is 10-40℃, and the heat treatment temperature is 100-250℃.

[0017] The second aspect of the present application provides a method for preparing an electrolytic copper foil, comprising the following steps:

[0018] The anode and the cathode to be plated are placed in an electrolyte to obtain an electrolytic copper foil, wherein the electrolyte comprises copper ions, sulfuric acid, chloride ions, a leveling agent, a brightener, and a wetting agent.

[0019] Optionally, the concentration of the copper ions in the electrolyte is 70-100 g / L.

[0020] Optionally, the concentration of the sulfuric acid in the electrolyte is 80-140 g / L.

[0021] Optionally, the mass concentration of the chloride ions in the electrolyte is 10-25 ppm.

[0022] Optionally, the mass concentration of the leveling agent in the electrolyte is 1-15 ppm.

[0023] Optionally, the mass concentration of the brightener in the electrolyte is 10-60 ppm.

[0024] Optionally, the mass concentration of the wetting agent in the electrolyte is 5-20 ppm.

[0025] In any embodiment of the present application, the leveling agent is a nitrogen-containing compound, which optionally comprises one or more of gelatin, collagen, gentian violet, and tetrahydrothiazolthione and polyethylene imine compounds; and / or,

[0026] The brightener is an organic divalent sulfide, which optionally comprises one or more of 3-mercapto-1-propane sulfonic acid sodium, polydithiodipropyl sulfone sodium, bis-(sulfonethyl sulfonic acid sodium)-disulfide, and 1,3-propanedisulfonic acid; and / or,

[0027] The wetting agent is a polyether compound, which optionally comprises one or more of polyethylene glycol, carboxyethyl cellulose, and polyvinyl pyrrolidone.

[0028] In any embodiment of the present application, the temperature of the electrolyte during the electrolysis process is 50-60℃.

[0029] In any embodiment of the present application, the method further comprises the step of placing the electrolytic copper foil in a passivation solution for passivation,

[0030] Optionally, the passivation solution comprises one or more of a chromium source, glucose, and a nitride.

[0031] The third aspect of the present application provides a negative electrode tab, comprising the electrolytic copper foil or the electrolytic copper foil prepared by the method.

[0032] The fourth aspect of the present application provides a secondary battery, comprising the negative electrode tab.

[0033] The fifth aspect of the present application provides an electrical device, comprising at least one of the secondary batteries.

[0034] The electrical device of the present application comprises the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery.

[0035] The details of one or more embodiments of the present application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the application will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0036] For better describing and illustrating the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used for describing the drawings should not be considered as limiting the scope of any one of the disclosed applications, the presently described embodiments or examples, and the best mode of these applications presently understood. Moreover, the same reference numbers are used to represent the same components throughout the drawings. In the drawings:

[0037] Figure 1 EBSD photograph of the cross section of the electrolytic copper foil of Example 1 along the thickness direction;

[0038] Figure 2 EBSD photograph of the cross section of the electrolytic copper foil of Example 2 along the thickness direction;

[0039] Figure 3 EBSD photograph of the cross section of the electrolytic copper foil of Example 3 along the thickness direction. DETAILED DESCRIPTION

[0040] Hereinafter, some embodiments of the electrolytic copper foil and the method for preparing the same, the negative electrode tab, the secondary battery, and the electrical device of the present application are described in detail with appropriate reference to the drawings. However, there can be cases where unnecessary detailed descriptions are omitted. For example, there can be cases where detailed descriptions of matters 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. In addition, 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.

[0041] "ranges" disclosed herein can be defined, for example, by the lower and upper values. Any lower limit can independently be combined with any upper limit to define a range of any value. For example, if a range of 60-120 and 80-110 is listed as exemplary, it is understood that a range of 60-110 and 80-120 are also contemplated. Furthermore, if a minimum range value of 1 and 2 is listed, and if a maximum range value of 3, 4, and 5 is also listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, the use of "or" means "and / or" unless specifically stated otherwise, e.g., "x employs A or B" means "x employs A or B or both." Unless otherwise noted, the use of the term "comprising" means "including but not limited to" and the use of the term "comprises" is interpreted as meaning "including but not limited to." It will be further noted that the

[0042] As used herein the specification "a", "an" or "the" can mean one or more than one unless specified otherwise by context e.g. "comprises a" can mean that one or more "a" are present.

[0043] Unless otherwise indicated, all embodiments and optional embodiments can be combined together in any combination.

[0044] Reference herein to "an embodiment" or "one embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment or implementation of the application. The appearances of the phrase "in one embodiment" or "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily all directed to the same embodiments, or alternative embodiments. It is expressly understood that any of the

[0045] Those skilled in the art can understand that the order of writing each step in the method of each embodiment or example does not mean a strict execution order and does not constitute any limitation on the implementation process. The detailed execution order of each step should be determined by its function and possible internal logic. If not specifically stated, all steps of the present application can be performed in sequence or randomly, and preferably in sequence. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method also comprises step (c), which 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.

