Current collector, electrode sheet, secondary battery, current-consuming device and copper foil

Abstract

Current collector, characterized in that the current collector comprises a copper foil, wherein the average particle size of the crystal grains in the copper foil is 50 nm to 400 nm and the proportion of the number of nanotwins, based on the total number of crystal grains in the copper foil, is greater than or equal to 60%.

Description

Cross-references

[0001] The present application refers to Chinese patent application No. 202410146761.1 entitled “Current collector, electrode sheet, secondary battery, current-consuming device and copper foil and method for producing the copper foil”, which was filed on February 1, 2024 and is hereby incorporated in its entirety by reference. Technical field

[0002] The present application relates to the field of battery technology, in particular a current collector, an electrode sheet, a secondary battery, a current-consuming device, a copper foil and a method for producing the copper foil. State of the art

[0003] In recent years, secondary batteries have been widely used in energy storage systems for hydroelectric, coal, wind and solar power plants, as well as in many different fields such as electric hand tools, electric bicycles, electric motorcycles, electric vehicles, military equipment and aerospace.

[0004] The current collector is a crucial component of secondary batteries. With increasing market demands for the energy density and safety performance of secondary batteries, there is an urgent need to develop lightweight, high-strength current collectors to meet the requirements of the new generation of secondary batteries. Disclosure of the invention

[0005] In light of the above-mentioned topic, the present application aims to provide an extremely thin current collector with excellent mechanical properties, thus meeting the requirements of the new generation of high-performance batteries for current collectors.

[0006] To achieve the above-mentioned tasks, the present application provides a current collector, an electrode sheet, a secondary battery, a current-consuming device, a copper foil, and a method for producing the copper foil.

[0007] A first aspect of the present application provides a current collector comprising a copper foil, wherein the average particle size of the crystal grains in the copper foil is 50 nm to 400 nm, and the proportion of the number of nanotwins, based on the total number of crystal grains in the copper foil, is not less than 60%.

[0008] Twin structures are an effective means of improving the strength and plasticity of metals. Twin boundaries form coherent interfaces with ordered atomic arrangements that, on the one hand, increase resistance to dislocation movement and thus improve material strength, while on the other hand, they can maintain dislocation mobility, thereby strengthening the material without impairing its plasticity. A small crystal grain size can further improve the interfacial structure and thereby increase the additional stress required for dislocation movement across grain boundaries, resulting in work hardening.The high proportion of nanotwin structures and the small crystal grain size together improve the mechanical strength of the copper foil without affecting its high plasticity, thus forming a material basis for further improvements in the energy density and safety of batteries.

[0009] In any embodiment, the average particle size of the crystal grains in the copper foil is 50 nm to 300 nm.

[0010] Copper foil with an average particle size within the aforementioned range can further improve its mechanical strength while maintaining its high plasticity, thus meeting the usage requirements of the new generation of high-energy-density secondary batteries.

[0011] In any embodiment, based on the total number of crystal grains in the copper foil, the proportion of crystal grains with a particle size of less than 200 nm is 20% to 40% and the proportion of crystal grains with a particle size between 200 nm and 500 nm is 50% to 80%.

[0012] In any embodiment, the proportion of the number of crystal grains with a particle size of more than 500 nm, based on the total number of crystal grains in the copper foil, is less than or equal to 5%.

[0013] In the prior art, the production of twin-reinforced copper foil often involves the introduction of micrometer-sized twins, which prevent further improvements in the foil's strength. The copper foil described in the embodiments of the present application exhibits a high proportion of nanotwins, significantly improving its strength. The crystal grains have a small average particle size with an skew distribution, with an extremely low proportion of crystal grains larger than 500 nm. These fine crystal grains reduce the formation of stress concentrations during deformation of the copper foil and promote coordinated grain sliding. This improves elongation at break and simultaneously increases the strength of the copper foil.

[0014] In any embodiment, the proportion of the number of coaxial or quasi-coaxial crystal grains, relative to the total number of crystal grains in the copper foil, is greater than or equal to 80%, wherein the length ratio a1 of the principal axis to the minor axis of the coaxial or quasi-coaxial crystal grains satisfies the condition 1 ≤ a1 < 2.

[0015] A large number of the coaxial or quasi-coaxial crystal grains promotes the isotropy of the copper foil in all directions and contributes to a comprehensive improvement in both the strength and plasticity of the copper foil.

[0016] In any embodiment, the proportion of the number of columnar crystal grains, based on the total number of crystal grains in the copper foil, is less than 10%, wherein the length ratio a2 of the principal axis to the minor axis of the columnar crystal grains satisfies the condition a2 > 2.

[0017] The formation of columnar crystal grains tends to lead to heterogeneity in the mechanical properties of the copper foil. Reducing the proportion of columnar crystal grains contributes to improving the mechanical strength and plasticity of the copper foil and decreases the likelihood of stress concentration points forming.

[0018] In any embodiment, the proportion of the crystal plane diffraction intensity of the (111) texture in the copper foil to the total crystal plane diffraction intensity of the (111) texture, (200) texture, (220) texture, (311) texture and (222) texture in the copper foil is 60% to 85%.

[0019] Common textures for pure copper materials include (111), (200), (220), (311), and (222). According to its crystallographic properties, the high atomic density and mechanical strength of the (111) crystal plane can enhance the twinning effect. Copper foil where the ratio of the crystal plane diffraction intensity of the (111) texture to the total crystal plane diffraction intensity of the (111), (200), (220), (311), and (222) textures in the copper foil is within the range mentioned above is advantageous for improving the mechanical strength and plasticity of the copper foil.

[0020] In any embodiment, the copper foil has a first and a second surface arranged opposite each other. The thickness of the copper foil is denoted as H. The region from the first surface of the copper foil to the thickness range of 0.2 H to 0.5 H is referred to as the first region of the copper foil, and the region from the second surface of the copper foil to the thickness range of 0.2 H to 0.5 H is referred to as the second region of the copper foil. The absolute value of the difference between the average particle size of the crystal grains in the first region and the average particle size of the crystal grains in the second region is less than or equal to 150 nm.

[0021] The crystal grain size and structure of the copper foil are also very uniform along its thickness direction, which forms the basis for it retaining high strength and high plasticity despite its ultra-thin thickness.

[0022] In any embodiment, the proportion of the number of nanotwins, relative to the total number of crystal grains in the copper foil, is 65% to 90%.

[0023] In any embodiment, the maximum surface roughness of the copper foil is less than or equal to 3 µm.

[0024] The copper foil, with a maximum surface roughness of no more than 3 µm, has a smooth and uniform surface and does not tend to form stress concentration points under cyclic loading, which has a positive effect on improving the mechanical strength and plasticity of the copper foil.

[0025] In any embodiment, the thickness H of the copper foil satisfies the condition 3 µm ≤ H ≤ 15 µm.

[0026] The copper foil has a low thickness, which effectively reduces the weight of the battery and further improves the battery's energy density.

[0027] In any embodiment, the tensile strength of the copper foil under test conditions of room temperature, a sample thickness of 6 ± 0.2 µm and a tensile speed of 50 ± 0.5 mm / min is greater than or equal to 600 MPa and the elongation at break of the copper foil is greater than or equal to 4%.

[0028] In any embodiment, the tensile strength of the copper foil under test conditions of room temperature, sample thickness of 6 ± 0.2 µm and tensile speed of 50 ± 0.5 mm / min is 700 MPa to 1500 MPa and the elongation at break of the copper foil is 4.5 % to 10 %.

[0029] The copper foil described above exhibits both high strength and high plasticity, thus meeting the usage requirements of high energy density batteries, improving battery safety and simultaneously increasing the battery's energy density.

[0030] A second aspect of the present application provides an electrode sheet comprising a current collector in any embodiment.

[0031] A third aspect of the present application provides a secondary battery comprising an electrode sheet of the second aspect.

[0032] In any embodiment, the secondary battery can be any type of battery cell, battery module or battery pack.

[0033] In any embodiment, the maximum expansion force of the secondary battery cell is greater than or equal to 1000 kgf.

[0034] In any embodiment, the maximum expansion force of the secondary battery cell is greater than or equal to 2500 kgf.

[0035] In any embodiment, the maximum expansion force of the secondary battery cell is greater than or equal to 4000 kgf. The current collector in the prior art tends to break under the high expansion force of the secondary battery, leading to safety accidents and limiting further improvements in the electrochemical performance of the secondary battery. The current collector provided in the embodiments of the present application exhibits both excellent tensile strength and elongation at break, making it suitable for secondary batteries with high expansion forces and contributing to a further improvement in the energy density of the secondary battery.

[0036] A fourth aspect of the present application provides a power-consuming device comprising a secondary battery of the third aspect.

[0037] A fifth aspect of the present application provides a method for producing a copper foil, wherein the copper foil is produced by means of an electroplating process, wherein the electroplating process in particular comprises periodically applying a current to an electroplating solution to reduce and deposit copper ions in the electroplating solution and thereby form the copper foil, wherein the average particle size of the crystal grains in the copper foil is 50 nm to 400 nm, and the proportion of the number of nanotwins, based on the total number of crystal grains in the copper foil, is greater than or equal to 60%.

[0038] In any embodiment, the current is a pulse current, wherein the pulse current comprises one or more of square wave pulse currents, sine wave pulse currents, triangle wave pulse currents and sawtooth wave pulse currents.

[0039] By applying a pulsed current to the electroplating solution, the nucleation and grain growth process of the reduced copper ions can be controlled by switching the current on and off. This inhibits grain growth and results in the formation of uniform nanocrystal grains, improving the tensile strength and elongation at break of the copper foil. Compared to conventional direct current deposition, pulsed current deposition allows for a higher peak current density, which promotes large-area nucleation of the copper foil. This increases the density of the copper foil and reduces the crystal grain size, thereby improving the mechanical strength of the copper foil.

[0040] In any embodiment, the electroplating solution comprises an additive, wherein the additive comprises one or more leveling agents, wetting agents and glazing agents.

[0041] In any embodiment, the additive comprises the leveling agent, the wetting agent, and the glazing agent.

[0042] The leveling agent adheres to the tip of the copper foil with a rapid deposition rate, inhibits grain growth, and evens out the growth rate of depressions and peaks to improve the flatness of the copper foil. The wetting agent improves the wettability between the electroplating solution and the substrate. Sufficient wettability of the electroplating solution on the cathode enables rapid electroplating even at high currents, increases the nucleation rate of the copper foil, and reduces the average particle size of the crystal grains in the copper foil. A specific amount of brightening agent can refine the crystal grain size of the copper foil, reduce its surface roughness, and improve its smoothness.

[0043] In any embodiment, the concentration of the leveling agent in the electroplating solution is 20 mg / L to 300 mg / L.

[0044] In any embodiment, the concentration of the leveling agent in the electroplating solution is 50 mg / L to 150 mg / L.

[0045] In any embodiment, the concentration of the wetting agent in the electroplating solution is 10 mg / L to 200 mg / L.

[0046] In any embodiment, the concentration of the wetting agent in the electroplating solution is 30 mg / L to 100 mg / L.

[0047] In any embodiment, the concentration of the brightening agent in the electroplating solution is 10 mg / L to 200 mg / L.

[0048] In any embodiment, the concentration of copper ions in the electroplating solution is 30 g / L to 100 g / L.

