Secondary battery and power-consuming device

Abstract

Secondary battery, characterized in that it comprises a copper foil, wherein the copper foil comprises copper crystal grains of different particle sizes, wherein the copper crystal grains comprise copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5% to 30%.

Description

Cross-references

[0001] The present application refers to Chinese patent application No. 202411154807.0, entitled “Secondary battery, its manufacturing process and power-consuming device”, filed on August 21, 2024, which is hereby incorporated by reference in its entirety. Technical field

[0002] The present application relates to the technical field of secondary batteries and in particular to a secondary battery and a power-consuming device. State of the art

[0003] With the widespread use of secondary batteries in energy storage systems for hydroelectric, coal, wind and solar power plants, as well as in many different areas such as electric hand tools, electric bicycles, electric motorcycles, electric vehicles, military equipment and aerospace, the market is placing ever higher demands on the energy density of secondary batteries.

[0004] Energy density can be improved by using silicon-based negative electrode active materials or by increasing the amount of secondary battery active materials. However, silicon-based materials have a high coefficient of thermal expansion, causing silicon-based batteries to expand significantly when heated; and with an increasing amount of secondary battery active materials, the cell volume also increases. Both of these factors place higher demands on the properties of the negative electrode current collector. The copper foil of the negative electrode current collector is a crucial component of secondary batteries. It can inhibit cell expansion and prevent the anode of the secondary batteries from breaking during use, thus significantly influencing the electrical properties and safety performance of the secondary batteries.

[0005] Therefore, there is an urgent need for a secondary battery with a negative electrode current collector with improved properties. Disclosure of the invention

[0006] The present application provides a secondary battery wherein the secondary battery has a negative electrode current collector with improved strain properties, which effectively inhibits the expansion problem of the cell, delays or reduces the breakage of the electrode sheet and extends the service life of the secondary battery.

[0007] In a first aspect, the present application provides a secondary battery, wherein the secondary battery comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, the negative electrode current collector comprising a copper foil, the copper foil comprising copper crystal grains of different particle sizes, the copper crystal grains comprising copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm in the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm represents 5% to 30% of the total number of copper crystal grains.

[0008] The copper foil provided by the present application exhibits excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity, and providing a material basis for improving the energy density, capacity and safety of the secondary battery.

[0009] In any embodiment, the expansion force of the secondary battery is greater than or equal to 1000 kgf, and the secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, wherein the negative electrode current collector comprises a copper foil, wherein the copper foil comprises copper crystal grains of different particle sizes, wherein the copper crystal grains comprise copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm in the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm represents 5% to 30% of the total number of copper crystal grains.

[0010] During the charging and discharging cycle of a secondary battery, the intercalation / deintercalation of active ions leads to a volume expansion of the electrode sheet, particularly in batteries with a self-generated negative electrode or with newer silicon-based or lithium-metal negative electrodes. To increase the energy density of individual cells, cells with a high group span or large dimensions are developed. These factors combine to result in an overall greater expansion of the secondary battery.However, the high-expansion copper foil current collector of the secondary battery is subjected to considerable stretching and stress compression during operation, which increases the likelihood of fractures or cracks in the copper foil current collector and impairs the safety and service life of the battery cell; for this purpose, the secondary battery provided by the present application uses copper foil comprising the aforementioned copper crystal grains of different particle sizes.It exhibits excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity, and reducing the likelihood of fractures or cracks in the copper foil current collector in a high-expansion system, which has a positive effect on extending the service life of the secondary battery until cracks and failures of the electrode sheet occur and on further improving the safety and service life of the secondary battery.

[0011] In any embodiment, the thickness expansion rate of the secondary battery is 4% to 10%.

[0012] In any embodiment, the secondary battery is a wound secondary battery and the expansion force of the secondary battery is greater than or equal to 1000 kgf;The wound secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, wherein the negative electrode current collector comprises a copper foil, the copper foil comprising copper crystal grains of different particle sizes, wherein the copper crystal grains comprise copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5% to 30%.

[0013] The current collector of the negative electrode sheet in a wound secondary battery is prone to cracking at the corners. This occurs because the cell is subjected to pressure and deformation after winding, which can easily lead to irreversible damage to the current collector. This significantly increases the likelihood of cracks or fractures forming in the outer corner and inner bending areas of the negative electrode sheet after being subjected to expansion stress caused by factors such as increased internal pressure and volume expansion of the secondary battery. This increases the risk of cell failure and reduces the lifespan and safety of the secondary battery.In the wound secondary battery provided by the present application, the copper foil utilizes copper crystal grains of varying particle sizes, as described above. This significantly improves the tensile strength and elongation at break of the copper foil, resulting in excellent mechanical properties and plasticity. This reduces the likelihood of cracks or fractures forming in the copper foil under expansion stress and the probability of fractures in the electrode sheet of the wound cell. Consequently, it positively extends the service life of the secondary battery before cracks and electrode sheet failures occur, further enhancing the safety and lifespan of the secondary battery.

[0014] In any embodiment, the thickness expansion rate of the wound secondary battery is 4% to 10%.

[0015] In any embodiment, the secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, wherein the negative electrode current collector comprises a copper foil, the copper foil comprising copper crystal grains of different particle sizes, wherein the copper crystal grains comprise copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5% to 30%;and wherein the capacity per gram of the negative electrode active material in the negative electrode film layer is 800 mAh / g to 1500 mAh / g.