[0046] In the present application, the open technical features or technical solutions described by the words "containing", "including", "comprising" and the like do not exclude additional members other than the listed members, and can be regarded as providing both a closed feature or solution composed of the listed members and an open feature or solution including additional members in addition to the listed members. For example, A includes a1, a2 and a3, and unless otherwise specified, it can also include other members or can not include additional members, and can be regarded as providing both the feature or solution that "A is composed of a1, a2 and a3" and the feature or solution that "A includes a1, a2 and a3, and also includes other members". In the present application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0047] In the present application, "optionally", "optional" and "optional" mean that it can or can not be present, that is, it can be selected from either of the two parallel solutions "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified, and there is no contradiction or mutual restriction, each "option" is independent.

[0048] As described in the above background, the copper foil with high tensile strength and high elongation can enable the battery to maintain good performance. However, the existing process technology level presents a negative correlation between tensile strength and elongation, and it is difficult to achieve both, and it is difficult to ensure that the elongation is improved while the tensile strength is improved, and at the same time, the copper foil physical property level fluctuates greatly after high-temperature aging, which requires the development of a new electrolytic copper foil to meet the requirements of high tensile strength, high elongation and high thermal stability.

[0049] In order to achieve the above-mentioned purpose, the first aspect of the present application provides an electrolytic copper foil, comprising at least one copper layer. The proportion coefficient of columnar crystals and equiaxed crystals in the cross section of the copper layer along the thickness direction is denoted as T JMKAM max R

[0050] (1) 0.2 ≤ T JM ≤ 0.4;

[0051] (2) KAM max ≤ 5.5°;

[0052] (3) The proportion of grains with R ≤ 0.3 μm is 40% to 50%, the proportion of grains with R ≤ 0.4 μm is 70% to 80%, and the proportion of grains with R ≤ 0.5 μm is greater than or equal to 95%.

[0053] The electrolytic copper foil satisfying at least one of the above conditions (1) to (3) has both high tensile strength and high elongation, and has high thermal stability, and can effectively reduce the possibility of tearing and / or wrinkling during the manufacturing process of the electrolytic copper foil and / or during the manufacturing and use of the secondary battery.

[0054] Columner and equiaxed grains have meanings known in the art and can be determined and measured by methods known in the art. For example, the morphology of a crystal can be described by fitting an ellipse, where the major and minor axes of the ellipse correspond to the maximum and minimum dimensions of the crystal, respectively. The aspect ratio of the fitted ellipse (i.e., the ratio of the major axis to the minor axis) can be used to quantify the morphological characteristics of the crystal. For example, the aspect ratio of a columnar grain is typically greater than 1, while the aspect ratio of an equiaxed grain is close to 1. The aspect ratio of a columnar grain is typically greater than that of an equiaxed grain, and the growth characteristics of a columnar grain result in significant growth in a particular direction, while growth in other directions is limited. The aspect ratio of an equiaxed grain is close to 1, indicating that its growth is uniform in all directions.

[0055] The proportion coefficient T of columnar grains and equiaxed grains in the cross-section of the copper layer in the thickness direction JM = N (I＞1) / N (I≤1) , where N is the number of grains, and I is the grain aspect ratio calculated by fitting an ellipse in the EBSD grain size measurement data. JMThis information can be obtained through measurement methods known in the art, such as ionizing argon gas and then bombarding the sample surface under an electric field, using physical sputtering at a controlled rate through momentum transfer. This allows for fine polishing of the sample surface, resulting in a smooth profile suitable for EBSD testing. Backscattered electrons emitted from the crystalline sample surface diffract with the sample's crystal structure, forming a diffraction pattern (EBSP) that reflects the crystal's orientation information. Using a fast image analysis algorithm, EBSD automatically captures highly detailed crystal orientation maps from large sample areas. By comparing the crystal orientation differences between adjacent EBSPs, EBSD can identify grain boundaries. If the crystal orientation difference between two regions exceeds a certain threshold (usually a few degrees), they can be considered different grains. By mapping the crystal orientation of the sample surface, a grain distribution map can be constructed. By analyzing these distribution maps, the length and width dimensions of the grains can be measured, and the corresponding aspect ratio can be output. A cross-section of the copper layer along its thickness direction with a ratio of columnar to equiaxed crystals of 0.2 to 0.4 allows for electrolytic copper foil to possess both high tensile strength and high elongation. As described below, the ratio T of columnar to equiaxed crystals in this cross-section... JM When the density is less than 0.2, electrolytic copper foil generally exhibits predominantly equiaxed grains. These equiaxed grains display an isotropic crystal morphology and possess good plasticity and toughness. The growth of equiaxed grains in copper foil is usually accompanied by… <200> Preferred crystal orientation contributes to improved material ductility. Furthermore, the uniform structure of equiaxed crystals facilitates growth that increases grain boundary density, further enhancing ductility but reducing tensile strength. A crystal structure with a higher proportion of equiaxed crystals exhibits lower density and instability during copper foil heat treatment, leading to significant fluctuations in copper foil properties. During battery manufacturing and use, deformation due to applied stress and heat can cause wrinkling of the copper foil. Additionally, the ratio T of columnar crystals to equiaxed crystals in this cross-section... JM When the value is greater than 0.4, the columnar grains of the copper foil occupy more of the copper foil area, the crystal structure of the copper foil is too dense, the copper foil becomes brittle, and thus causes breakage and tearing during battery manufacturing and use.