[0049] In any embodiment, the concentration of copper ions in the electroplating solution is 45 g / L to 75 g / L.

[0050] The research results show that the combination of low copper ion concentration and high additive concentration, compared to a combination of high copper ion concentration and low additive concentration, contributes to improving the strength and elongation at break of the copper foil. Furthermore, the low copper ion concentration helps to reduce concentration difference polarization, control crystal grain growth and deposition rate, promote the formation of small crystal grains, and improve the mechanical strength of the copper foil.

[0051] In any embodiment, the concentration of chloride ions in the electroplating solution is 10 mg / L to 80 mg / L.

[0052] In any embodiment, the pH value of the electroplating solution is 2.5 to 4.4.

[0053] In any embodiment, the leveling agent comprises one or more of gelatin and Janus green; the wetting agent comprises one or more of hydroxyethylcellulose and polyethylene glycol; and the glazing agent comprises one or more of bis(sodium sulfopropyl)disulfide, sodium 3-mercapto-1-propanesulfonate and thiourea.

[0054] In any embodiment, the wetting agent comprises hydroxyethylcellulose and polyethylene glycol.

[0055] The research results show that the simultaneous addition of two different wetting agents can improve the mechanical strength of the copper foil more effectively than the addition of only one type of wetting agent. Although the mechanism is not yet clear, it is speculated that this is related to the competitive adsorption between the two different types of additives, which positively affects the consistency of the crystal grains during the deposition process, reduces the variation in crystal grain size in the thickness direction, and improves the uniformity of the copper foil.

[0056] In any embodiment, the mass concentration ratio of copper ions to leveling agent is 500 : 1 to 4500 : 1; and / or the mass concentration ratio of copper ions to brightening agent is 300 : 1 to 6000 : 1.

[0057] In some embodiments, the electroplating solution comprises gelatin at a concentration of 20 mg / L to 150 mg / L, polyethylene glycol at a concentration of 15 mg / L to 100 mg / L, hydroxyethylcellulose at a concentration of 10 mg / L to 80 mg / L, bis-(sodium sulfopropyl)disulfide at a concentration of 15 mg / L to 150 mg / L, copper ions at a concentration of 45 g / L to 90 g / L, and chloride ions at a concentration of 10 mg / L to 80 mg / L.

[0058] In any embodiment, the peak current density of the impulse current is denoted as I, with the unit A / dm². 2 ; the duty cycle of the pulse current is denoted as s, where the peak current density I and the duty cycle s are given by the condition 2 A / dm² 2 ≤ I × s ≤ 18 A / dm 2 fulfill.

[0059] The product of the peak current density I and the duty cycle s corresponds to the average current density within a pulse cycle. With pulsed current deposition, the average current density within the pulse cycle can be higher than the maximum achievable current density with direct current deposition, since an excessively high direct current deposition density can lead to hydrogen evolution and concentration difference polarization in the electroplating solution, thereby reducing the uniformity of the copper foil during the electroplating process. Within the aforementioned range, the product of the peak current density I and the duty cycle s can not only effectively reduce the particle size of the crystal grains but also improve the uniformity of the crystal grain size in the thickness direction of the produced copper foil.The product of the peak current density I and the duty cycle s within the aforementioned range, in combination with a low copper ion concentration in the electroplating solution, can further improve the concentration difference polarization of the electroplating solution, achieve the production of small crystal grains, and improve the tensile strength and elongation at break of the copper foil. In any embodiment, the peak current density I of the pulsed current satisfies the condition of 3.3 A / dm. 2 ≤ I ≤ 333 A / dm 2 .

[0060] In any embodiment, the duty cycle s of the pulse current satisfies the condition 2% ≤ s ≤ 50%.

[0061] In any embodiment, the pulse width of the pulse current is 1 ms to 50 ms.

[0062] In any embodiment, the distance between the cathode electrode and the anode electrode is 15 mm to 20 mm.

[0063] In any embodiment, the deposition temperature is between 45 °C and 60 °C.

[0064] In any embodiment, the deposition time is greater than or equal to 80 seconds.

[0065] In any embodiment, the electroplating process particularly comprises the periodic application of a pulsed current to the electroplating solution to reduce and deposit copper ions in the electroplating solution; wherein the peak current density I of the pulsed current meets the condition 100 A / dm² 2 ≤ I ≤ 180 A / dm 2 fulfilled, the duty cycle s of the pulse current meets the condition 2 % ≤ s ≤ 10 % and the deposition time is 80 s to 250 s.

[0066] In any embodiment, the manufacturing process is a continuous production process.

[0067] A sixth aspect of the present application provides a copper foil which has the same characteristics as the copper foil in the aforementioned current collector, which will not be discussed again here.

[0068] In any embodiment, the copper foil is produced by a manufacturing process of the fifth aspect.

[0069] In any embodiment, the maximum width of the copper foil is greater than or equal to 1.5 meters and / or the maximum length of the copper foil is greater than or equal to 10000 meters.

[0070] This copper foil can be produced in large dimensions and has prospects for industrial application. Brief description of the drawings

[0071] To better illustrate the technical solutions in the embodiments of the present application, a brief description of the drawings required in these embodiments is given below. Of course, the drawings described below represent only some embodiments of the present application, and other drawings can be prepared by a person skilled in the art based on these drawings without any creative effort. Fig. Figure 1 is a schematic diagram of the particle size distribution of the crystal grains of the copper foil from embodiment 1 of the present application; Fig. Figure 2 is an inverse pole figure distribution diagram of the electron backscatter diffraction pattern of the copper foil from embodiment 1 of the present application; Fig. Figure 3 is a diagram of the tensile force-strain curve of the copper foil from embodiment 1 of the present application; Fig. 4a is an X-ray diffraction diagram of the copper foil from embodiment 2 of the present application; Fig. 4b is an X-ray diffraction diagram of the copper foil from comparative example 1 of the present application; Fig. Figure 5 is a schematic diagram of an embodiment of a secondary battery of the present application; Fig. Figure 6 is a schematic exploded view of an embodiment of a secondary battery of the present application; Fig. Figure 7 shows a schematic representation of an embodiment of a battery module of the present application; Fig. Figure 8 shows a schematic representation of an embodiment of a battery pack of the present application; Fig. Figure 9 is a schematic exploded view of the embodiment of the in Fig. 8 battery packs shown; Fig.Figure 10 shows a schematic representation of an embodiment of a power-consuming device which includes the secondary battery of the present application as a power source;

[0072] The drawings are not necessarily to scale. Reference symbols are as follows: 1, battery pack; 2, upper housing; 3, lower housing; 4, battery module; 5, secondary battery; 51, housing body; 52, electrode assembly; 53, cover plate. Detailed descriptions

[0073] The embodiments of a current collector, an electrode sheet, a secondary battery, a current-consuming device, a copper foil, and a method for producing the copper foil of the present application are described in detail below with appropriate reference to the accompanying drawings. However, an unnecessarily detailed description can be omitted. For example, a detailed description of known facts and a repeated description of essentially the same structure can be avoided. This is to prevent the following description from becoming unnecessarily long-winded, thus facilitating understanding by those skilled in the art. Furthermore, the drawings and the following description serve to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0074] The “range” disclosed in the present application is defined in terms of a lower bound and an upper bound. A given range is defined by selecting a lower bound and an upper bound. The selected lower bound and upper bound define the limits of the specific range. The ranges thus defined may or may not include the end values ​​and may be specified in any combination; that is, any lower bound can be combined with any upper bound to form a range. For example, if, for a particular parameter, the ranges of 60 to 120 and 80 to 110 are listed, the ranges of 60 to 110 and 80 to 120 are also conceivable. If, in addition, minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are listed, all of the following ranges are conceivable: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5.In the present application, unless otherwise specified, a range of numbers "a to b" represents an abbreviation for any combination of real numbers between a and b, where a and b are both real numbers. For example, the range "0 to 5" means that all real numbers between "0 to 5" are listed therein, and "0 to 5" is simply an abbreviation for these number combinations. Furthermore, if a particular parameter is specified as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0075] Unless otherwise stated, all embodiments and optional embodiments of the present application may be combined to form new technical solutions, and such technical solutions should be considered to be contained in the disclosure of the present application.

[0076] Unless otherwise stated, all technical features and optional technical features of the present application can be combined to form new technical solutions, and such technical solutions should be considered to be contained in the disclosure of the present application.

[0077] Unless otherwise stated, all steps of the present application may be carried out sequentially or in any order, but preferably sequentially. For example, "the method comprises steps (a) and (b)" means that the method may comprise steps (a) and (b) carried out sequentially, or that it may comprise steps (b) and (a) carried out sequentially. For example, the aforementioned method may further comprise step (c), which means that step (c) may be added in any order. For example, the method may comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0078] Unless otherwise stated, the terms “comprise” and “contain” used in this application may be interpreted as either open or closed. For example, the terms “comprise” and “contain” may mean that they may also include or contain other, unlisted components, or that they may only include or contain the listed components.

[0079] Unless otherwise specified, the term "or" in this application means an inclusive "or". For example, the expression "A or B" means "A, B, or both A and B". More precisely, the condition "A or B" is satisfied if any of the following conditions are true: 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).

[0080] Unless otherwise stated, the terms used in this application have the generally known meanings which are usually understood by the person skilled in the art.

[0081] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured using various test methods commonly used in the art. For example, they can be measured according to the test methods specified in this application. In particular, during the test, the microstructure of the copper foil as a whole is characterized by means of sampling areas.

[0082] Unless otherwise specified, the term ‘active ions’ in the present application refers to ions that can be intercalated and deintercalated between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions.

[0083] In the present application, the terms “several” and “different” refer to two or more.

[0084] With the increasing energy density of secondary batteries, there is a need for thinner and lighter current collectors for electrode sheets. Reducing the thickness of the current collector significantly decreases its maximum load capacity, and the thickness available for plastic deformation is also greatly reduced. This leads to a substantial decrease in the current collector's tensile strength and elongation at break. Consequently, current collectors of standard strength in the prior art are already barely able to meet the operational requirements of secondary batteries. Furthermore, after thinning, current collectors of standard strength are prone to fatigue fracture in the late cycle phase of secondary batteries, which in turn leads to thermal uncontrollability of the cell and causes safety hazards. Therefore, it is essential to effectively improve the tensile strength and plasticity (elongation at break) of the current collector while simultaneously making it lighter and thinner.

[0085] In current metal strengthening technology, strength is typically increased primarily through the introduction of incoherent grain or phase boundaries, which impede dislocation movement. Introducing a large number of incoherent grain boundaries into a material significantly increases its strength. However, with the continuous increase in these "obstacles" to dislocation movement, dislocation motion within the lattice becomes severely restricted or even completely suppressed. This prevents coordinated plastic deformation, resulting in brittleness. Consequently, the enhancement of the mechanical properties of metallic materials often comes at the expense of plasticity, while materials with excellent plasticity tend to exhibit very low strength.

[0086] On this basis, the present application provides a current collector comprising a copper foil, wherein the average particle size of the crystal grains in the copper foil is 50 nm to 400 nm, and the proportion of the number of nanotwins, based on the total number of crystal grains in the copper foil, is greater than or equal to 60%.

[0087] In this document, the term "twins" refers to two crystals (or two parts of a crystal) that form a mirror-symmetric alignment along a common crystal plane (i.e., a specific orientation relationship). These two crystals are called "twins," and the common crystal plane is called the twin plane. Twins whose size in all dimensions is less than 1000 nanometers are called nanotwins.