[0016] Increasing the amount of active materials is one of the effective measures to improve the energy density or capacity of the secondary battery, but leads to an increase in the cell volume; the applicants have found that by using the negative electrode active material with high capacity per gram, the available lithiation capacity of the negative electrode active material can be significantly increased, thus increasing the energy density or capacity of the secondary battery while minimizing the impact on the cell volume.However, the negative electrode active material with high capacity per gram exhibits greater particle volume expansion before and after lithium ion intercalation / deintercalation. This expansion stress acts on the copper foil of the electrode current collector, increasing the likelihood of the copper foil fracturing or tearing along its thickness under the expansion stress, thus reducing the safety and lifespan of the secondary battery. The secondary battery provided by the present application utilizes a copper foil comprising the aforementioned copper crystal grains of varying particle sizes. This foil exhibits excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity. This enhances the energy density and capacity of the secondary battery and simultaneously increases its safety.

[0017] In any embodiment, the capacity per gram of the negative electrode active material in the negative electrode film layer is 800 mAh / g to 1500 mAh / g.

[0018] The copper foil provided by the present application is suitable for the secondary battery, which comprises a negative electrode active material with a capacity per gram in the range of 800 mAh / g to 1500 mAh / g. Higher capacity per gram negative electrode materials (such as silicon-based negative electrodes, alkali metal negative electrodes, etc.) can intercalate more active ions, so they typically exhibit high extensibility, which increases the likelihood of the copper foil breaking or tearing in the cell. However, the copper foil according to the present application simultaneously possesses excellent mechanical properties and plasticity, which can reduce the risk of the copper foil breaking or tearing in a high-energy-density or high-extensibility battery system and improve the energy density, capacity, and safety of the secondary battery.

[0019] In any embodiment, the particle size range of the copper crystal grains is greater than 0.5 µm and less than or equal to 3 µm, which allows the tensile strength of the copper foil to be adjusted or optimized.

[0020] In any embodiment, the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm and less than or equal to 3 µm, based on the total number of copper crystal grains, is 5% to 30%.

[0021] As mentioned above, the particle size of the copper crystal grains in the range of greater than 0.5 µm and less than or equal to 3 µm can help to reduce the average particle size of the copper foil and further improve the mechanical strength of the copper foil; by further controlling the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm and less than or equal to 3 µm to 5% to 30%, the copper foil can exhibit good elongation at break and both excellent mechanical properties and plasticity, which can reduce the risk of the copper foil breaking or tearing in a high-energy-density battery system or in a high-expansion battery system, thus enabling a simultaneous increase in the energy density and safety of the secondary battery.

[0022] In any embodiment, the short diameter of at least a part of the copper crystal grains with a particle size greater than 0.5 µm is arranged along the thickness direction of the current collector.

[0023] The short diameter of at least some of the copper crystal grains with a particle size greater than 0.5 µm is oriented along the thickness direction of the current collector, indicating that the tortuosity of the crystal grain boundary pattern within the copper foil is high and that the energy required to fracture the copper foil along the crystal grain boundaries (i.e., along the thickness direction of the current collector) is higher. This helps to reduce the probability of fractures of the copper foil along the thickness direction, increases the brittleness of the current collector, and further reduces the risk of fractures or cracks in the copper foil, thereby improving the safety of the secondary battery.

[0024] In any embodiment, the proportion of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 80% to 95%, which helps to further increase the tensile strength and improve the mechanical strength of the copper foil.

[0025] In any embodiment, the proportion of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5% to 20%, which helps to further increase the elongation at break and improve the plasticity of the copper foil.

[0026] In any embodiment, the copper foil satisfies at least one of the following conditions: (1) The average particle size of the copper crystal grains is 0.3 µm to 1.2 µm; (2) The maximum particle size of the copper crystal grains is 1 µm to 2.5 µm; (3) The minimum particle size of the copper crystal grains is 0.1 µm to 0.3 µm; (4) The particle size range of the copper crystal grains is 0.8 µm to 2.5 µm.

[0027] The particle size distribution of the copper crystal grains helps to adjust the proportions of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm and the number of copper crystal grains with a particle size greater than 0.5 µm, thereby adjusting and improving the tensile strength and elongation at break of the copper foil, so that the copper foil has both excellent mechanical and plastic properties.

[0028] In any embodiment, the copper foil satisfies at least one of the following conditions: (1) The average particle size of the copper crystal grains is 0.3 µm to 0.6 µm; (2) The maximum particle size of the copper crystal grains is 1.2 µm to 2.0 µm; (3) The minimum particle size of the copper crystal grains is 0.1 µm to 0.3 µm; (4) The particle size range of the copper crystal grains is 1 µm to 2 µm.

[0029] The particle size distribution of the copper crystal grains helps to further adjust the tensile strength and elongation at break of the copper foil and to improve the mechanical and plastic properties.

[0030] In any embodiment, under test conditions of room temperature (20 ± 10°C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is 600 MPa to 1000 MPa and / or the elongation at break of the copper foil is 4% to 8%.

[0031] The copper foil exhibits excellent tensile strength and elongation at break, as well as good mechanical and plastic properties, making it suitable for high energy density or high expansion batteries, and contributing to the improvement of secondary battery safety.

[0032] In any embodiment, under test conditions of room temperature (20 ± 10°C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is 700 MPa to 1000 MPa and / or the elongation at break of the copper foil is 4% to 7%.

[0033] In any embodiment, under test conditions of room temperature (20 ± 10°C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is 700 MPa to 800 MPa and / or the elongation at break of the copper foil is 5% to 6%.