[0056] The maximum average grain boundary angle in the cross-section along the thickness direction of the copper layer in, Let n be the grain boundary angle for each grain boundary, and n be the total number of grain boundaries. KAM maxThe grain boundaries can be obtained by measurement methods known in the art, for example by EBSD, which identifies grain boundaries by analyzing the difference in crystal orientation of adjacent regions, if the difference in orientation of two regions exceeds a certain threshold (typically a few degrees), it can be considered that they are separated by a grain boundary by different grains. This difference can be determined by comparing the crystallographic characteristics of the EBSPs; EBSD can measure the grain boundary angle, i.e. the difference in orientation between adjacent grains. From the crystal orientation data obtained by EBSD, the grain boundary angle of the two adjacent grains at the grain boundary can be calculated, usually expressed by Euler angles.

[0057] Maximum value of the average of the grain boundary angles KAM in the cross section of the copper layer along the thickness direction max ≤ 5.5°, the electrolytic copper foil can have both high tensile strength and high elongation. (KAM) is a core point composed of 24 nearest neighbor points, which is used to assign a scalar value to each point representing its local grain boundary angle. KAM can qualitatively reflect the degree of uniformization of plastic deformation, and a higher value indicates a higher degree of plastic deformation or a higher defect density. During the plastic deformation of the material, uniform deformation helps to improve the tensile elongation performance of the material. In the area with higher KAM value, due to the higher degree of plastic deformation, stress is more easily concentrated, increasing the probability of crack nucleation, which will reduce the tensile elongation performance of the material. During the deformation of the material, the area with higher KAM value indicates that the stability of the crystal structure is poor, which will cause the material to be more prone to local plastic deformation or fracture when subjected to tensile force. KAM value is also related to the recrystallization behavior of the material. During the heating process after deformation, the area with higher KAM value may be more prone to static recrystallization. During the static recrystallization process, the newly formed grains may gradually grow, which will cause the grain size distribution of the material to become non-uniform, which will reduce the strength and toughness of the material. Especially in the case of long time preservation at high temperature, secondary recrystallization will occur, forming a small amount of large grain structure, which will further reduce the mechanical properties of the material.

[0058] As described below, the maximum value of the average of the grain boundary angles KAM max In the case where the copper foil has a grain boundary angle average maximum value KAM greater than 5.5°, the stability of the crystal structure of the copper foil is poor, both the tensile strength and the elongation will be poor, the high temperature stability is reduced, causing the copper foil to be broken and / or wrinkled during the manufacturing process of the electrolytic copper foil and / or during the manufacturing and use process of the secondary battery.

[0059] The grain size R of the copper layer along the thickness direction is represented by the equivalent circle diameter, which has the meaning known in the art, and the diameter of the circle with the same area as the grain projection is the equivalent circle diameter, which can be measured by methods known in the art, for example by EBSD technology, single measurement.

[0060] The proportion of grains with a grain size R≤0.3 μm in the cross section of the copper layer along the thickness direction is 40%-50%, the proportion of grains with a grain size R≤0.4 μm is 70%-80%, and the proportion of grains with a grain size R≤0.5 μm is greater than or equal to 95%, so that the electrolytic copper foil can have both high tensile strength and high elongation. The tensile strength of the copper foil increases with the decrease of the grain size. The tensile strength is closely related to the transfer of slip from the plastic deformed grains to the adjacent grains, and whether this transfer can occur mainly depends on whether the stress concentration generated by the dislocation pile-up group near the grain boundary of the already slipped grain can stimulate the dislocation source in the slip system of the adjacent grain to start and coordinate multiple slips. The refinement of the grain size can generate more grain boundaries, and if the structure of the grain boundary does not change, a greater external force needs to be applied to generate dislocation pile-up, thereby strengthening the material. However, too small grain size can increase the number of grain boundaries, which, as an obstacle to dislocation movement, can improve the strength of the material, but too many grain boundaries can increase the brittleness of the material and reduce its plastic deformation ability. Too large grain size can reduce the density of the grain boundaries and reduce the strength of the material. In particular, in the fine-grain strengthening effect, the increase of the grain size can weaken this strengthening mechanism. Too large grain size is also not conducive to the fatigue life of the material, because the cracks inside the grain are more likely to expand.

[0061] As described below, when the proportion of grains with a grain size R≤0.3 μm in the cross section of the copper layer along the thickness direction is less than 40%, and / or the proportion of grains with a grain size R≤0.4 μm is less than 70%, and / or the proportion of grains with a grain size R≤0.5 μm is less than 95%, the overall grain size of the copper foil is large, the crystal structure is unstable, the tensile strength is low, and the tensile strength attenuation after heat treatment is serious. In the manufacturing process of secondary batteries, the electrolytic copper foil can be broken due to the locally applied pressure. When the proportion of grains with a grain size R≤0.3 μm in the cross section of the copper layer along the thickness direction is greater than 50%, and / or the proportion of grains with a grain size R≤0.4 μm is greater than 80%, the overall grain size of the copper foil is small, the electrolytic copper foil is very brittle and has poor plasticity, and is prone to tearing and breaking during the production process of the electrolytic copper foil. In the manufacturing process of the negative electrode of the secondary battery, tearing is prone to occur at the locally bent position.