[0088] The average particle size of the crystal grains on the copper foil can be determined using methods known in engineering. One example is the measurement of the cross-sectional area of ​​the copper foil using a combination of electron backscatter diffraction (EBSD) and scanning electron microscopy. A copper foil with an area of ​​at least 5 mm × 5 mm and at most 8 mm × 8 mm is selected to obtain an inverse pole figure distribution diagram of the copper foil. The average diameter of the equivalent circle of the crystal grains is used as the particle size of the crystal grains, and the particle sizes of the crystal grains within this area are statistically recorded to create a number distribution diagram, as shown in [reference to be added]. Fig.Figure 1 shows the following. A skewness distribution is used for fitting, and the length corresponding to the peak value is used as the average particle size of the crystal grains.

[0089] In some embodiments, the average particle size of the crystal grains of the copper foil is optionally 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm or 400 nm, or lies in a range between any two of these.

[0090] In some embodiments, the average particle size of the crystal grains of the copper foil is 50 nm to 300 nm.

[0091] Copper foil with an average particle size within the aforementioned range can further improve its mechanical strength while maintaining its high plasticity, thus meeting the usage requirements of the new generation of high-energy-density secondary batteries.

[0092] In some embodiments, based on the total number of crystal grains in the copper foil, the proportion of crystal grains with a particle size of less than 200 nm is 20% to 40% and the proportion of crystal grains with a particle size between 200 nm and 500 nm is 50% to 80%.

[0093] In some embodiments, the proportion of the number of crystal grains with a particle size of less than 200 nm, relative to the total number of crystal grains in the copper foil, is optionally 20%, 24%, 28%, 32%, 36% or 40%, or lies in a range between any two of these values.

[0094] In some embodiments, the proportion of the number of crystal grains with a particle size between 200 nm and 500 nm, relative to the total number of crystal grains in the copper foil, is optionally 50%, 55%, 60%, 65%, 70%, 75% or 80%, or lies in a range between any two of these.

[0095] In some embodiments, the proportion of the number of crystal grains with a particle size greater than 500 nm, relative to the total number of crystal grains in the copper foil, is less than or equal to 5%, optionally less than or equal to 2%.

[0096] In some embodiments, the proportion of the number of crystal grains with a particle size greater than 500 nm, relative to the total number of crystal grains in the copper foil, is optionally 0.5%, 1%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, or lies in a range between any two of these.

[0097] The crystal grains of the copper foil provided in the embodiments of the present application have a small average particle size with an skew distribution, wherein the proportion of crystal grains with a particle size greater than 500 nm is extremely low. The fine crystal grains reduce the formation of stress concentrations during deformation of the copper foil and promote the coordinated sliding of crystal grains. This improves the elongation at break and simultaneously increases the strength of the copper foil.

[0098] In the present application, the proportion of nanotwins can be determined using methods known in the art. As an example, the cross-section of the copper foil is observed using a combination of electron backscatter diffraction (EBSD) and scanning electron microscopy. A copper foil with an area of ​​at least 5 mm × 5 mm and at most 8 mm × 8 mm is selected to obtain an inverse pole figure distribution diagram of the copper foil, where different colors represent different orientations of crystal grains. Fig.Figure 2, for example, shows that the red lines within the crystal grains represent twin boundaries, indicating the presence of twin structures. The size and number of twins can be statistically determined using analysis software associated with the electron backscatter diffraction instrument, allowing the proportion of nanotwins to be calculated. As an example, the features of the crystal grains were analyzed using an Oxford C-Nano+ electron backscatter diffraction instrument and its associated software.

[0099] In some embodiments, the proportion of the number of nanotwins, relative to the total number of crystal grains in the copper foil, is optionally 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, or lies in a range between any two of these.

[0100] Twin structures are an effective means of improving the strength and plasticity of metals. The twin boundaries form coherent interfaces with ordered atomic arrangements that, on the one hand, increase resistance to dislocation movement and thus improve material strength, while on the other hand, they can maintain dislocation mobility, thereby strengthening the material without impairing its plasticity. However, in the prior art, the production of twin-reinforced copper foil often introduces micrometer-sized twins, which prevent further improvements in the copper foil's strength. The copper foil provided in the embodiment of the present application has a high proportion of nanotwins, which significantly improves the copper foil's strength and simultaneously enhances its plasticity.A small crystal grain size can further improve the interfacial structure and thereby increase the additional stress required for the displacement of dislocations across grain boundaries, resulting in material strengthening. The high proportion of nanotwin structures and the small crystal grain size together improve the mechanical strength of the copper foil without compromising its high plasticity, thus forming a material basis for further improvements in the energy density and safety of batteries.

[0101] In this document, the term "equiaxial or quasi-equiaxial crystal grains" refers to crystal grains whose major and minor axes are the same or hardly distinguishable. In some embodiments, the length ratio a1 of the major axis to the minor axis of the equiaxial or quasi-equiaxial crystal grains satisfies the condition 1 ≤ a1 < 2.

[0102] In some embodiments, the proportion of the number of coaxial or quasi-coaxial crystal grains, relative to the total number of crystal grains in the copper foil, is greater than or equal to 80%, optionally greater than or equal to 90%, wherein the length ratio a1 of the principal axis to the minor axis of the coaxial or quasi-coaxial crystal grains satisfies the condition 1 ≤ a1 < 2.

[0103] In the present application, the proportion of coaxial or quasi-coaxial crystal grains can be determined using methods known in the art. As an example, the cross-section of the copper foil is observed using a combination of electron backscatter diffraction (EBSD) and scanning electron microscopy. A copper foil with an area of ​​at least 5 mm × 5 mm and at most 8 mm × 8 mm is selected to obtain an inverse pole figure distribution diagram of the copper foil. The proportion of coaxial or quasi-coaxial crystal grains is determined using analysis software.

[0104] A large number of the coaxial or quasi-coaxial crystal grains contributes to achieving the refinement and homogenization of the crystal grains in the copper foil, and the properties of the coaxial or quasi-coaxial crystal grains are the same or similar in all directions, which contributes to comprehensively improving the strength and plasticity of the copper foil.

[0105] In some embodiments, the proportion of the number of coaxial or quasi-coaxial crystal grains, relative to the total number of crystal grains in the copper foil, is 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99% or 100%, or lies in a range between any two of these values.

[0106] In some embodiments, the proportion of columnar crystal grains, based on the total number of crystal grains in the copper foil, is less than 10%, wherein the length ratio a2 of the principal axis to the minor axis of the columnar crystal grains satisfies the condition a2 > 2.

[0107] The formation of columnar crystal grains tends to lead to heterogeneity in the mechanical properties of the copper foil. Reducing the proportion of columnar crystal grains contributes to improving the mechanical strength and plasticity of the copper foil and decreases the likelihood of stress concentration points forming.

[0108] In some embodiments, the main axis direction of the columnar crystal grains is the thickness direction of the copper foil.

[0109] In some embodiments, the proportion of the crystal plane diffraction intensity of the (111) texture in the copper foil to the total crystal plane diffraction intensity of the (111) texture, (200) texture, (220) texture, (311) texture and (222) texture in the copper foil is greater than or equal to 60%, optionally 60% to 85%.

[0110] In this document, the term "texture" refers to the phenomenon that during crystal formation, the crystal grains in a polycrystal arrange themselves in an ordered manner along certain directions, exhibiting a more or less statistically uneven distribution; that is, they aggregate and align themselves in certain directions, thereby significantly increasing the probability of orientation in these directions, which is also referred to as preferred orientation or favored orientation.

[0111] In the present application, the crystal plane diffraction intensity of the texture in the copper foil can be determined using methods known in the art. As an example, the copper foil is tested with an X-ray diffractometer. With reference to the X-ray spectrum of the reference copper powder (PDF No.04-0836) the peak area of ​​the diffraction peak with a peak position between 40° and 45° is used as the crystal plane diffraction intensity of the (111) texture, the peak area of ​​the diffraction peak with a peak position between 47° and 52° as the crystal plane diffraction intensity of the (200) texture, the peak area of ​​the diffraction peak with a peak position between 70° and 75° as the crystal plane diffraction intensity of the (220) texture, the peak area of ​​the diffraction peak with a peak position between 85° and 95° as the crystal plane diffraction intensity of the (311) texture and the peak area of ​​the diffraction peak with a peak position between 103° and 107° as the crystal plane diffraction intensity of the (222) texture.

[0112] In some embodiments, the proportion of the crystal plane diffraction intensity of the (111) texture in the copper foil to the total crystal plane diffraction intensity of the (111) texture, (200) texture, (220) texture, (311) texture and (222) texture in the copper foil is optionally 60%, 65%, 70%, 75%, 80% or 85% or lies in a range of values ​​between any two thereof.

[0113] Common textures for pure copper materials include (111), (200), (220), (311), and (222). According to its crystallographic properties, the high atomic density and mechanical strength of the (111) crystal plane can enhance the twin-strength effect. A high proportion of the (111) texture in the copper foil contributes to increasing the effects of mechanical strengthening and plasticity improvement of the copper foil.

[0114] In some embodiments, the copper foil has a first and a second surface arranged opposite each other. The thickness of the copper foil is denoted as H. The area from the first surface of the copper foil to the thickness range of 0.2 H to 0.5 H is referred to as the first region of the copper foil, and the area from the second surface of the copper foil to the thickness range of 0.2 H to 0.5 H is referred to as the second region of the copper foil. The absolute value of the difference between the average particle size of the crystal grains in the first region and the average particle size of the crystal grains in the second region is less than or equal to 150 nm.

[0115] In some embodiments, the absolute value of the difference between the average particle size of the crystal grains in the first area and the average particle size of the crystal grains in the second area is optionally 1 nm, 20 nm, 40 nm, 60 nm, 80 nm, 100 nm, 120 nm, 140 nm or 150 nm, or lies in a range of values ​​between any two of these.

[0116] The crystal grain size and structure of the copper foil are also very uniform along its thickness direction, indicating that consistent deposition was achieved across different deposition times. Furthermore, the electroplating solution did not undergo any apparent polarization during the deposition process, which suggests that the copper foil retains high strength and plasticity despite its ultrathin thickness.

[0117] In some embodiments, the proportion of the number of nanotwins, relative to the total number of crystal grains in the copper foil, is 65% to 90%.

[0118] In some embodiments, the maximum surface roughness of the copper foil is less than or equal to 3 µm.

[0119] The maximum surface roughness of the copper foil reflects its uniformity and smoothness. This roughness can be determined using established methods, such as a stylus measuring device. The foil surface is wiped with alcohol, placed securely on a horizontal surface, and the stylus is applied. The probe tip is brought into contact with the foil surface and carefully drawn across it. The roughness is then measured. The test was repeated five times at different points on the foil, and the highest measured value was considered the maximum surface roughness.

[0120] In some embodiments, the maximum surface roughness of the copper foil is optionally 0.1 µm, 0.5 µm, 1 µm, 1.5 µm, 2 µm, 2.5 µm or 3 µm, or lies in a range of values ​​between any two of these.

[0121] The copper foil with a maximum surface roughness of less than or equal to 3 µm has a smooth and uniform surface on which stress concentration points do not easily form under cyclic loading, which has a positive effect on improving the mechanical strength and plasticity of the copper foil.