[0034] The copper foil exhibits good tensile strength and can therefore, to a certain extent, meet the practical requirements for high-strength copper foil in battery applications. Furthermore, the copper foil displays excellent elongation at break and good plasticity, which helps to reduce brittle defects in the copper foil and decrease the risk of breaks or small cracks in the copper foil within the cell.

[0035] In any embodiment, the hardness of the copper foil is between 55 HV and 65 HV. A suitable hardness is advantageous for the surface treatment of the copper foil and the cold-pressing treatment of the secondary battery, thereby reducing surface damage to the copper foil and minimizing the impact on the bonding performance between the negative electrode film layer and the copper foil.

[0036] In any embodiment, the thickness of the copper foil ranges from 4 µm to 10 µm. This copper foil can be made thinner without compromising its strength, which contributes to a lighter battery design and further improves the energy density or specific capacity.

[0037] In any embodiment, the secondary battery further comprises a negative electrode film layer located on at least one side of the copper foil, wherein a negative electrode active material in the negative electrode film layer comprises at least one of synthetic graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate, and metallic lithium. The secondary battery can be suitable for a variety of different negative electrode battery systems and offers broad applicability.

[0038] In any embodiment, the negative electrode active material comprises a silicon-based material, and the silicon-based material comprises at least one of elemental silicon, a silicon oxide compound, a silicon-carbon composite, a silicon-nitrogen composite, and a silicon alloy. The secondary battery that uses the silicon-based material as the negative electrode active material exhibits a higher energy density. Simultaneously, the copper foil in the secondary battery can effectively inhibit the volume expansion of the negative electrode during the battery cycle.

[0039] In any embodiment, the mass fraction of the silicon-based material, based on the total mass of the negative electrode film layer, is 5% to 100%, optionally 10% to 60%, and further optionally 10% to 30%.

[0040] In any embodiment, the mass fraction of the element silicon in the silicon-based material is 20% to 50%.

[0041] In any embodiment, the mass fraction of the element silicon, based on the total mass of the negative electrode film layer, is 4% to 10%.

[0042] In any embodiment, the expansion force of the secondary battery is greater than or equal to 1000 kgf.

[0043] In any embodiment, the expansion force of the secondary battery is greater than or equal to 2500 kgf.

[0044] In any embodiment, the expansion force of the secondary battery is greater than or equal to 4000 kgf.

[0045] In any embodiment, the expansion force of the secondary battery ranges from 1000 kgf to 10000 kgf.

[0046] 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.

[0047] In any embodiment, the thickness expansion rate of the secondary battery is 4% to 10%.

[0048] The current collector in the prior art tends to break under the expansion stress caused by the volume change of the secondary battery, leading to a drop in the secondary battery's performance and potentially to safety hazards, thus limiting further improvements in the secondary battery's performance. The current collector provided in the embodiments of the present application exhibits good strength properties, making it suitable for secondary batteries with a high rate of thickness expansion, and contributes to further improvements in the energy density and safety of the secondary battery.

[0049] A manufacturing process for a secondary battery is provided, comprising manufacturing a copper foil by electroplating process, wherein the electroplating process includes applying a pulse current to an electroplating solution such that copper ions in the electroplating solution are reduced and deposited to form the copper foil, wherein the peak value of the pulse current is 40000 A to 100000 A, the trough value of the pulse current is 100 A to 20000 A, and the change period of the current is 50 ms to 5000 ms.

[0050] Compared to rolling, the electroplating process is mature and simple, placing lower demands on equipment. The resulting copper foil exhibits excellent tensile strength and elongation at break, as well as outstanding mechanical strength and good plasticity.

[0051] The manufacturing process of the secondary battery comprises manufacturing an electrode sheet using the copper foil as a current collector; the manufacturing of the copper foil comprises manufacturing the copper foil by electroplating process, wherein the electroplating process comprises applying the pulse current to the electroplating solution such that copper ions in the electroplating solution are reduced and deposited to form the copper foil, wherein the peak value of the pulse current is 40000 A to 100000 A, the trough value of the pulse current is 100 A to 20000 A, and the period of change of the current is 50 ms to 5000 ms; and the expansion force of the secondary battery is greater than or equal to 1000 kgf.

[0052] In the manufacturing process of the secondary battery, the aforementioned electroplating process is used to produce the copper foil in order to obtain a copper foil with excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity and reducing the likelihood of fractures or cracks in the copper foil when subjected to stresses caused by the expansion force and / or the expansion of the thickness of the secondary battery, which in turn is caused by several factors – including the volume expansion of the electrode sheet in the secondary battery and gas formation due to electrolyte solution decomposition, leading to an increase in internal pressure, thus further improving the safety and service life of the secondary battery.

[0053] The manufacturing process of the secondary battery comprises manufacturing a wound secondary battery and manufacturing an electrode sheet using the copper foil as a current collector; the manufacturing of the copper foil comprises manufacturing the copper foil by electroplating process, wherein the electroplating process comprises applying the pulse current to the electroplating solution such that copper ions in the electroplating solution are reduced and deposited to form the copper foil, wherein the peak value of the pulse current is 40000 A to 100000 A, the trough value of the pulse current is 100 A to 20000 A, and the period of change of the current is 50 ms to 5000 ms; and the expansion force of the secondary battery is greater than or equal to 1000 kgf.