[0062] The thickness of the copper layer has the meaning known in the art and can be measured by methods known in the art, for example, by using the areal density method to test the thickness of the copper foil. The thickness of the copper foil can be calculated by the following formula: copper foil thickness = copper foil areal density / copper material density. The areal density can be obtained by weighing the mass of a copper foil sample with a certain area (usually 10*10 cm), and the density of the copper foil material is obtained by a standard reference value (8.9 g / cm 3 ).

[0063] In some embodiments, the thickness of the copper layer is 4 μm to 8 μm. Understandably, the thickness of the copper layer can be 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, and any value or range between any two values thereof. The thickness of the copper layer in this range can further improve the capacity of the battery.

[0064] In some embodiments, the copper foil has two surfaces opposite in the thickness direction of the copper foil, i.e., a first surface and a second surface, and the first surface and the second surface have different surface roughness and / or brightness. Understandably, the vertical distance between the first surface and the second surface is the thickness of the copper layer. The elongation of the copper foil can be further improved.

[0065] In some embodiments, the electrolytic copper foil further comprises at least one protective layer. Optionally, the protective layer comprises a first protective layer and a second protective layer, the first protective layer is disposed on the first surface, and the second protective layer is disposed on the second surface. The protective layer can effectively reduce the oxidation of the surface of the electrolytic copper foil.

[0066] In some embodiments, the protective layer comprises at least one of chromium, glucose, and nitride.

[0067] In some embodiments, the protective layer comprises chromium. Further optionally, the content of chromium in the at least one protective layer is 20 ppm to 80 ppm and any value or range between any two values thereof, for example, it can also be 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm.

[0068] In some embodiments, the thickness of the first protective layer is 100 nm to 300 nm, and / or the thickness of the second protective layer is 100 nm to 300 nm. Understandably, the thickness of the first protective layer can be independently selected from 100 nm to 300 nm and any value or range between any two values thereof, for example, it can also be selected from 150 nm, 200 nm, 250 nm; the thickness of the second protective layer can be independently selected from 100 nm to 300 nm and any value or range between any two values thereof, for example, it can also be selected from 150 nm, 200 nm, 250 nm.

[0069] In some embodiments, the tensile strength of the electrolytic copper foil at room temperature is 60 kgf / mm 2 to 70 kgf / mm 2 and any value or range between any two values thereof, for example, it can also be 62 kgf / mm 2 , 64 kgf / mm 2 , 66 kgf / mm 2 , 68 kgf / mm 2 . The room temperature is 10°C to 40°C.

[0070] In some embodiments, the elongation of the electrolytic copper foil at room temperature is ≥ 4.5%. The room temperature is 10-40°C.

[0071] In some embodiments, the attenuation rate of the tensile strength of the electrolytic copper foil Rmi≤ 3.5%, Rmi= (R m1 -R m2 ) / R m1 * 100%, wherein R m1 and R m2 are the tensile strength of the electrolytic copper foil at room temperature and the tensile strength of the electrolytic copper foil after heat treatment, respectively, the room temperature is 10-40°C, and the heat treatment temperature is 100-250°C. In some embodiments, the heat treatment includes heating the electrolytic copper foil to 250°C at a rate of 5°C / min, and then reducing to room temperature (25°C) at a rate of 5°C / min after 2 hours of heat treatment at 250°C. The attenuation rate of the tensile strength of the electrolytic copper foil Rmiin this range can further reduce the risk of tearing and / or wrinkling during the manufacturing process of the electrolytic copper foil and / or during the manufacturing and use of the secondary battery.

[0072] The electrolytic copper foil undergoes high-temperature aging during post-treatment, and also undergoes long-time high-temperature processes during the manufacturing of the battery and the use of the secondary battery. The attenuation of the high-temperature tensile strength of the electrolytic copper foil has a significant impact on these processes. The tensile strength of the copper foil after heat treatment directly affects its performance as a negative current collector of the lithium battery. A decrease in the tensile strength will lead to a decrease in the mechanical stability of the battery during charging and discharging, affecting the cycle life and safety of the battery. During the electrode manufacturing process of the battery, the copper foil needs to be combined with other materials as a current collector. A decrease in the tensile strength will affect the bonding strength of the copper foil with other materials, and thus affect the overall performance of the electrode. During the assembly of the battery, the decrease in the tensile strength of the copper foil also affects the structural stability of the battery. Too fast attenuation of the tensile strength of the copper foil will lead to cracks or breaks during the assembly or use of the battery, affecting the reliability of the battery.

[0073] As described below, the attenuation rate of the tensile strength of the electrolytic copper foil Rmi> 3.5% will lead to a large gap in the consistency of the tensile strength of the electrolytic copper foil during the manufacturing process and / or during the manufacturing and use of the secondary battery, increasing the risk of tearing and breaking, and deteriorating the performance of the electrode, causing safety problems of the secondary battery.

[0074] The second aspect of the present application provides a method for preparing an electrolytic copper foil, comprising the following steps:

[0075] An anode and a cathode to be plated are placed in an electrolyte to obtain an electrolytic copper foil by electrolysis, wherein the electrolyte comprises copper ions, sulfuric acid, chloride ions, a leveling agent, a brightener, and a wetting agent.