[0122] In some embodiments, the thickness H of the copper foil meets the condition 3 µm ≤ H ≤ 15 µm, optionally 3 µm ≤ H ≤ 8 µm.

[0123] In some embodiments, the thickness H of the copper foil is optionally 3 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, 9 µm, 10 µm, 11 µm, 12 µm, 13 µm, 14 µm or 15 µm, or lies in a range of values ​​between any two of these.

[0124] In the present application, the thickness of the copper foil can be determined using methods known in the art. As an example, a 20 cm thickness is described. 2 × 15 cm 2 A large sample was cut out, and the cut-out sample strip was weighed on an electronic balance to determine its weight. The volume of the sample strip was then calculated based on the density ρ of the copper foil, which is 8.96 g / cm³. 3 calculated. Since the length and width of the test strip are known, its thickness can be derived from them.

[0125] The copper foil has a low thickness, which effectively reduces the weight of the battery and further improves the battery's energy density.

[0126] In some embodiments, the tensile strength of the copper foil under test conditions of room temperature, a sample thickness of 6 ± 0.2 µm and a tensile speed of 50 ± 0.5 mm / min is greater than or equal to 600 MPa and the elongation at break of the copper foil is greater than or equal to 4%; optionally, the tensile strength of the copper foil is 700 MPa to 1500 MPa and further optionally 800 MPa to 1000 MPa; the elongation at break of the copper foil is 4.5% to 10% and further optionally 5% to 8%.

[0127] In this document, the term "room temperature" refers to 20 ± 10 °C.

[0128] In this document, the term "tensile strength" refers to the maximum load-bearing capacity per unit area of ​​a sample when it is continuously loaded until it breaks.

[0129] In this document, the term "elongation at break" refers to the ratio of the change in length of a material during plastic deformation up to fracture after loading to its original length. It is usually expressed as a percentage and is an important parameter for assessing a material's ability to deform under tension during tensile stress.

[0130] In the present application, the tensile strength and elongation at break of the copper foil can be determined using methods known in the art, for example, according to standard GB / T 5230-1995 "Electrolytic copper foil". As an example, at least four samples are cut to lengths of 200 ± 0.5 mm, widths of 15 ± 0.25 mm, and thicknesses of 6 ± 0.2 µm. At room temperature, the samples are continuously subjected to a tensile load of 50 ± 0.5 mm / min until they break. The tensile strength of the sample is determined by dividing the maximum load by the cross-sectional area of ​​the sample. The cross-sectional area of ​​the sample can be calculated by dividing the mass of the sample by the product of its length and density. The density of the copper foil sample can be assumed to be 8.9 g / cm³. 3 be accepted.

[0131] In some embodiments, under test conditions of room temperature, a sample thickness of 6 ± 0.2 µm and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is optionally 600 MPa, 700 MPa, 800 MPa, 900 MPa, 1000 MPa, 1100 MPa, 1200 MPa, 1300 MPa, 1400 MPa or 1500 MPa or lies in a range between any two of these values; the elongation at break of the copper foil is optionally 4%, 4.5%, 5%, 6%, 7%, 8%, 9% and 10% or lies in a range between any two of these values.

[0132] The copper foil described above exhibits both high strength and high plasticity, thus meeting the usage requirements of high energy density batteries, improving battery safety and simultaneously increasing the battery's energy density.

[0133] The present application further provides a method for producing a copper foil, wherein the copper foil is produced by means of an electroplating process, the electroplating process comprising periodically applying a current to an electroplating solution to reduce and deposit copper ions in the electroplating solution and thereby forming the copper foil, wherein the average particle size of the crystal grains in the copper foil is 50 nm to 400 nm, and the proportion of the number of nanotwins, based on the total number of crystal grains in the copper foil, is greater than or equal to 60%, optionally greater than or equal to 65%.

[0134] In this document, the term "galvanizing process" refers to a process for depositing metal or alloys onto the surface of a workpiece using the electrolysis principle to form a metal layer.

[0135] In some embodiments, the current is a pulsed current, wherein the pulsed current comprises one or more of square wave pulsed currents, sine wave pulsed currents, triangle wave pulsed currents and sawtooth wave pulsed currents.

[0136] In some embodiments, the pulse current includes a rectangular wave pulse current.

[0137] In this document, the term "impulse current" refers to current or voltage pulses that occur periodically.

[0138] By applying a pulsed current to the electroplating solution, the nucleation and grain growth process of the reduced copper ions can be controlled by switching the current on and off. This inhibits grain growth and results in the formation of uniform nanocrystal grains, improving the tensile strength and elongation at break of the copper foil. Compared to conventional direct current deposition, pulsed current deposition allows for a higher peak current density, which promotes large-area nucleation of the copper foil. This increases the density of the copper foil and reduces the crystal grain size, thereby improving the mechanical strength of the copper foil.

[0139] In some embodiments, the electroplating solution includes copper ions and chloride ions.

[0140] In some embodiments, the concentration of copper ions in the electroplating solution is 30 g / L to 100 g / L, optionally 45 g / L to 75 g / L.

[0141] In some embodiments, the concentration of copper ions in the electroplating solution is 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L or 100 g / L, or lies in a range between any two of these values.

[0142] The research results show that the combination of low copper ion concentration and high additive concentration, compared to a combination of high copper ion concentration and low additive concentration, contributes to improving the strength and elongation at break of the copper foil. Furthermore, the low copper ion concentration helps control the growth and deposition rate of the crystal grains, which promotes the production of small crystal grains and improves the mechanical strength of the copper foil.

[0143] In some embodiments, the concentration of chloride ions is 10 mg / L to 80 mg / L.

[0144] In some embodiments, the concentration of chloride ions is 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L or 80 mg / L, or lies in a range between any two of these values.

[0145] In some embodiments, the electroplating solution also includes an additive, wherein the additive comprises one or more leveling agents, wetting agents and brightening agents.

[0146] In this document, the term "leveling agent" refers to a substance added to the electroplating solution to improve the evenness of the coating.

[0147] In this document, the term "wetting agent" refers to a substance used to reduce the interfacial tension between the electroplating solution and the electrodes, thereby improving the adhesion of the coating to the substrate.

[0148] In this document, the term "glossing agent" refers to a substance that improves the smoothness of the coating and reduces surface roughness.

[0149] The leveling agent adheres to the tip of the copper foil with a rapid deposition rate, inhibits grain growth, and evens out the growth rate of depressions and peaks to improve the flatness of the copper foil. The wetting agent improves the wettability between the electroplating solution and the substrate. Sufficient wettability of the electroplating solution on the cathode enables rapid electroplating even at high currents, increases the nucleation rate of the copper foil, and reduces the average particle size of the crystal grains in the copper foil. The brightening agent refines the crystal grain size of the copper foil, reduces the surface roughness, and improves the surface smoothness.

[0150] In some embodiments, the additive includes the leveling agent, the wetting agent, and the glazing agent.

[0151] The research results show that the simultaneous addition of several additives can create a synergistic effect and effectively improve the strength and plasticity of copper foil.

[0152] In some embodiments, the leveling agent comprises one or more of gelatin and Janus green; the wetting agent comprises one or more of hydroxyethylcellulose and polyethylene glycol; the glazing agent comprises one or more of bis(sodium sulfopropyl)disulfide, sodium 3-mercapto-1-propanesulfonate and thiourea.

[0153] In some embodiments, the wetting agent comprises hydroxyethylcellulose and polyethylene glycol.

[0154] The research results show that the simultaneous addition of two different wetting agents can improve the mechanical strength of the copper foil more effectively than the addition of only one type of wetting agent. Although the mechanism is not yet clear, it is speculated that this is related to the competitive adsorption between the two different types of additives, which positively affects the consistency of the crystal grains during the deposition process, reduces the variation in crystal grain size in the thickness direction, and improves the uniformity of the copper foil.

[0155] In some embodiments, the concentration of the leveling agent in the electroplating solution is 20 mg / L to 300 mg / L, optionally 50 mg / L to 150 mg / L.

[0156] In some embodiments, the concentration of the leveling agent in the electroplating solution is 20 mg / L, 50 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L or 300 mg / L, or lies in a range between any two of these values.

[0157] In some embodiments, the concentration of the wetting agent in the electroplating solution is 10 mg / L to 200 mg / L, optionally 30 mg / L to 100 mg / L.

[0158] In some embodiments, the concentration of the wetting agent in the electroplating solution is 10 mg / L, 30 mg / L, 50 mg / L, 80 mg / L, 100 mg / L, 130 mg / L, 150 mg / L, 180 mg / L or 200 mg / L, or lies in a range between any two of these values.

[0159] In some embodiments, the concentration of the brightening agent in the electroplating solution is 10 mg / L to 200 mg / L.

[0160] In some embodiments, the concentration of the brightening agent in the electroplating solution is 10 mg / L, 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L, 110 mg / L, 120 mg / L, 130 mg / L, 140 mg / L, 150 mg / L, 160 mg / L, 170 mg / L, 180 mg / L, 190 mg / L or 200 mg / L, or lies in a range between any two of these values.

[0161] In some embodiments, the pH value of the electroplating solution is 2.5 to 4.4.

[0162] In some embodiments, the pH value of the electroplating solution is 2.5, 2.7, 2.9, 3.1, 3.3, 3.5, 3.7, 3.9, 4.1 or 4.4, or lies within a range between any two of these values.

[0163] In some embodiments, the mass concentration ratio of copper ions to leveling agent is 500 : 1 to 4500 : 1; and / or the mass concentration ratio of copper ions to brightening agent is 300 : 1 to 6000 : 1.

[0164] In some embodiments, the mass concentration ratio of copper ions to leveling agent is optionally 500:1, 1000:1, 1500:1, 2000:1, 2500:1, 3000:1, 3500:1, 4000:1 or 4500:1, or lies in a range of values ​​between any two of these.

[0165] In some embodiments, the mass concentration ratio of copper ions to brightening agent is optionally 300 : 1, 1000 : 1, 2000 : 1, 3000 : 1, 4000 : 1, 5000 : 1 or 6000 : 1 or lies in a range of values ​​between any two of these.

[0166] In some embodiments, the electroplating solution comprises gelatin at a concentration of 20 to 150 mg / L, polyethylene glycol at a concentration of 15 to 100 mg / L, hydroxyethylcellulose at a concentration of 10 to 80 mg / L, bis-(sodium sulfopropyl)disulfide at a concentration of 15 to 150 mg / L, copper ions at a concentration of 45 to 90 g / L and chloride ions at a concentration of 10 to 80 mg / L.

[0167] In some embodiments, the peak current density of the pulse current is denoted as I, with the unit A / dm². 2 ; the duty cycle of the pulse current is denoted as s, where the peak current density I and the duty cycle s are given by the condition 2 A / dm² 2 ≤ I × s ≤ 18 A / dm 2 fulfill.

[0168] In this document, the term "current duty cycle of a pulse current" refers to the ratio of the current flow time within a pulse cycle to the total duration of the pulse cycle.

[0169] In some embodiments, the product I × s of the peak current density I and the duty cycle s is 2 A / dm². 2 , 4 A / dm 2 , 6 A / dm 2 , 8 A / dm 2 , 10 A / dm 2 , 12 A / dm 2 , 14 A / dm 2 , 16 A / dm 2 or 18 A / dm 2 or lies within a range of values ​​between any two of them.