[0054] In the manufacturing process of the secondary battery, the aforementioned electroplating process is used to produce the copper foil in order to obtain a copper foil with excellent tensile strength and elongation at break, thereby improving the mechanical strength while maintaining excellent plasticity, and reducing the likelihood of the copper foil tearing or breaking under expansion stress after the secondary battery has been wound, pressurized and shaped, and reducing the likelihood of fractures in the electrode sheet of the wound cell, thus further improving the safety and service life of the secondary battery.

[0055] The manufacturing process comprises producing an electrode sheet using the copper foil as a current collector; the production of the copper foil comprises producing the copper foil by electroplating process, wherein the electroplating process comprises applying the pulse current to the electroplating solution such that copper ions in the electroplating solution are reduced and deposited to form the copper foil, wherein the peak value of the pulse current is 40000 A to 100000 A, the trough value of the pulse current is 100 A to 20000 A, and the period of change of the current is 50 ms to 5000 ms; and the capacity per gram of the negative electrode active material in the negative electrode film layer of the secondary battery is 800 mAh / g to 1500 mAh / g.

[0056] In the manufacturing process of the secondary battery, the aforementioned electroplating process is used to produce the copper foil in order to obtain a copper foil with excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity and reducing the likelihood of the copper foil breaking or tearing when subjected to the expansion stress caused by the volume change of the particles of the high-capacity negative electrode active material per gram before and after the intercalation / deintercalation of the lithium ions, which further contributes to improving the safety and lifespan of the secondary battery.

[0057] The electroplating process meets one or more of the following conditions: (1) The peak value of the impulse current is 40000 A to 80000 A; (2) The trough value of the impulse current is 1000 A to 10000 A; (3) The period of change of the impulse current is 500 ms to 5000 ms; (4) The distance between the cathode electrode and the anode electrode is 8 mm to 20 mm; (5) The temperature of the electroplating process is 45 °C to 60 °C; (6) The roller speed of the cathode roller is 2 m / min to 5 m / min. The electroplating process meets one or more of the following conditions: (1) The peak value of the impulse current is 50000 A to 70000 A; (2) The trough value of the impulse current is 2000 A to 5500 A; (3) The period of change of the impulse current is 2000 ms to 4000 ms; (4) The distance between the cathode electrode and the anode electrode is 8 mm to 12 mm; (5) The temperature of the electroplating process is 50 °C to 60 °C; (6) The roller speed of the cathode roller is 2 m / min to 3 m / min.

[0058] Compared to direct current deposition, applying a pulsed current to the electroplating solution can reduce and deposit copper ions to form fine crystal grains with smaller particle sizes under high current conditions, and larger crystal grains (e.g., columnar crystals) under low current conditions. By adjusting the current intensity and the change period, the formation and growth of copper ion crystal nuclei can be controlled, thereby adjusting the size and morphology of the crystal grains, as well as the proportions of copper crystal grains with a particle size of 0.5 µm or less and those with a particle size greater than 0.5 µm. This improves the tensile strength and elongation at break of the copper foil.

[0059] The pulse current comprises one or more rectangular, sinusoidal, triangular, and sawtooth pulse currents. The pulse current includes a sinusoidal pulse current. The continuous and periodic changes of the sinusoidal pulse current promote the continuous and variable growth of the crystal grains.

[0060] The electroplating solution comprises a leveling agent, a wetting agent and a glazing agent, wherein the leveling agent comprises one or more of collagen and sodium saccharin, the wetting agent comprises one or more of hydroxyethylcellulose and polyethylene glycol, and the glazing agent comprises bis-(sodium sulfopropyl)disulfide.

[0061] The leveling agent can increase the flatness of the copper foil, the wetting agent can improve the wettability of the electroplating solution and the substrate, increase the nucleation rate of the copper foil and reduce the average particle size of the crystal grains in the copper foil, and the brightening agent can refine the crystal grain size of the copper foil, reduce the surface roughness of the copper foil and improve the smoothness of the surface.

[0062] The electroplating solution comprises collagen with a concentration of 60 mg / L to 300 mg / L, sodium saccharin with a concentration of 0.5 g / L to 10 g / L, polyethylene glycol with a concentration of 50 mg / L to 200 mg / L, hydroxyethylcellulose with a concentration of 30 mg / L to 200 mg / L, bis-(sodium sulfopropyl)disulfide with a concentration of 500 mg / L to 2000 mg / L and chloride ions (calculated as chlorine atoms) with a concentration of 20 mg / L to 80 mg / L.

[0063] The electroplating solution comprises collagen with a concentration of 80 mg / L to 150 mg / L, sodium saccharin with a concentration of 0.5 g / L to 4 g / L, polyethylene glycol with a concentration of 60 mg / L to 150 mg / L, hydroxyethylcellulose with a concentration of 50 mg / L to 150 mg / L, bis-(sodium sulfopropyl)disulfide with a concentration of 500 mg / L to 1000 mg / L and chloride ions with a concentration of 40 mg / L to 80 mg / L.

[0064] The collagen and sodium saccharin in the electroplating solution help to improve the surface depressions and protrusions of the copper foil and increase its flatness. The hydroxyethylcellulose and polyethylene glycol are beneficial in reducing thickness variations in the copper foil and improving its uniformity. The bis(sodium sulfopropyl) disulfide can increase the electrochemical reduction rate of copper ions and adjust the particle size of the crystal grains. Copper foil produced in this way is bright and smooth, exhibits appropriate proportions of copper crystal grains with a particle size of less than or equal to 0.5 µm and those with a particle size greater than 0.5 µm, and possesses good tensile strength and elongation at break.