[0076] In some embodiments, the concentration of copper ions in the electrolyte is 70 g / L to 100 g / L and any value or range between any two of them, for example, it can also be 75 g / L, 80 g / L, 85 g / L, 90 g / L, 95 g / L. When the concentration of copper ions is in this range, electrolysis can be carried out at high current density, improving the efficiency of electrolysis. When the concentration of copper ions is high, copper sulfate is easy to precipitate, and when the concentration of copper ions is low, the conductivity of the electrolyte is low, and the current density is also reduced, and the efficiency of electrolysis is low.

[0077] In the process of configuring the electrolyte, the source of copper ions can be copper salt, for example, copper sulfate.

[0078] In some embodiments, the concentration of sulfuric acid in the electrolyte is 80 g / L to 140 g / L and any value or range between any two of them, for example, it can also be 90 g / L, 100 g / L, 110 g / L, 120 g / L, 130 g / L. When the concentration of sulfuric acid is high, the solubility of copper sulfate in the electrolyte decreases, and it is easy to crystallize and precipitate on the anode, hindering the normal dissolution process of the anode and causing the anode to passivate. When the concentration of sulfuric acid is low, the anode is also easy to passivate. When the concentration of sulfuric acid is in this appropriate range, it is more conducive to electroplating.

[0079] In some embodiments, the mass concentration of chloride ions in the electrolyte is 10 ppm to 25 ppm and any value or range between any two of them, for example, it can also be 12 ppm, 15 ppm, 20 ppm, 22 ppm. Chloride ions can reduce anode polarization, eliminate plating layer stripes in high current density areas, promote the deposition of copper ions, increase cathode polarization, and thus affect the surface brightness of the electrolytic copper foil. Chloride ions can also react with the intermediate product Cu + Special chemical reactions occur, which are closely related to the surface morphology and pimple defects of the copper plating layer. When the concentration of chloride ions is in this range, the surface roughness of the copper plating layer and the generation of burrs can be further reduced, the copper plating layer has better flattening performance and brightness, and in addition, the problem of accelerated equipment corrosion can be solved.

[0080] In the process of configuring the electrolyte, the source of chloride ions can be hydrochloric acid, sodium chloride or potassium chloride.

[0081] In some embodiments, the mass concentration of the leveling agent in the electrolyte is 1 ppm to 15 ppm and any value or range between any two of them, for example, it can also be 5 ppm, 8 ppm, 10 ppm, 12 ppm. The leveling agent can smooth the micro profile of the copper plating layer surface and reduce the surface roughness. Optionally, the leveling agent is a nitrogen-containing compound, and further optionally the leveling agent includes one or more of gelatin, collagen, gentian green and tetrahydrothiazole sulfone and polyethylene imine compounds.

[0082] In some embodiments, the mass concentration of the brightener in the electrolyte is 10 ppm to 60 ppm and any value or range between any two values thereof, for example, it can also be 20 ppm, 30 ppm, 40 ppm, 50 ppm. The brightener can promote grain nucleation and produce a refining grain effect to achieve a bright surface effect. Alternatively, the brightener is an organic divalent sulfide, and further alternatively, the brightener includes one or more of 3-mercapto-1-propane sulfonic acid sodium (English abbreviation MPS), polydisulfide propane sulfonic acid sodium (English abbreviation SPS), bis-(sulfonethyl sulfonic acid sodium)-disulfide (English abbreviation SES) and 1,3-propanedisulfonic acid (English abbreviation PDS).

[0083] In some embodiments, the mass concentration of the wetting agent in the electrolyte is 5 ppm to 20 ppm and any value or range between any two values thereof, for example, it can also be 8 ppm, 10 ppm, 12 ppm, 15 ppm, 18 ppm. The wetting agent promotes bubble escape by reducing the surface tension of the electrode / solution interface, preventing defects such as pinholes. At the same time, the wetting agent can be adsorbed on the electrode surface, increase the cathode polarization, inhibit the deposition rate of copper ions, and make the plated layer crystallize more finely and tightly.

[0084] Chloride ions have a synergistic effect with the leveling agent, the brightener, and the wetting agent, which collectively affect the crystal structure of the copper plating layer. Alternatively, the wetting agent is a polyether compound, and further alternatively, the wetting agent includes one or more of polyethylene glycol (English abbreviation PEG), carboxymethyl cellulose (English abbreviation HEC), and polyvinyl pyrrolidone (English abbreviation PVP).

[0085] In some embodiments, the temperature of the electrolyte during the electrolysis process is 50°C to 60°C.

[0086] In some embodiments, the anode is a titanium substrate, and alternatively, the titanium substrate can be provided with a noble metal coating, such as iridium, tantalum.

[0087] In some embodiments, the cathode is a cathode roller, and the surface material thereof can be high-purity titanium.

[0088] In some embodiments, the above method further includes the step of placing the electrolytic copper foil in a passivation solution for passivation. Alternatively, the passivation solution includes one or more of a chromium source, glucose, and a nitride.

[0089] Further, in some embodiments, the above method further includes one or more of the steps of peeling the copper plating layer from the cathode, washing with water, drying, and coiling.

[0090] In addition, the secondary battery and the power device of the present application are described below.

[0091] Generally, a 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 intercalated and deintercalated between 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.

[0092] The positive electrode sheet

[0093] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector, the positive electrode active material layer including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material layer is disposed on either one or both of the two opposite surfaces of the positive electrode current collector.