[0170] The product of the peak current density I and the duty cycle s corresponds to the average current density within a pulse cycle. With pulsed current deposition, the average current density within the pulse cycle can be higher than the maximum achievable current density with direct current deposition, since an excessively high direct current deposition density can lead to hydrogen evolution and concentration difference polarization in the electroplating solution, thereby reducing the uniformity of the copper foil during the electroplating process. Within the range described above, the product of the peak current density I and the duty cycle s allows for a dynamic balance between the consumption and replenishment of copper ions in the electroplating solution by controlling the switching on and off of the current.This reduces the concentration difference between the copper ion deposition area and other parts of the electroplating solution, prevents significant concentration difference polarization in the electroplating solution, and improves the uniformity of the crystal grain size in the thickness direction of the produced copper foil. Furthermore, the product of the peak current density I and the duty cycle s within the above range can control the nucleation and growth rate of the crystal grains, thereby enabling the production of small particle sizes and improving the mechanical strength of the copper foil.

[0171] In some embodiments, the peak current density I of the pulse current satisfies the condition 3.3 A / dm². 2 ≤ I ≤ 333 A / dm 2 .

[0172] In some embodiments, the peak current density I of the pulse current is 3.3 A / dm². 2 , 8.35 A / dm 2 , 10 A / dm2 , 100 A / dm 2 , 150 A / dm 2 , 167 A / dm 2 , 180 A / dm 2 , 200 A / dm 2 , 300 A / dm 2 or 333 A / dm 2 or lies within a range of values ​​between any two of them.

[0173] In some embodiments, the duty cycle s of the pulse current is 2% to 50%.

[0174] In some embodiments, the duty cycle s of the pulse current is 2%, 3.30%, 5%, 10%, 20%, 30%, 40% or 50%, or lies in a range of values ​​between any two of these.

[0175] In some embodiments, the pulse width of the pulse current is 1 ms to 50 ms.

[0176] In this document, the term "pulse width" refers to the duration of the current flow within a pulse cycle.

[0177] In some embodiments, the pulse width of the pulse current is 1 ms, 5 ms, 10 ms, 15 ms, 20 ms, 25 ms, 30 ms, 35 ms, 40 ms, 45 ms or 50 ms, or lies in a range of values ​​between any two of these.

[0178] In some embodiments, the distance between the cathode electrode and the anode electrode is 15 mm to 20 mm.

[0179] In some embodiments, the distance between the cathode electrode and the anode electrode is 15 mm, 16 mm, 17 mm, 18 mm, 19 mm or 20 mm, or lies in a range between any two of these values.

[0180] In some embodiments, the deposition temperature is 45 °C to 60 °C.

[0181] In some embodiments, the deposition temperature is optionally 45 °C, 50 °C, 55 °C or 60 °C, or lies within a range between any two of these.

[0182] In some embodiments, the cathode electrode is a titanium roller or plate.

[0183] In some embodiments, the anode electrode is a titanium substrate plate.

[0184] In some embodiments, the deposition time is greater than or equal to 80 s.

[0185] In some embodiments, the deposition time is optionally 80 s, 100 s, 200 s, 220 s, 240 s, 280 s, 300 s, 400 s, 500 s, 800 s or 1000 s, or lies in a range between any two of these.

[0186] In some embodiments, the electroplating process particularly includes the periodic application of a pulsed current to the electroplating solution to reduce and deposit copper ions in the electroplating solution, wherein the peak current density I of the pulsed current meets the condition 100 A / dm² 2 ≤ I ≤ 180 A / dm 2fulfilled, the duty cycle s of the pulse current meets the condition 2 % ≤ s ≤ 10 % and the deposition time is 80 s to 250 s.

[0187] In some embodiments, the manufacturing process is a continuous production process.

[0188] In some embodiments, the manufacturing process is a roller deposition process. Its operating principle is that the cathode roller is connected to the negative terminal of the power source and the anode container is connected to the positive terminal. When the copper-ion-containing electroplating solution enters the anode container, an electric field forms between the positive and negative terminals. Under the influence of this electric field, the copper ions migrate to the surface of the cathode roller and are deposited there. The copper foil obtained by deposition is removed from the cathode roller and wound onto another roller. The electroplating solution is continuously added and circulated. Under the influence of the electric field, the copper ions are continuously deposited on the cathode roller, continuously removed, and wound onto the winding shaft.This manufacturing process enables the continuous production of copper foil on a large scale, thus facilitating industrial applications.

[0189] The present application also provides a copper foil which has the same characteristics as the copper foil in the aforementioned current collector, which will not be discussed again here.

[0190] In any embodiment, the copper foil is produced by a manufacturing process according to any of the foregoing embodiments.

[0191] In some embodiments, the maximum width of the copper foil is greater than or equal to 1.5 meters and / or the maximum length of the copper foil is greater than or equal to 10000 meters.

[0192] In some embodiments, the maximum width of the copper foil is 1.5 meters, 2 meters, 2.5 meters, 3 meters, 3.5 meters, 4 meters, 6 meters, 8 meters or 10 meters, or lies in a range of values ​​between any two of these.

[0193] In some embodiments, the maximum length of the copper foil is 10000 meters, 15000 meters, 20000 meters, 25000 meters, 30000 meters, 60000 meters or 100000 meters, or lies in a range of values ​​between any two of these.

[0194] The copper foil provided in the embodiments of the present application can be produced in large dimensions and has prospects for industrial application. Electrode sheet

[0195] The present application further provides an electrode sheet comprising a current collector in any embodiment.

[0196] In some embodiments, the electrode sheet is a negative electrode sheet and the current collector is a negative electrode current collector.

[0197] In some embodiments, the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector. For example, the negative electrode current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is arranged on one or both of the two opposite surfaces of the negative electrode current collector.

[0198] In some embodiments, the negative electrode film layer comprises a negative electrode active material. In some embodiments, the negative electrode active material comprises, but is not limited to, one or more of conventional natural graphite, synthetic graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate. The silicon-based material may comprise one or more of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy material. The tin-based material may comprise one or more of elemental tin, tin oxide, and tin alloy.

[0199] In some embodiments, the electrode sheet is a negative electrode sheet, comprising a current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer contains an active negative electrode material, the active negative electrode material being a silicon-based material. The elongation at break of the negative electrode sheet at room temperature is greater than or equal to 2%, optionally 3% to 5%.

[0200] In this document, the term "room temperature" refers to 20 ± 10 °C.

[0201] In this document, the term "elongation at break" refers to the ratio of the change in length of a material during deformation until fracture under load to its original length. It is usually expressed as a percentage and is an important parameter for evaluating a material's ability to deform under tension during tensile testing.

[0202] The elongation at break of the negative electrode sheet can be determined using methods known in engineering. As an example, at least four samples, each 200 ± 0.5 mm long and 15 ± 0.25 mm wide, are cut from the negative electrode sheet. Using a pneumatic clamping device, the electrode sheet is guided through the upper and lower collets at an air pressure of 0.2 MPa. By actuating the pneumatic valve, the upper collet is first closed, maintaining a weak connection state (i.e., the sample remains in its natural flexural state without external forces acting upon it). Subsequently, the lower collet is closed. The sample is continuously loaded at a tensile rate of 2 mm / min until fracture, with a measuring distance of 50 mm.The elongation at break of the negative electrode sheet is determined by dividing the extension of the measuring distance of the sample material at break by the original measuring distance of the sample material before stretching.

[0203] In some embodiments, the elongation at break of the negative electrode sheet at room temperature is optionally 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%, or lies in a range between any two of these values.

[0204] In some embodiments, the thickness of the negative electrode sheet is 100 µm to 150 µm, which is measured directly with a high-precision micrometer.

[0205] The negative electrode sheet of the secondary battery has a high elongation at break, which provides sufficient expansion space during the subsequent cycle of the secondary battery and allows it to withstand the reciprocating expansion of the secondary battery during the cycle, so that the silicon-based secondary battery has a high energy density while improving safety performance and cycle life.

[0206] In some embodiments, the compaction density of the negative electrode sheet is greater than or equal to 1.5 g / cm³. 3 , and the cold pressing elongation is less than or equal to 0.1%, optionally it is 0.06% to 0.1%.

[0207] In the present application, the density of the negative electrode sheet has a meaning known in the art and can be determined using methods known in the art. The density of the negative electrode sheet = the surface density of the negative electrode film layer / the thickness of the negative electrode film layer. The thickness of the negative electrode film layer has a meaning known in the art and can be determined using methods known in the art, for example, using a high-precision micrometer (e.g., model Mitutoyo 293-100 with an accuracy of 0.1 µm). The areal density of the negative electrode film layer can be determined using methods known in the art.For example, a cold-pressed negative electrode sheet or one obtained from disassembling a battery can be used (in the case of a double-sided coated negative electrode sheet, the negative electrode film layer can first be wiped off one side). This is punched out into small circular discs with an area S1, their weight is weighed, and recorded as M1. Subsequently, the negative electrode film layer of the negative electrode sheet is wiped off, and the weight of the negative electrode current collector is weighed and recorded as M0. The surface density of the negative electrode sheet = (M1 - M0) / S1.

[0208] In some embodiments, the compaction density of the negative electrode sheet is optionally 1.5 g / cm³. 3 , 1.55 g / cm³ 3 , 1.6 g / cm³ 3 , 1.65 g / cm³ 3 , 1.7 g / cm³ 3 , 1.75 g / cm³ 3 , 1.8 g / cm³ 3 , 1.85 g / cm³ 3, 1.9 g / cm³ 3 , 1.95 g / cm³ 3 or 2.0 g / cm² 3 or lies within a range of values ​​between any two of them.

[0209] The cold pressing strain of the negative electrode sheet can be determined using methods known in engineering. For example, before cold pressing, two points are taken along the (MD) direction perpendicular to the cold pressing roller on the surface of the negative electrode sheet, and the distance L1 between them is measured. The distance L2 between the two points is then measured on the negative electrode sheet after cold pressing, and (L2 - L1) / L1 is the cold pressing strain of the negative electrode sheet. At least five different measurement points are recorded, and the average value is used as the cold pressing strain of the negative electrode sheet. It should be noted that the cold pressing strain of the negative electrode sheet can also be determined by characterizing a disassembled secondary battery. For example, the secondary battery is disassembled to obtain the negative electrode sheet.The difference between the strain at break of the current collector in the area of ​​the negative electrode film layer and the strain at break of the current collector in the uncoated area is then measured. This difference can also be used to characterize the cold-press strain of the negative electrode sheet.

[0210] In some embodiments, the cold pressing elongation of the negative electrode sheet is optionally 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09% or 0.1%, or lies in a range between any two of these values.

[0211] The negative electrode sheet of the secondary battery achieves a high compaction density and exhibits low elongation during the cold pressing process. This leaves more available space for electrode sheet expansion during the secondary battery's cycle, positively impacting the safety and cycle life of the secondary battery. Furthermore, low cold pressing elongation can reduce the risk of wrinkling of the negative electrode sheet's electrode tab during the cold pressing process and may even eliminate the need for the currently used pre-stretching process, which aims to reduce the likelihood of electrode tab wrinkling during cold pressing. This improves production efficiency.

[0212] In some embodiments, the compaction density of the negative electrode sheet is 1.5 g / cm³. 3 up to 2.0 g / cm³ 3 .