[0065] The pH value of the electroplating solution is 2.5 to 4.5, which facilitates the reduction of copper ions.

[0066] An electrode sheet is provided, wherein the electrode sheet comprises a copper foil in a secondary battery provided by the first aspect of the present application.

[0067] The electrode sheet further comprises a negative electrode film layer located on at least one side of the copper foil, wherein a negative electrode active material in the negative electrode film layer comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, lithium titanate and metallic lithium.

[0068] The negative electrode active material comprises a silicon-based material, and the silicon-based material comprises at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0069] The mass fraction of the silicon-based material, based on the total mass of the negative electrode film layer, is 5% to 100%, optionally 10% to 60% and optionally 10% to 30%.

[0070] The mass fraction of the element silicon in the silicon-based material is 20% to 50%.

[0071] The mass fraction of the element silicon, based on the total mass of the negative electrode film layer, is 4% to 10%.

[0072] A wound secondary battery is provided, comprising a secondary battery provided by the first aspect of the present application.

[0073] A second aspect of the present application provides a power-consuming device comprising a secondary battery of the first aspect of the present application. Brief description of the drawings

[0074] 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 representation of a secondary battery of an embodiment of the present application. Fig. 2 is an exploded view of the in Fig.1 Secondary battery of the embodiment of the present application shown. Fig. Figure 3 is a schematic representation of a battery module of an embodiment of the present application. Fig. Figure 4 is a schematic representation of a battery pack of an embodiment of the present application. Fig. 5 is an exploded view of the in Fig. 4 battery packs shown in the embodiment of the present application. Fig. Figure 6 is a schematic representation of a power-consuming device that uses a secondary battery as a power source in an embodiment of the present application. Fig. Figure 7 shows an inverse pole figure distribution diagram obtained by electron backscatter diffraction (EBSD) testing on a cross-section of a copper foil of embodiment 1 of the present application. Fig.Figure 8 shows a tensile force-strain curve of the copper foil of embodiment 1 of the present application. Fig. Figure 9 shows a diagram of the particle size distribution obtained after the EBSD diffraction test on the cross-section of the copper foil of embodiment 1 of the present application. Fig. Figure 10 shows an inverse pole figure distribution diagram obtained by the EBSD test on a cross-section of a copper foil of embodiment 2 of the present application. Fig. Figure 11 shows a tensile force-strain curve of the copper foil of embodiment 2 of the present application. Fig. Figure 12 shows a diagram of the particle size distribution obtained after the EBSD diffraction test on the cross-section of the copper foil of embodiment 2 of the present application. Fig.Figure 13 shows an inverse pole figure distribution diagram obtained by the EBSD test on a cross-section of a copper foil of embodiment 3 of the present application. Fig. Figure 14 shows a tensile force-strain curve of the copper foil of embodiment 3 of the present application. Fig. Figure 15 shows a diagram of the particle size distribution obtained after the EBSD diffraction test on the cross-section of the copper foil of embodiment 3 of the present application. Fig. Figure 16 shows a tensile force-strain curve of the copper foil of embodiment 3 of the present application. Fig. Figure 17 shows an inverse pole figure distribution diagram obtained by the EBSD test on a cross-section of a copper foil of comparative example 2 of the present application. Fig. Figure 18 shows the tensile force-strain curve of the copper foil of comparative example 2 of the present application. Fig.Figure 19 shows a diagram of the particle size distribution obtained after the EBSD diffraction test on the cross-section of the copper foil of Comparative Example 2 of the present application. Reference symbol list:

[0075] 1. Battery pack; 2. Upper housing body; 3. Lower housing body; 4. Battery module; 5. Secondary battery; 51. Housing body; 52. Electrode assembly; 53. Cover plate; T. Thickness direction. Detailed descriptions

[0076] The following section describes in detail embodiments of a secondary battery, an electrode sheet, a wound secondary battery, and a current-consuming device specifically disclosed in the present application, possibly with reference to the 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.

[0077] 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 ranges of 60 to 120 and 80 to 110 are listed for a particular parameter, then ranges of 60 to 110 and 80 to 120 are also conceivable. Furthermore, if minimum range values ​​of 1 and 2 and maximum range values ​​of 3, 4, and 5 are listed, then 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.

[0078] Unless otherwise stated, all embodiments and optional embodiments of the present application may be combined to form a new technical solution.

[0079] Unless otherwise stated, all technical features and optional technical features of the present application may be combined to form a new technical solution.

[0080] 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 includes steps (a) and (b), which means that the method may include steps (a) and (b) carried out sequentially, or that it may include steps (b) and (a) carried out sequentially. Similarly, when it is mentioned that the method may further include step (c), this means that step (c) may be added in any order. For example, the method may include steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), etc.

[0081] 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.

[0082] 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).

[0083] A typical secondary battery comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During charging and discharging, active ions (e.g., lithium or sodium ions) intercalate and deintercalate between the positive and negative electrode sheets. The electrolyte conducts the active ions between these two sheets. The separator, positioned between the positive and negative electrode sheets, primarily prevents short circuits while allowing the active ions to pass through. The negative electrode sheet includes a negative electrode current collector, which holds the electrode active material and collects the output current.Furthermore, it can inhibit cell expansion to prevent anode breakage during the cycle.