[0094] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be 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 obtained by forming a metal material on a polymer material base. In the positive electrode current collector, non-limiting examples of the metal material can include one or more of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, and the like. In the positive electrode current collector, non-limiting examples of the polymer material base can include one or more of a polypropylene (PP) base, a polyethylene terephthalate (PET) base, a polybutylene terephthalate (PBT) base, a polystyrene (PS) base, a polyethylene (PE) base, and the like.

[0095] In some embodiments, the positive electrode active material can be a positive electrode active material for a battery known in the art.

[0096] It is to be noted that the secondary battery according to the present application can be a lithium ion battery, a sodium ion battery.

[0097] As a non-limiting example of a lithium ion battery, the positive active material can include one or more of: lithium-containing phosphates of olivine structure, lithium transition metal oxides, and modified compounds 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, one or more of lithium cobalt oxide (such as LiCoO2), 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 modified compounds thereof. Non-limiting examples of lithium-containing phosphates of olivine structure can include, but are not limited to, one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon. Non-limiting examples of lithium cobalt oxide can include LiCoO2; non-limiting examples of lithium nickel oxide can include LiNiO2; non-limiting examples of lithium manganese oxide can include LiMnO2, LiMn2O4, and the like; non-limiting examples of lithium nickel cobalt manganese oxide can include 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 ), and the like. Non-limiting examples of lithium nickel cobalt aluminum oxide can include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0098] As a sodium ion active material can include one or more of at least one of: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, the present application is not limited to these materials, and other conventional well-known materials that can be used as a positive active material for a sodium ion battery can also be used.

[0099] As an optional technical solution of the present application, the transition metal in the sodium transition metal oxide can be at least one or more of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr and Ce. Non-limiting examples of the sodium transition metal oxide can be NaxMO2, where M can include one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0100] As a non-limiting example of the sodium ion battery, the positive electrode active material can include one or more of the following materials: one or more of sodium transition metal oxides, polyanion compounds and prussian blue compounds. However, the present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium ion batteries can also be used.

[0101] In some embodiments, the positive electrode active material layer can also optionally include a binder. As a non-limiting example, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.

[0102] In some embodiments, the positive electrode active material layer can also optionally include a conductive agent. As a non-limiting example, the conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0103] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode tab can be obtained. The type of the solvent can be selected from, but is not limited to, any of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector. The surface of the positive electrode current collector coated with the positive electrode slurry can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 to 25000 mPa·s. When coating the positive electrode slurry, the coating unit area density based on the dry weight (excluding the solvent) can be 15 to 35 mg / cm 2 . The compaction density of the positive electrode tab can be 3.0 to 3.6 g / cm3 optionally 3.3 to 3.5 g / cm3 3 .

[0104] Negative electrode sheet

[0105] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, the negative active material layer including a negative active material. For example, the negative current collector has two surfaces opposite in the thickness direction thereof, and the negative active material layer is disposed on either one or both of the two surfaces of the negative current collector.

[0106] In the present application, the negative current collector is the electrolytic copper foil of the first aspect of the present application or the electrolytic copper foil prepared by the method of the second aspect of the present application. In some embodiments, the negative active material can be a negative active material for a battery known in the art. As non-limiting examples, the negative active material can include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can include one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can include one or more of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0107] In some embodiments, the negative active material layer can optionally further include a binder. The binder can include one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0108] In some embodiments, the negative active material layer can optionally further include a conductive agent. The conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0109] In some embodiments, the negative active material layer can optionally further include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0110] In some embodiments, the negative electrode sheet can be prepared by dispersing the components described above for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water), to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector; and drying, cold-pressing, or the like, to obtain the negative electrode sheet. The surface of the negative electrode current collector to which the negative electrode slurry is coated can be a single surface of the negative electrode current collector, or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa s to 10000 mPa s. The coating unit area density of the negative electrode slurry, on a dry weight basis (excluding the solvent), can be 75 g / m 2 to 220 g / m 2 . The compaction density of the negative electrode sheet can be 1.0 g / cm 3 to 1.8 g / cm 3 .

[0111] Electrolyte

[0112] The electrolyte has a function of conducting ions between the positive electrode sheet and the negative electrode sheet. The type of the electrolyte is not particularly limited in the present application, and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0113] In some embodiments, the electrolyte uses an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0114] In some embodiments, the electrolyte salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium difluoro-bis-oxalato-phosphate (LiDFOP), and lithium tetrafluoro-oxalato-phosphate (LiTFOP).

[0115] In some embodiments, the solvent can include 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), ethylene carbonate one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), and the like.

[0116] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive that can improve certain performance 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.

[0117] In some embodiments, the additive in the electrolyte solution can include, but is not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethyl ethylene carbonate (TFPC), and the like.

[0118] Separator film

[0119] In some embodiments, the secondary battery further includes a separator film. The type of the separator film is not particularly limited in the present application, and any publicly known porous structure separator film having good chemical stability and mechanical stability can be used.

[0120] In some embodiments, the material of the separator film can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0121] In some embodiments, the thickness of the separator film is 6 μm to 40 μm, and can be optionally 12 μm to 20 μm.

[0122] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator film can be used to make an electrode assembly through a winding process or a stacking process.