[0213] Compared to the carbon-based active material typically used in the negative electrode, the silicon-based material exhibits higher hardness and relatively poor lubricity, requiring a higher cold-pressing pressure to achieve the same compaction density. The silicon-containing negative electrode of the secondary battery offers high tensile strength and can achieve a high compaction density, further improving the energy density of the secondary battery while also enhancing its safety and lifespan.

[0214] In some embodiments, the mass fraction of the silicon-based material, relative to the total mass of the negative electrode film layer, is 5% to 100%.

[0215] In some embodiments, the mass fraction of the silicon-based material, based on the total mass of the negative electrode film layer, is optionally 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or 100%, or lies in a range between any two of these.

[0216] In some embodiments, the mass fraction of the silicon-based material, relative to the total mass of the negative electrode film layer, is 10% to 60%.

[0217] The silicon-based material in the aforementioned proportion range enables the secondary battery to have good energy density, safety and cycle stability.

[0218] In some embodiments, the thickness of the current collector is 2 to 10 µm.

[0219] In some embodiments, the thickness of the current collector is optionally 2 µm, 3 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, 9 µm, or 10 µm, or lies within a range between any two of these values. The thickness of the current collector can be determined using methods known in the art. For example, the thickness of the current collector can be measured with a thickness gauge. Alternatively, the current collector can be punched into small circular discs and weighed. The areal density of the sample is determined by dividing the sample mass by the sample surface area. The thickness of the current collector is then calculated by dividing the areal density by the density of the current collector material (for example, the density of a copper foil used as a current collector is 8.9 g / cm³). 3 The density of the current collector material can be characterized and measured using a composition tester.

[0220] In some embodiments, the negative electrode film layer optionally also includes a conductive element of the negative electrode. The present application does not specifically restrict the type of conductive element of the negative electrode. By way of example, the conductive element of the negative electrode may comprise one or more of superconducting carbon, conductive graphite, carbon black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0221] In some embodiments, the negative electrode film layer optionally also includes a negative electrode binder. The present application does not specifically restrict the type of negative electrode binder. By way of example, the negative electrode binder may comprise one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylate resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0222] In some embodiments, the negative electrode film layer optionally includes further additives. For example, these additives may include a thickening agent, such as sodium carboxymethylcellulose (CMC), PTC thermistor material, and the like.

[0223] The negative electrode film layer is typically formed by applying a negative electrode paste to the negative electrode current collector, followed by drying and cold pressing. The negative electrode paste is usually formed by dispersing and uniformly stirring the negative electrode active material, an optional conductive agent, an optional binder, and other optional excipients in a solvent. The solvent may be, but is not limited to, N-methyl-2-pyrrolidone (NMP) or deionized water.

[0224] The negative electrode sheet does not exclude further additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet described in the present application also includes a conductive primer layer (consisting, for example, of a conductive agent and a binder) arranged between the negative electrode current collector and the negative electrode film layer and applied to the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet described in the present application also includes a protective layer covering the surface of the negative electrode film layer. Secondary battery

[0225] The present application further provides a secondary battery, wherein the secondary battery is optionally designed as a battery cell, battery module or battery pack.

[0226] In some embodiments, the expansion force of the secondary battery cell is greater than or equal to 1000 kgf.

[0227] In some embodiments, the maximum expansion force of the secondary battery cell is greater than or equal to 2500 kgf.

[0228] In some embodiments, the maximum expansion force of the secondary battery cell is greater than or equal to 4000 kgf.

[0229] Here, 1 kgf refers to the gravitational force exerted on a 1-kilogram object at sea level and 45 degrees north latitude. 1 kgf is approximately equivalent to 9.8 newtons. The expansion force of the secondary battery cell is measured by pressure sensors arranged in a clamping device on both sides of the large surface of the electrode sheet of the secondary battery cell.

[0230] The current collector in the prior art tends to break under the high expansion force of the secondary battery, leading to safety accidents and limiting further improvements in the electrochemical performance of the secondary battery. The current collector provided in the embodiments of the present application exhibits both excellent tensile strength and elongation at break, making it suitable for secondary batteries with high expansion forces and contributing to a further improvement in the energy density of the secondary battery.

[0231] The present application does not specifically restrict the type of secondary battery. For example, the secondary battery may be a lithium-ion battery. Typically, the secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and the like. During the charging and discharging process of the secondary battery, the active ions migrate between the positive and negative electrode sheets for intercalation and deintercalation, and the electrolyte serves to conduct the active ions between the positive and negative electrode sheets. The present application does not specifically restrict the type of electrolyte, which may be selected according to the actual requirements. For example, the electrolyte may be selected from at least one of a solid electrolyte and one of a liquid electrolyte (i.e., an electrolyte solution).The secondary battery with electrolyte solution and some secondary batteries with solid electrolytes may also include a separator that is positioned between the positive and negative electrode sheets and serves as an insulating layer. [Positive electrode sheet]

[0232] In some embodiments, the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer arranged on at least one surface of the positive electrode current collector. For example, the positive electrode current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is arranged on one or both of the two opposite surfaces of the positive electrode current collector.

[0233] The positive electrode current collector can be a metal foil or a composite current collector. Copper foil can be used as an example of a metal foil. The composite current collector can comprise a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. For example, the metal material can include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. For example, the polymer material base layer can include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0234] The positive electrode film layer generally contains a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film layer is typically formed by applying a positive electrode paste to the positive electrode current collector, followed by drying and cold pressing. The positive electrode paste is generally formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring uniformly. The solvent may be, but is not limited to, N-methyl-2-pyrrolidone (NMP).For example, the binder for the positive electrode film layer 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. For example, the conductive material for the positive electrode film layer can include one or more of superconducting carbon, conductive graphite, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0235] The positive electrode active material can be a positive electrode active material known in technology for secondary batteries.

[0236] If the secondary battery of the present application is a lithium-ion battery, the positive electrode active material may, but is not limited to, one or more lithium-containing transition metal oxides, lithium-containing phosphates, and their respective modified compounds. Examples of the lithium-containing transition metal oxide may, but are not limited to, one or more lithium cobalt oxides, 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 lithium-containing phosphate may include, but are not limited to, one or more of lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0237] In some embodiments, to further improve the energy density of the secondary battery, the positive electrode active material for the lithium-ion battery can be one or more lithium transition metal oxides with the general formula Li a Ni b Co c M d O e A fand 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 one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A is one or more selected from N, F, S and Cl.

[0238] In some embodiments, for example, the positive electrode active material for lithium-ion batteries can be one or more of 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 O2, LiFePO4 and LiMnPO4 are included.

[0239] In the present application, the modified compounds of the above-mentioned positive electrode active materials can be those obtained by doping modification and / or surface coating modification of the positive electrode active material. [Electrolyte]

[0240] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0241] The types of electrolyte salt are not subject to any particular restrictions and can be selected according to the actual requirements.

[0242] If the secondary battery of the present application is a lithium-ion battery, the electrolyte salt may, for example, comprise 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 difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0243] The type of solvent is not subject to any particular restrictions and can be selected according to the actual requirements. In some embodiments, the solvent may, for example, 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), butylene 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), sulfolan (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0244] In some embodiments, the electrolyte solution optionally includes an additive. For example, the additive may include a film-forming additive for the negative electrode, a film-forming additive for the positive electrode, or an additive that can improve certain properties of the secondary battery, such as an additive to improve the overcharging behavior of the secondary battery, an additive to improve the high-temperature properties of the secondary battery, and an additive to improve the low-temperature performance of the secondary battery, etc. [Separator]

[0245] The present application does not impose any special restrictions on the type of separator, and any known separator with good chemical and mechanical stability and a porous structure may be used.

[0246] In some embodiments, the separator material can comprise one or more of glass fibers, nonwoven fabrics, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film. If the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0247] In some embodiments, the positive electrode sheet, the separator and the negative electrode sheet can be formed into an electrode arrangement by a winding process and / or a stacking process.

[0248] In some embodiments, the secondary battery may include an outer casing. This outer casing may be used to encapsulate the aforementioned electrode arrangement and the electrolyte.

[0249] In some embodiments, the outer packaging of the secondary battery can be a rigid casing, for example, a hard plastic casing, an aluminum casing, a steel casing, etc. The outer packaging can also be a soft casing, for example, a bag-like soft casing. The material of the soft casing can be plastic, for example, one or more types of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0250] The present application does not impose any special restrictions regarding the shape of the secondary battery; it may be cylindrical, rectangular, or any other shape. For example, shows Fig. 5 a secondary battery 5 with a square structure as an example.

[0251] In some embodiments, such as in Fig.As shown in Figure 6, the outer packaging can comprise a housing body 51 and a cover plate 53. The housing body 51 can include a base plate and a side plate connected to the base plate, the base plate and the side plate forming a receiving chamber. The housing body 51 has an opening that communicates with the receiving chamber, and the cover plate 53 serves to cover the opening to close the receiving chamber. The positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is encapsulated in the receiving chamber. The electrolyte solution is saturated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more and can be adjusted as required.

[0252] The manufacturing process for the secondary battery in the present application is known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte solution can be assembled to form a secondary battery. For example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly by a winding or stacking process. The electrode assembly is inserted into an outer packaging. After drying, an electrolyte solution is injected, and after vacuum sealing, standing, formation, and calibration, a secondary battery is obtained.

[0253] In some embodiments of the present application, the secondary batteries according to the present application can be assembled into a battery module. The battery module can contain several secondary batteries, the exact number of which can be adapted depending on the application and capacity of the battery module.

[0254] Fig. Figure 7 shows a schematic representation of a battery module 4 as an example. As in Fig. As shown in Figure 7, several secondary batteries 5 can be arranged one behind the other along the length of the battery module 4. Of course, other arrangements are also possible. Furthermore, the multiple secondary batteries 5 can be secured by fastening elements.

[0255] Optionally, the battery module 4 can also include a housing with a receiving space, in which the multiple secondary batteries 5 are received.

[0256] In some embodiments, the aforementioned battery modules can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be adjusted depending on the application and the battery pack's capacity.

[0257] The Fig. 8 and Fig. Figure 9 shows a battery pack 1 as an example. As shown in the Fig. 8 and Fig. As shown in Figure 9, the battery pack 1 can comprise a battery box and several battery modules 4 arranged within the battery box. The battery box comprises an upper box body 2 and a lower box body 3; the upper box body 2 can cover the lower box body 3 and form an enclosed space for the battery modules 4. The multiple battery modules 4 can be arranged within the battery box in any configuration. Power-consuming device

[0258] The present application further provides a power-consuming device comprising at least one of the secondary battery, battery module, and battery pack provided by the present application. The secondary battery, battery module, or battery pack can be used as a power source for the power-consuming device or as an energy storage device for the power-consuming device. The power-consuming device can be, but is not limited to, a mobile device (such as a mobile phone, laptop, etc.), an electric vehicle (such as a pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0259] Depending on its usage requirements, the secondary battery, battery module or battery pack can be selected as the power-consuming device.

[0260] Fig. Figure 10 shows a schematic representation of a power-consuming device as an example. The power-consuming device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the power-consuming device's requirements for high power and high energy density, a battery pack or battery module can be used.