[0084] Increasing the amount of active material can improve the energy density or capacity of the secondary battery, but it also increases the cell's volume. While using silicon-based negative electrode materials, high-capacity graphite, lithium metal, and other negative electrode materials can also improve the energy density or capacity of the secondary battery, these materials exhibit high extensibility, leading to significant expansion and contraction of the electrode sheet during cycling. This can easily cause the copper foil in the cell to break or develop small cracks, triggering short circuits and seriously compromising the secondary battery's safety.Especially when constructing a square-wound battery, higher demands are placed on the bending strength of the current collector, as the cell is pressurized and shaped after winding. Pressurization and shaping of the cell lead to irreversible damage to the current collector. Using thinner current collector substrates, a high coating area of ​​active material, or a design with an extreme group span significantly increases the risk of cell cracking, further raising the risk of cell failure. Currently, the tensile strength of the commonly used copper foil for the negative electrode current collector is typically 200 MPa to 500 MPa, which does not meet the requirements for the high energy density or high capacity of the new generation of secondary batteries.Refining the copper crystal grains can improve material strength, but it can also exacerbate brittle defects in the copper foil and increase the risk of fractures or small cracks. The question of how to improve the strength of the copper foil without sacrificing good plasticity is a pressing problem that needs to be solved. [Secondary battery]

[0085] On this basis, the present application provides a secondary battery, wherein the secondary battery comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, the negative electrode current collector comprising a copper foil, the copper foil comprising copper crystal grains of different particle sizes, the copper crystal grains comprising copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm in the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm represents 5% to 30% of the total number of copper crystal grains.

[0086] Copper crystal grains with a particle size greater than 0.5 µm tend to appear as columnar or quasi-columnar crystal grains, which are also referred to here as "large crystal grains". Copper crystal grains with a particle size of 0.5 µm or less appear as fine crystal grains, resembling a granular form, and form a region of fine crystal grains surrounding the columnar crystal grains. Therefore, a copper foil substrate in the present application is formed with a crystal grain morphology consisting mainly of fine crystal grains with an admixture of larger crystal grains. Thus, it exhibits a heterogeneous crystal grain morphology in which fine crystal grains are interspersed with a small amount of large crystal grains. The main reason for this heterogeneous morphology with differently sized and small crystal grains lies in the control of the crystal grain size during foil formation.In particular, as an embodiment, the crystal grain size can be controlled by adjusting the current during the foil formation of the copper foil. When the current is reduced, the crystal grains tend to form larger crystals, and when the current is increased, the crystal grains tend to form smaller crystals.

[0087] Copper crystal grains with a particle size of 0.5 µm or less contribute to improving the tensile strength of the copper foil and increasing its mechanical properties; copper crystal grains with a particle size greater than 0.5 µm contribute to improving the elongation at break and increasing the plasticity of the copper foil. The proportions of copper crystal grains with a particle size of 0.5 µm or less and those with a particle size greater than 0.5 µm, relative to the total number of copper crystal grains, can influence the mechanical properties and plasticity of the copper foil to varying degrees, resulting in the copper foil exhibiting different levels of mechanical properties and plasticity overall.In the copper foil provided by the present application, the proportion of copper crystal grains with a particle size of less than or equal to 0.5 µm is 70% to 95% of the total number of copper crystal grains, which can significantly improve the tensile strength of the copper foil. At the same time, the proportion of copper crystal grains with a particle size greater than 0.5 µm is 5% to 30% of the total number of copper crystal grains, which can give the copper foil good elongation at break and provide a material basis for improving the energy density and safety of the secondary battery.

[0088] In some embodiments, the expansion force of the secondary battery is greater than or equal to 1000 kgf, and the secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, wherein the negative electrode current collector comprises a copper foil, wherein the copper foil comprises copper crystal grains of different particle sizes, wherein the copper crystal grains comprise copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm in the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm represents 5% to 30% of the total number of copper crystal grains.

[0089] During the charging and discharging cycle of a secondary battery, the intercalation / deintercalation of active ions leads to a volume expansion of the electrode sheet, particularly in batteries with a self-generated negative electrode or with newer silicon-based or lithium-metal negative electrodes. To increase the energy density of individual cells, cells with a high group span or large dimensions are developed. These factors combine to result in an overall greater expansion of the secondary battery.However, the high-expansion copper foil current collector of the secondary battery is subjected to considerable stretching and stress compression during operation, which increases the likelihood of fractures or cracks in the copper foil current collector and impairs the safety and service life of the battery cell; for this purpose, the secondary battery provided by the present application uses copper foil comprising the aforementioned copper crystal grains of different particle sizes.It exhibits excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity, and reducing the likelihood of fractures or cracks in the copper foil current collector in a high-expansion system, which has a positive effect on extending the service life of the secondary battery until cracks and failures of the electrode sheet occur and on further improving the safety and service life of the secondary battery.

[0090] In some embodiments, the thickness expansion rate of the secondary battery is 4% to 10%.

[0091] In some embodiments, the secondary battery is a wound secondary battery and the expansion force of the secondary battery is greater than or equal to 1000 kgf;The wound secondary battery comprises a negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, wherein the negative electrode current collector comprises a copper foil, the copper foil comprising copper crystal grains of different particle sizes, wherein the copper crystal grains comprise copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5% to 30%.