[0123] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the electrode assembly and the electrolyte solution described above.

[0124] 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, and the like. 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 further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, and the like.

[0125] The secondary battery includes at least one battery cell. The secondary battery can include one or more battery cells.

[0126] In the present application, a "battery cell" refers to a basic unit capable of converting chemical energy and electrical energy to each other, and further, generally includes at least a positive electrode sheet, a negative electrode sheet, and an electrolyte. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte functions to conduct the active ions between the positive electrode sheet and the negative electrode sheet.

[0127] The shape of the battery cell is not particularly limited in the present application, and can be cylindrical, square, or any other shape.

[0128] In some embodiments, the outer package can include a housing and a cover plate. The housing can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The housing has an opening communicating with the receiving cavity, and the cover plate can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can be wound or stacked to form an electrode assembly. The electrode assembly is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly. The number of electrode assemblies contained in the battery cell can be one or more, and the skilled person can select the appropriate number according to the actual needs.

[0129] The secondary battery can be a battery module or a battery pack.

[0130] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and the skilled person can select the appropriate number according to the application and capacity of the battery module.

[0131] 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, and the skilled person can select the appropriate number according to the application and capacity of the battery pack.

[0132] In addition, the present application also provides a power consuming device, which includes the secondary battery provided by the present application. The secondary battery can be used as a power source of the power consuming device, or as an energy storage unit of the power consuming device. The power consuming device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. The mobile device can be a mobile phone, a notebook computer, etc., for example; the electric vehicle can be 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., but is not limited thereto.

[0133] As a power consuming device, the secondary battery can be selected according to the use requirements thereof.

[0134] 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 demand of the power consuming device for high power and high energy density of the secondary battery, a battery pack or a battery module can be used.

[0135] As another example, the device can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and a secondary battery can be used as a power source.

[0136] Embodiments

[0137] Hereinafter, 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 and should not be understood as a limitation of the present application. In the embodiments, a technique or a condition not mentioned is performed according to a technique or a condition described in a document in the art or according to a product manual. The reagent or the apparatus used is not mentioned by the manufacturer, and is a general product that can be obtained on the market.

[0138] Embodiment 1

[0139] 1) Preparation of electrolyte

[0140] Copper sulfate, sulfuric acid, sodium chloride, a leveling agent, a brightener, and a wetting agent were dissolved in water, and mixed uniformly by sufficient stirring, wherein the concentrations of the respective components were 80 g / L of copper ions, 110 g / L of sulfuric acid, 13 ppm of chloride ions, 45 ppm of MPS (sodium 3-mercapto-1-propane sulfonate), and 35 ppm of SPS (sodium polydithiobispropane sulfonate), 7 ppm of gelatin, and 10 ppm of tetrahydrothiazolidine thione, and 14 ppm of HEC (carboxyethyl cellulose).

[0141] 2) Electrolysis

[0142] The anode plate and the cathode roll to be plated were immersed in the electrolyte described above, the temperature of the electrolyte was 50°C, the flow rate of the electrolyte was 40 m 3 / h, the cathode roll was rotated at a constant speed, copper in the solution was deposited on the surface of the cathode roll to form a copper foil, the thickness of the copper foil was controlled by the cathode current density and the rotation speed of the cathode roll, and a person skilled in the art can control the current density and the rotation speed of the cathode roll by a conventional method to obtain a copper foil with a target thickness. After the copper foil was taken out of the solution with the roll, it was continuously peeled off from the cathode roll, washed with water, dried, and wound to obtain an electrolytic copper foil.

[0143] Embodiments 2 to 7

[0144] The embodiments were basically the same as Embodiment 1, except that the related parameters in the electrolysis process were adjusted, and the details are shown in Table 1.

[0145] Comparative Examples 1 to 8

[0146] The same as Example 1, except that the relevant parameters in the electrolysis process are adjusted, and the details are shown in Table 1.

[0147] Test part

[0148] 1) Tensile strength and elongation of electrolytic copper foil JM ( have the same meaning as above), KAM max ( have the same meaning as above), R ( have the same meaning as above) test

[0149] The microstructure of each sample is observed by electron backscatter diffraction (EBSD), specifically using a C-Swift EBSD detector manufactured by Oxford Instruments, UK. The T JM , KAM max and R values of each sample are obtained by the relevant data and calculation formula obtained by the method. The sample is the cross-section of the electrolytic copper foil along the thickness direction.

[0150] 2) Tensile strength and elongation of electrolytic copper foil

[0151] According to the test method GB / T29847-2013, the HY-0230 universal material testing machine manufactured by Shanghai Hengyi Precision Instrument Co., Ltd. is used to test the tensile strength and elongation of the copper foil at room temperature (about 25°C). The heat treatment is to heat the electrolytic copper foil to 250°C at a rate of 5°C / min, and then reduce to room temperature (25°C) at a rate of 5°C / min after 2 hours of heat treatment at 250°C. Rmi=(R m1 -R m2 ) / R m1 *100%, wherein R m1 and R m2 are the tensile strength of the electrolytic copper foil at room temperature and the tensile strength of the electrolytic copper foil after heat treatment, respectively.

[0152] Table 1

[0153]

[0154]

[0155] The above description of each example tends to emphasize the differences between each example, and the same or similar parts can be referred to each other. For the sake of brevity, the same or similar parts will not be described again.