[0261] Another example of a power-consuming device could be a mobile phone, tablet, laptop, etc. The power-consuming device typically needs to be lightweight and thin and can use a secondary battery as a power source. Example of implementation

[0262] The following embodiments describe in more detail the content disclosed in the present application. These embodiments serve only as an illustration, since various modifications and changes within the scope of the content disclosed in the present application are obvious to the person skilled in the art. Unless otherwise stated, all proportions, percentages, and ratios given in the following embodiments refer to mass. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further treatment. The instruments used in the embodiments are commercially available. Example 1(1) Production of the copper foil

[0263] A copper plate or wire with a purity above 99.9% was dissolved in a sulfuric acid solution to prepare a copper sulfate pentahydrate solution as the copper source. At 60 °C, an additive and oxalic acid were added to prepare an electroplating solution, the additive comprising gelatin, polyethylene glycol, hydroxyethylcellulose, and sodium chloride. The pH of the electroplating solution was 3.5, and the concentrations of the individual components were as follows: copper ion concentration 45 g / L, gelatin concentration 90 mg / L, polyethylene glycol concentration 50 mg / L, hydroxyethylcellulose concentration 30 mg / L, chloride ion concentration 80 mg / L, bis(sodium sulfopropyl) disulfide concentration 75 mg / L, and the remainder was deionized water.

[0264] A current with a rectangular pulse current shape was periodically applied to a polished titanium cathode roller. The titanium roller was immersed in the electroplating solution. The surface area of ​​the titanium roller was 0.3 dm². 2 The rotational speed of the titanium roller was 2 m / min. The impulse current was measured at a current density of 167 A / dm². 2 A duty cycle of 5% and a pulse width of 1 ms were applied. The distance between the cathode and anode was 20 mm. The deposition temperature was 60 °C. The electroplating time was 224 s, and a copper foil with a thickness of 6 µm was deposited on the titanium roller. (2) Battery production

[0265] LiNi were 0,8 Co 0,1 Mn 0,1O2 (NCM811) as a positive electrode active material, acetylene carbon black as a conductive agent, and polyvinylidene fluoride (PVDF) as a binder were dissolved and uniformly stirred and mixed in the solvent N-methyl-2-pyrrolidone (NMP) in a weight ratio of 90:5:5 to obtain a positive electrode paste; then, a positive electrode current collector was uniformly coated with the positive electrode paste, and after drying, cold pressing, and cutting, a positive electrode sheet was obtained.

[0266] Artificial graphite (as the negative electrode active material), carbon black (as the conductive agent), styrene-butadiene rubber (SBR) (as the binder), and sodium carboxymethylcellulose (CMC) (as the thickener) were dissolved and uniformly mixed in deionized water in a weight ratio of 90:4:4:2 to produce a negative electrode paste. The copper foil of the negative electrode current collector was then uniformly coated with the negative electrode paste once or several times. After drying, a negative electrode layer was obtained, which was processed into a negative electrode sheet by cold pressing and cutting.

[0267] In a glovebox under an argon atmosphere (H₂O < 0.1 ppm, O₂ < 0.1 ppm), the organic solvents fluoroethylene carbonate (FEC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) were mixed uniformly in a mass ratio of 1:2:7. Subsequently, lithium salt LiPF₆ was added at a concentration of 12.5 wt% to dissolve it in the organic solvents. Then, 2.0 wt% fluoroethylene carbonate, 0.5 wt% 1,3-propanesultone, and 0.5 wt% succinic anhydride were added as additives to the organic solvent and mixed and stirred uniformly to obtain an electrolyte solution. A polypropylene film was used as a separator.

[0268] The positive electrode sheet, the separator, and the negative electrode sheet were stacked sequentially, with the separator positioned between the positive and negative electrode sheets to provide insulation, and an electrode assembly was produced by a winding process; the electrode assembly was placed in a battery casing, after drying the electrolyte solution was injected, and a lithium-ion battery was produced by formation, standing, etc. Exemplary embodiments 2 to 8

[0269] The manufacturing processes of embodiments 2 to 8 were basically the same as that of embodiment 1, with the difference that the components or concentrations of the electrolyte solution or the parameters of the pulse current deposition were changed, as specifically shown in Table 1. Example 9

[0270] The manufacturing process of embodiment 9 was fundamentally the same as that of embodiment 1, with the exception that the mixing ratio of the negative electrode sheet was changed. Specifically: Silicon carbon (with a silicon content of 20 wt.% to 50 wt.%) and synthetic graphite, carbon black as a conductive agent, styrene-butadiene rubber (SBR) as a binder, and sodium carboxymethylcellulose (CMC) as a thickener were dissolved and uniformly mixed in deionized water in a mass ratio of 10:86:1:1.5:1.5 to produce a negative electrode paste; then the copper foil of the negative electrode current collector was uniformly coated with the negative electrode paste once or several times. After drying, a negative electrode layer was obtained, which was processed into a negative electrode sheet by cold pressing and cutting. Example 10

[0271] Exemplary embodiment 10 was essentially the same as exemplary embodiment 9, with the difference that the components in the negative electrode film layer remained unchanged and the ratio of the components in the negative electrode film layer was adjusted. Specifically, the ratio of silicon-carbon and synthetic graphite as the negative electrode active material, acetylene carbon black as the conductive agent, styrene-butadiene rubber (SBR) as the binder, and sodium carboxymethylcellulose (CMC) as the thickening agent in the negative electrode film layer was 30 : 66 : 1 : 1.5 : 1.5. Example 11

[0272] Exemplary embodiment 11 was basically the same as exemplary embodiment 10, with the difference that the compaction density of the film layer of the negative electrode sheet was adjusted as specifically shown in Table 4. Comparative example 1

[0273] The manufacturing process of comparative example 1 was basically the same as that of embodiment 1, with the difference that the electroplating process was changed, using a direct current with a deposition current density of 8.35 A / dm². 2 used for deposition, as specifically shown in Table 1. Comparative example 2

[0274] The manufacturing process of comparative example 2 was essentially the same as that of embodiment 9, with the difference that a conventional copper foil with a thickness of 6 µm was used as the current collector. Under test conditions of room temperature, a sample thickness of 6 ± 0.2 µm and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil was 350 MPa and the elongation at break was 6.2%. Comparative example 3

[0275] The manufacturing process of Comparative Example 3 was essentially the same as that of Comparative Example 2, with the difference that a pre-stretching process was carried out before cold pressing in the production of the negative electrode sheet. Specifically, a pre-stretching roller with a tensile force of 400 N to 700 N was added before cold pressing to pre-stretch the uncoated area of ​​the coated copper foil. This prevented the coated area from being stretched while the uncoated area remained unstretched during cold pressing, which would lead to wrinkling. Table 1 Serial number Electroplating solution Impulse current Copper ions (g / L) Leveling agent (mg / L) Wetting agent (mg / L) Chloride ions (mg / L) Brightener bis-(sodium sulfopropyl) disulfide (mg / L) Peak current density (A / dm²) Duty cycle Peak current density × duty cycle (A / d) m 2 ) Polyethylene glycol Hydroxyethylcellulose Example 1 45 90 50 30 80 75 167 5% 8,35 Example 2 45 120 100 60 80 150 167 5% 8,35 Example 3 45 90 50 30 80 75 180 2% 3,6 Example 4 45 90 50 30 80 75 150 2% 3 Example 5 45 90 50 30 80 75 180 10% 18 Example 6 45 90 50 30 80 75 100 2% 2 Example 7 90 20 15 12 30 15 167 3,30% 5,511 Example 8 300 90 50 30 80 1 167 5% 8,35 Comparative example 1 45 90 50 30 80 75 Direct current 8.35 A / dm 2 Performance tests(1) Thickness test

[0276] A sample measuring 20 × 15 cm was taken. 2The thickness of the sample was calculated using the weight method as follows: A cut-out sample strip was weighed on an electronic balance to determine its weight. The volume of the sample strip was then calculated based on the density ρ of the copper foil, which is 8.96 g / cm³. 3 calculated. Since the length and width of the test strip are known, its thickness can be derived from them. (2) Testing of mechanical properties

[0277] In accordance with standard GB / T 5230-1995 "Electrolytic copper foil", a tensile test specimen with a length L0 of 200 mm and a width of 15 mm was cut. The specimen was weighed on a scale, and the mass was recorded in m. A tensile strength test was carried out using a universal testing machine at 25 °C and a tensile speed of 50 mm / min.

[0278] Then the cross-sectional area S0 of the Tensile test=mρ×L0, where ρ is 8.96 g / cm³3 was, m was given in grams and L0 in centimeters.

[0279] The specimen was continuously loaded until it broke. The maximum load F was read either from the force gauge or from the tensile force-strain curve. The tensile strength σ b was calculated according to Formula I. σb=FS0

[0280] The distance between the two lines after the specimen fracture was designated L1, which was measured on the specimen or read from the tensile force-strain curve. L1 can be determined using a straight line method or the displacement method, and the elongation at break δ was calculated according to Formula II. δ=L1−L0L0 (3) Examination of the characteristics of the crystal grains of the copper foil

[0281] Using a combination of electron backscatter diffraction (EBSD) and scanning electron microscopy, the cross-section of the copper foil was observed, with the Oxford C-Nano+ being the electron backscatter diffraction instrument. This allowed for the creation of an inverse pole-figure distribution plot, and the particle size of the individual crystal grains was measured. The diameter of the equivalent circle of the crystal grains was used as the particle size, and a distribution statistic of the crystal grain sizes was performed. A skew distribution was used for fitting, and the particle size corresponding to the peak value was used as the average particle size of the crystal grains in the copper foil.The number of twins was statistically determined using the inverse pole figure, where different colors represent different crystal grain orientations and red lines within the crystal grains represent twin boundaries, indicating twin structures. The fraction of nanotwins was statistically determined using analysis software belonging to the Oxford C-Nano+ electron backscatter diffraction instrument. A similar method was used to measure the fraction of coaxial or quasi-coaxial crystal grains. (4) Testing of maximum surface roughness

[0282] The surface of the copper foil was wiped with alcohol, placed securely on a horizontal surface, and the stylus was positioned on the foil. The stylus tip was brought into contact with the foil and carefully drawn across the surface. The roughness of the copper foil was determined by reading the measuring device. The test was performed five times at different points on the copper foil, and the highest reading was considered the maximum surface roughness of the copper foil. (5) State of Health (SOH) corresponding to crack failure

[0283] At 25 °C, the battery was charged to a voltage of 3.8 V with a constant current of 1 C, then charged to a current ≤ 0.05 C with a constant voltage of 3.8 V, and subsequently discharged to a voltage of 2.5 V with a constant current of 1 C – this constitutes a charge and discharge cycle. The charge and discharge cycle was repeated. Subsequently, computed tomography (CT) was used to determine whether internal cracks had formed in the battery. If cracks were present, the battery, which had failed after cracking occurred during the cycle, was disassembled, the negative electrode sheet was removed, and samples were taken from the crack-free areas. The elongation at break of the sample was measured according to the elongation at break method described above, and the state of health (SOH) of the battery at this time point was determined by simulation. (6) Cycle simulation calculation:

[0284] Based on finite element analysis, a fracture model was created, using a wound core after hot pressing (JR) to model the battery cell. The tensile force-strain curve of the electrode sheet was then input as a mechanical parameter. Finally, the individual cell's expansion force data were used to calibrate the free springback of the JR dimensions, which serves as input for the cracking model. The criterion is that the electrode sheet strain of the individual cell under expansion force is greater than the fracture strain of the electrode sheet. This allowed for the simulation and analysis of the corresponding state of charge (SOH) at the moment of electrode sheet fracture during long-cycle operation. (7) Observation of the electrode tab area after cold pressing:

[0285] If wrinkles appear in the uncoated area of ​​the electrode sheet, it was determined that the electrode flap is creased; if the uncoated area of ​​the electrode sheet remains smooth and shows no abnormal phenomena, it was determined that the electrode flap is not creased. Test results Table 2 Serial number copper foil battery Average particle size of the crystal grains (nm) Proportion of the number of twins Tensile strength (MPa) Elongation at break SOH value, which corresponds to crack failure Example 1 200 85,00 % 922 5,27% 48% SOH Example 2 213 80,50 % 856 5,50 % 55% SOH Example 3 133 88,00 % 996 6,00 % 43% SOH Example 4 207 82,60 % 910 5,00 % 52% SOH Example 5 234 79,00 % 790 5,10% 59% SOH Example 6 200 80,60 % 880 5,00 % 57% SOH Example 7 200 85,00 % 812 5,07 % 58% SOH Comparative example 1 809 56,00 % 360 5,00 % 75% SOH Table 3 Serial number copper foil battery Average particle size of the crystal grains (nm) Proportion of the number of twins Maximum surface roughness (µm) Tensile strength (MPa) Elongation at break SOH value, which corresponds to crack failure Example 1 200 85,00 % 0,12 922 5,27% 48% SOH Example 8 275 58,00 % 0,25 659 4,06 % 63% SOH

[0286] The test results of the exemplary implementations and comparison examples are listed in Tables 1 to 3.