[0092] The current collector of the negative electrode sheet in a wound secondary battery is prone to cracking at the corners. This occurs because the cell is subjected to pressure and deformation after winding, which can easily lead to irreversible damage to the current collector. This significantly increases the likelihood of cracks or fractures forming in the outer corner and inner bending areas of the negative electrode sheet after being subjected to expansion stress caused by factors such as increased internal pressure and volume expansion of the secondary battery. This increases the risk of cell failure and reduces the lifespan and safety of the secondary battery.In the wound secondary battery provided by the present application, the copper foil utilizes copper crystal grains of varying particle sizes, as described above. This significantly improves the tensile strength and elongation at break of the copper foil, resulting in excellent mechanical properties and plasticity. This reduces the likelihood of cracks or fractures forming in the copper foil under expansion stress and the probability of fractures in the electrode sheet of the wound cell. Consequently, it positively extends the service life of the secondary battery before cracks and electrode sheet failures occur, further enhancing the safety and lifespan of the secondary battery.

[0093] In some embodiments, the thickness expansion rate of the wound secondary battery is 4% to 10%. Increasing the amount of active material is one of the effective measures for improving the energy density or capacity of the secondary battery, but this leads to an increase in the cell volume; the applicants have found that by using the negative electrode active material with a high capacity per gram, the available lithiation capacity of the negative electrode active material can be significantly increased, thus increasing the energy density or capacity of the secondary battery while minimizing the impact on the cell volume.However, the negative electrode active material with high capacity per gram exhibits a greater volume expansion of the particles before and after the intercalation / deintercalation of the lithium ions, and the expansion stress acts on the copper foil of the electrode current collector, increasing the likelihood that the copper foil will break or tear under the expansion stress along the thickness direction, thus deteriorating the safety and lifespan of the secondary battery.

[0094] Based on this, a further embodiment of the present application proposes a secondary battery, wherein the secondary battery comprises a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer arranged on at least one side face of the negative electrode current collector, the negative electrode current collector comprising a copper foil, the copper foil comprising copper crystal grains of different particle sizes, the copper crystal grains comprising copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm in the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm of the total number of copper crystal grains is 5% to 30%; and wherein the capacity per gram of the negative electrode active material in the negative electrode film layer is 800 mAh / g to 1500 mAh / g.

[0095] The secondary battery provided by the present application uses copper foil comprising the aforementioned copper crystal grains of varying particle sizes. It exhibits excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity, and it is well suited to the negative electrode active material with high capacity per gram, thus improving the energy density and capacity of the secondary battery while also increasing its safety and lifespan.

[0096] In some embodiments, the capacity per gram of negative electrode active material in the negative electrode film layer is 800 mAh / g to 1500 mAh / g.

[0097] The copper foil provided by the present application is particularly suitable for a system comprising a negative electrode active material with a capacity per gram in the range of 800 mAh / g to 1500 mAh / g. More active ions can be intercalated into the high-capacity-per-gram negative electrode material (such as silicon-based negative electrodes, alkali metal negative electrodes, etc.), so it typically exhibits high extensibility, which increases the likelihood of the copper foil breaking or tearing in the cell. However, the copper foil according to the present application simultaneously possesses excellent mechanical properties and plasticity, which can reduce the risk of the copper foil breaking or tearing in a high-energy-density or high-extensibility battery system.

[0098] Without being bound to any specific theory, large and fine crystal grains exhibit distinctly different work-hardening capabilities. The heterogeneous grain morphology, in which fine crystal grains are interspersed with a small amount of large crystal grains, leads to more pronounced strain zoning in the early stages of plastic deformation of the copper foil. This could be due to the fact that the moderate admixture of large crystal grains—compared to a structure consisting entirely of fine crystal grains—generates a higher density of geometrically necessary dislocations during inhomogeneous plastic deformation. The uneven plastic deformation process of the copper foil can cause the crystal planes of the crystal grains to bend, resulting in dislocations. These dislocations are referred to as geometrically necessary dislocations (GNDs).The geometrically necessary dislocations can coordinate the plastic strain caused by deformation and maintain material continuity. This helps to reduce the occurrence of concentrated stresses during the deformation of the copper foil, resulting in a greater ability of the copper foil to suppress strain localization and improving its plasticity. Furthermore, the contact interface between the crystal grains in the copper foil crystal is called the crystal grain boundary. It is understandable that in the same region, the total area of ​​the crystal grain boundaries is higher for crystal grains with smaller particle sizes. Consequently, the copper foil must overcome higher crystal grain boundary stresses during the deformation process, leading to higher deformation resistance of the copper foil and thus improved mechanical strength.At the same time, the formation of a higher geometrically necessary dislocation density in the copper foil during deformation contributes to the reduction of concentrated stresses and can improve mechanical strength.

[0099] In some embodiments, the proportion of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 75% to 95%, 80% to 95%, 85% to 95%, 83% to 93%, 85% to 93% or 87% to 93%, which helps to further improve the tensile strength and optimize the mechanical properties of the copper foil.

[0100] In some embodiments, the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 75%, 78%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94% or 95%, or lies in a range between any two of the above values ​​or is any value between the ranges.

[0101] This includes the particle size range of the copper crystal grains with a particle size of less than or equal to 0.5 µm, greater than or equal to 0.1 µm and less than or equal to 0.5 µm.

[0102] In some embodiments, the proportion of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5% to 20%, 2% to 20%, 2% to 15%, 5% to 15%, 5% to 13%, 6% to 12% or 7% to 10%, which helps to further improve the elongation at break and optimize the plasticity of the copper foil.

[0103] In some embodiments, the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 18%, 20%, 25% or 30%, or lies in a range between any two of the above values ​​or is any value between the ranges.