[0156] Note that the present application is not limited to the above-described embodiments. The above-described embodiments are merely examples, and embodiments having substantially the same configuration, function, and effect as the technical idea of the present application are included in the technical scope of the present application. Furthermore, other modes constructed by applying various modifications to the embodiments, or by combining part of the configurations of the embodiments, which can be conceived by those skilled in the art, without departing from the spirit of the present application, are also included in the scope of the present application.

Claims

1. An electrolytic copper foil, characterized in that, It includes at least one copper layer, wherein the ratio of columnar crystals to equiaxed crystals in a cross-section along the thickness direction of the copper layer is T. JM T JM =N （I＞1） / N （I≤1） Where N is the number of grains, I is the grain aspect ratio calculated using a fitted ellipse from the EBSD grain size measurement data, and the maximum mean grain boundary angle in the cross-section is KAM. max KAM max = Σ(Δφi) / n, where Δφi is the grain boundary angle of each grain boundary, n is the total number of grain boundaries, the grain size in the cross-section is R, and the cross-section satisfies the following conditions (1)~(3): （1）0.2≤T JM ≤0.4； (2) KAM max ≤5.5°; (3) The proportion of grains with R≤0.3μm is 40%~50%, the proportion of grains with R≤0.4μm is 70%~80%, and the proportion of grains with R≤0.5μm is greater than or equal to 95%.

2. The electrolytic copper foil according to claim 1, characterized in that, The copper layer has two surfaces opposite each other in its own thickness direction, namely a first surface and a second surface, and the surface roughness and / or brightness of the first surface and the second surface are different.

3. The electrolytic copper foil according to claim 2, characterized in that, It also includes at least one protective layer, which includes a first protective layer and a second protective layer, wherein the first protective layer is disposed on the first surface and the second protective layer is disposed on the second surface.

4. The electrolytic copper foil according to claim 3, characterized in that, The protective layer contains at least one of chromium, glucose, and nitrides.

5. The electrolytic copper foil according to claim 4, characterized in that, The protective layer contains chromium, and the chromium content in at least one of the protective layers is 20 ppm to 80 ppm.

6. The electrolytic copper foil according to claim 3, characterized in that, The thickness of the first protective layer is 100 nm to 300 nm, and / or the thickness of the second protective layer is 100 nm to 300 nm.

7. The electrolytic copper foil according to claim 1, characterized in that, The thickness of the copper layer is 4μm to 8μm.

8. The electrolytic copper foil according to any one of claims 1 to 7, characterized in that, The electrolytic copper foil has a tensile strength of 60 kgf / mm² at room temperature. 2 ~70 kgf / mm 2 And / or, the elongation of the electrolytic copper foil at room temperature is ≥4.5%, where room temperature is 10℃~40℃.

9. The electrolytic copper foil according to any one of claims 1 to 7, characterized in that, The attenuation rate of the tensile strength of the electrolytic copper foil is Rmi ≤ 3.5%, Rmi = (R m1 -R m2 ) / R m1 *100%, where R m1 and R m2 These are the room temperature tensile strength and the heat treatment temperature of the electrolytic copper foil, respectively. The room temperature is 10℃~40℃, and the heat treatment temperature is 100℃~250℃.

10. A method for preparing electrolytic copper foil according to any one of claims 1 to 9, characterized in that, Includes the following steps: Electrolytic copper foil is obtained by placing the anode and the cathode to be plated in an electrolyte solution for electrolysis. The electrolyte solution contains copper ions, sulfuric acid, chloride ions, leveling agent, brightener, and wetting agent.

11. The method for preparing electrolytic copper foil according to claim 10, characterized in that, The leveling agent is a nitrogen-containing compound, and / or the brightener is an organic divalent sulfide, and / or the wetting agent is a polyether compound.

12. The method for preparing electrolytic copper foil according to claim 11, characterized in that, The nitrogen-containing compounds include one or more of gelatin, collagen, Janus Green, tetrahydrothiazolyl thione, and polyethyleneimine compounds; and / or, the organic divalent sulfides include one or more of sodium 3-mercapto-1-propanesulfonate, sodium polydithiodipropanesulfonate, bis-(sodium sulfoethyl sulfate)-disulfide, and 1,3-propanedisulfonic acid; and / or, the polyether compounds include one or more of polyethylene glycol, carboxyethyl cellulose, and polyvinylpyrrolidone.

13. The method for preparing electrolytic copper foil according to claim 10, characterized in that, The temperature of the electrolyte during the electrolysis process is 50℃~60℃.

14. The method for preparing electrolytic copper foil according to claim 10, characterized in that, It also includes the step of placing the electrolytic copper foil in a passivation solution for passivation.

15. The method for preparing electrolytic copper foil according to claim 14, characterized in that, The passivation solution contains one or more of a chromium source, glucose, and nitrides.

16. A negative electrode sheet, characterized in that, This includes the electrolytic copper foil according to any one of claims 1 to 9, or the electrolytic copper foil prepared by the method according to any one of claims 10 to 15.

17. A secondary battery, characterized in that, Includes the negative electrode sheet as described in claim 16.

18. An electrical appliance, characterized in that, Includes at least one of the secondary batteries described in claim 17.

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