[0287] From the comparison between the embodiments and the comparative examples, it is evident that the average particle size of the crystal grains in the copper foil provided in the present application is 50 nm to 400 nm and that, based on the total number of crystal grains in the copper foil, the proportion of twins is greater than or equal to 60%, which results in excellent tensile strength and elongation at break, can reduce the state of charge (SOH) value corresponding to crack failure of the battery, and contributes to improving the safety and cycle life of the battery.

[0288] Fig. Figure 1 is a schematic diagram of the particle size distribution of the crystal grains of the copper foil from embodiment 1; Fig. Figure 2 is an inverse pole figure distribution diagram of the electron backscatter diffraction pattern of the copper foil from embodiment 1; and Fig.Figure 3 is a diagram of the tensile force-strain curve of the copper foil from embodiment 1. From the combination of the Fig. 1 and Fig. Figure 2 shows that the average particle size of the crystal grains in the copper foil from embodiment 1 is 200 nm; the minimum particle size of the crystal grains is about 10 nm; based on the total number of crystal grains in the copper foil, the proportion of the number of crystal grains with a particle size below 200 nm is 34%, the proportion of the number of crystal grains with a particle size between 200 and 500 nm is about 65%, and the proportion of the number of crystal grains with a particle size above 500 nm is not more than 2%; and the maximum surface roughness of the copper foil is 0.12 µm. Fig.Figure 4a is an X-ray diffraction diagram of the copper foil from embodiment 2; wherein the crystal plane diffraction intensity of the (111) texture in the copper foil is 80.06% of the total crystal plane diffraction intensity of the (111) texture, (200) texture, (220) texture, (311) texture, and (222) texture in the copper foil. Compared to the copper foil from comparative example 1 in Fig. 4b the proportion of the crystal plane diffraction intensity of the (111) texture in the copper foil to the total crystal plane diffraction intensity of the (111) texture, (200) texture, (220) texture, (311) texture and (222) texture in the copper foil is significantly increased.

[0289] As can be seen from Table 3, the maximum surface roughness of the copper foil can be reduced and at the same time the tensile strength and elongation at break of the copper foil can be further improved if the additive in the electroplating solution also contains a certain amount of leveling agent, wetting agent and brightening agent.

[0290] From the comparison of embodiments 1, 2 and 8, it can be seen that, in comparison to the electroplating solution with high copper ion concentration and low additive concentration, the electroplating solution with low copper ion concentration and high additive concentration can further improve the tensile strength and elongation at break of the copper foil.

[0291] From the comparison of embodiments 1, 4 and 6 with embodiment 5, it can be seen that the product of high peak current density and duty cycle leads to an increase in the average particle size of the crystal grains of the copper foil and a reduction in the mechanical properties, but the values ​​are nevertheless superior to those of comparative example 1. Table 4 Serial number Mass fraction of silicon-based material Whether to advance before cold pressing Compaction density g / cm³ 3 Elongation at break of the electrode sheet The SOH value calculated by simulation corresponds to the fracture of the electrode sheet. Maximum expansion force (N) of the secondary battery cell Cold pressing of the electrode blade Is the electrode tab crumpled? Example 9 10% No 1,5 3,4% 22.3% SOH 41200 0,06 % No Example 10 30% No 1,5 3,1 % 44.6% SOH 37400 0,08 % No Example 11 30% No 1,75 2,8% 58.2% SOH 29500 0,10 % No Comparative example 2 / No / / / / / Yes Comparative example 3 10% Yes 1,5 1,9% 73.2% SOH 15600 0,32 % No

[0292] From a comparison of embodiments 9 to 11 with comparative example 3, it can be seen that the secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer arranged on at least one side of the negative electrode current collector, wherein the negative electrode film layer contains a negative electrode active material, the negative electrode active material being a silicon-based material. An elongation at break of the negative electrode sheet at room temperature of greater than or equal to 2% can reduce the SOH value corresponding to the failure of the cell's electrode sheet and thereby increase the battery's lifetime.

[0293] A comparison of embodiments 9 to 11 with comparative example 2 shows that, by using the current collector in these embodiments in a secondary battery with silicon-based material, no wrinkling occurs in the electrode tab during the production of the negative electrode sheet, even without a pre-stretching process. This optimizes the battery manufacturing step and increases production efficiency.

[0294] It should be noted that the present application is not limited to the embodiments mentioned above. The above embodiments are merely examples, and all embodiments that exhibit essentially the same structure and effect as the technical idea within the technical solution of the present application are included within its scope. Furthermore, other possibilities, in which various modifications conceivable to a person skilled in the art are added to the embodiments and some components of the embodiments are combined to form other embodiments, are also included within the scope of the present application without departing from the core of the present application. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] Standard GB / T 5230-1995 [0130, 0277]

Claims

[1] Current collector, characterized by , that the current collector comprises a copper foil, wherein the average particle size of the crystal grains in the copper foil is 50 nm to 400 nm and the proportion of the number of nanotwins, based on the total number of crystal grains in the copper foil, is greater than or equal to 60%. [2] Current collector according to claim 1, characterized by that the crystal grains in the copper foil exhibit one or more of the following characteristics: (1) The average particle size of the crystal grains in the copper foil is 50 nm to 300 nm; (2) In relation to the total number of crystal grains in the copper foil, the proportion of crystal grains with a particle size of less than 200 nm is 20% to 40%, and the proportion of crystal grains with a particle size between 200 nm and 500 nm is 50% to 80%; (3) In relation to the total number of crystal grains in the copper foil, the proportion of the number of crystal grains with a particle size greater than 500 nm is less than or equal to 5%; (4) With respect to the total number of crystal grains in the copper foil, the proportion of the number of coaxial or quasi-coaxial crystal grains is greater than or equal to 80%, wherein the length ratio a1 of the principal axis to the minor axis of the coaxial or quasi-coaxial crystal grains satisfies the condition 1 ≤ a1 < 2; (5) In relation to the total number of crystal grains in the copper foil, the proportion of the number of columnar crystal grains is less than 10%, wherein the length ratio a2 of the principal axis to the minor axis of the columnar crystal grains satisfies the condition a2 > 2; (6) The ratio of the crystal plane diffraction intensity of the (111) texture in the copper foil to the total crystal plane diffraction intensity of the (111) texture, (200) texture, (220) texture, (311) texture and (222) texture in the copper foil is 60% to 85%; (7) The copper foil has a first and a second surface arranged opposite each other, the thickness of the copper foil being referred to as H, the area from the first surface of the copper foil to the thickness range of 0.2 H to 0.5 H being referred to as the first area of ​​the copper foil and the area from the second surface of the copper foil to the thickness range of 0.2 H to 0.5 H being referred to as the second area of ​​the copper foil, wherein the absolute value of the difference between the average particle size of the crystal grains in the first area and the average particle size of the crystal grains in the second area is less than or equal to 150 nm; (8) The proportion of nanotwins in the copper foil is 65% to 90% of the total number of crystal grains. [3] Current collector according to claim 1 or 2, characterized by that the copper foil has one or more of the following characteristics: (1) The maximum surface roughness of the copper foil is less than or equal to 3 µm; (2) The thickness H of the copper foil satisfies the condition 3 µm ≤ H ≤ 15 µm; (3) Under test conditions of room temperature, a sample thickness of 6 ± 0.2 µm and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is greater than or equal to 600 MPa and the elongation at break of the copper foil is greater than or equal to 4%; (4) Under test conditions of room temperature, a sample thickness of 6 ± 0.2 µm and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is 700 MPa to 1500 MPa; the elongation at break of the copper foil is 4.5% to 10%. [4] Electrode sheet, characterized by that the electrode sheet comprises a current collector according to one of claims 1 to 3. [5] Secondary battery, characterized by that it comprises an electrode sheet according to claim 4. [6] Secondary battery according to claim 5, characterized by that the maximum expansion force of the secondary battery cell is greater than or equal to 1000 kgf. [7] Secondary battery according to claim 5, characterized by that the maximum expansion force of the secondary battery cell is greater than or equal to 2500 kgf. [8] Secondary battery according to claim 5, characterized by that the maximum expansion force of the secondary battery cell is greater than or equal to 4000 kgf. [9] Secondary battery according to any one of claims 5 to 8, characterized by, that the electrode sheet is a negative electrode sheet, wherein the negative electrode sheet comprises the current collector and a negative electrode film layer arranged on at least one side of the current collector, wherein the negative electrode film layer contains a negative electrode active material, wherein the negative electrode active material contains a silicon-based material, and the elongation at break of the negative electrode sheet at room temperature is greater than or equal to 2%. [10] Secondary battery according to claim 9, characterized by , that the elongation at break of the negative electrode sheet at room temperature is 3% to 5%. [11] Secondary battery according to claim 9, characterized by that the compaction density of the negative electrode sheet is greater than or equal to 1.5 g / cm³ 3 is and the cold pressing elongation of the negative electrode sheet is less than or equal to 0.1%. [12] Secondary battery according to claim 11, characterized by, that the cold pressing elongation of the negative electrode sheet is 0.06% to 0.1%. [13] Secondary battery according to claim 9 or 10, characterized by , that the compaction density of the negative electrode sheet is 1.5 g / cm³ 3 up to 2.0 g / cm³ 3 amounts. [14] Secondary battery according to any one of claims 9 to 13, characterized by , that the mass fraction of the silicon-based material, relative to the total mass of the negative electrode film layer, is 5% to 100%. [15] Secondary battery according to any one of claims 9 to 14, characterized by , that the mass fraction of the silicon-based material, relative to the total mass of the negative electrode film layer, is 10% to 60%. [16] Secondary battery according to any one of claims 9 to 15, characterized by , that the thickness of the current collector is 2 µm to 10 µm. [17] Power-consuming device, characterized bythat it comprises a secondary battery according to any one of claims 5 to 16.

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