[0104] This includes the particle size range of the copper crystal grains with a particle size greater than 0.5 µm and less than or equal to 3 µm, which helps to reduce or optimize the average particle size of the copper foil and improve the tensile strength of the copper foil.

[0105] The number and particle size of crystal grains in copper foil can be determined using established techniques. As an example, the cross-section of the copper foil is measured using an electron backscatter diffraction (EBSD) instrument and scanning electron microscopy to obtain an inverse pole figure distribution plot at a magnification of 3000x. The number and particle size of the crystal grains are then statistically evaluated using the imageJ analysis software included with the Oxford C-Nano+ electron backscatter diffraction instrument. The equivalent circular diameter of the crystal grains is used as the particle size to generate a number distribution plot. Subsequently, a skewness distribution is fitted to determine the particle size of the crystal grains and the proportion of crystal grains in different particle size intervals.

[0106] In some embodiments, the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm and less than or equal to 3 µm, based on the total number of copper crystal grains, is 5% to 30%.

[0107] As mentioned above, the particle size of the copper crystal grains in the range of greater than 0.5 µm and less than or equal to 3 µm can help to reduce the average particle size of the copper foil and further improve the mechanical strength of the copper foil; by further controlling the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm and less than or equal to 3 µm to 5% to 30%, the copper foil can exhibit good elongation at break and both excellent mechanical properties and plasticity, which can reduce the risk of the copper foil breaking or tearing in a high-energy-density battery system or in a high-expansion battery system, thus enabling a simultaneous increase in the energy density and safety of the secondary battery.

[0108] In some embodiments, the capacity per gram of negative electrode active material is 800 mAh / g, 820 mAh / g, 850 mAh / g, 880 mAh / g, 900 mAh / g, 920 mAh / g, 950 mAh / g, 980 mAh / g, 1000 mAh / g, 1020 mAh / g, 1050 mAh / g, 1080 mAh / g, 1100 mAh / g, 1120 mAh / g, 1150 mAh / g, 1180 mAh / g, 1200 mAh / g, 1250 mAh / g, 1300 mAh / g, 1350 mAh / g, 1400 mAh / g, 1450 mAh / g, or 1500 mAh / g, or lies in a range between any two of the above. The values ​​mentioned above, or any value between the ranges.

[0109] When used in this text, the capacitance per gram of the negative electrode active material can be measured using equipment and methods known in the trade. As an example, the determination can be carried out using the following method: The negative electrode active material, along with the conductive agent carbon black and polyvinylidene fluoride (PVDF), are thoroughly stirred and mixed in a mass ratio of 91.6 : 1.8 : 6.6 in a suitable quantity of the solvent NMP to form a uniform negative electrode paste; the negative electrode paste is applied uniformly to the surface of the copper foil of the negative electrode current collector, dried, and cold-pressed; then, a metallic lithium sheet is used as the counter electrode and a polypropylene film (PP film) as the separator, and an electrolyte solution is injected.The electrolyte solution is composed as follows: Dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and ethylene carbonate (EC) are mixed in a weight ratio of 1:1:1 to obtain an organic solvent. LiPF6 is then dissolved in this organic solvent to produce an electrolyte solution with a concentration of 1.0 mol / L. A CR2430 button cell is assembled in an argon-sealed glove box. At 25 °C, the button cell is charged at a rate of 0.1 C to the upper charge limit voltage of 3.8 V and then charged at a constant voltage until the current is less than 0.05 C. After a 30-minute rest period, it is discharged at a rate of 0.1 C to the lower cutoff voltage of 2.0 V. The initial discharge capacity is recorded as Cm, followed by the capacity per gram of negative electrode active material = discharge capacity Cm / mass m of negative electrode active material.

[0110] It is understandable that the capacity per gram of the negative electrode active material can also be determined by disassembling the battery, obtaining the negative electrode sheet, assembling it into a button cell according to the method described above, and then testing it.

[0111] In some embodiments, the short diameter of at least some of the copper crystal grains with a particle size greater than 0.5 µm is arranged along the thickness direction of the current collector.

[0112] The short diameter of at least some of the copper crystal grains with a particle size greater than 0.5 µm is oriented along the thickness direction of the current collector, indicating that the tortuosity of the crystal grain boundary pattern within the copper foil is high and that the energy required to fracture the copper foil along the crystal grain boundaries (i.e., along the thickness direction of the current collector) is higher. This helps to reduce the probability of fractures of the copper foil along the thickness direction, increases the brittleness of the current collector, and further reduces the risk of fractures or cracks in the copper foil, thereby improving the safety of the secondary battery.

[0113] It is understandable that the arrangement direction of the short diameter of at least some of the copper crystal grains with a particle size greater than 0.5 µm can be characterized and determined with reference to the previously described combination with EBSD and scanning electron microscopy.

[0114] In some embodiments, the average particle size of the copper crystal grains is 0.3 µm to 1.2 µm. In some embodiments, the average particle size of the copper crystal grains is 0.3 µm to 0.6 µm. In some embodiments, the average particle size of the copper crystal grains is 0.3 µm to 0.5 µm. In some embodiments, the average particle size of the copper crystal grains is 0.3 µm, 0.35 µm, 0.4 µm, 0.45 µm, 0.5 µm, 0.55 µm, 0.6 µm, 0.65 µm, 0.7 µm, 0.75 µm, 0.8 µm, 0.85 µm, 0.9 µm, 1.0 µm, 1.1 µm or 1.2 µm, or lies in a range between any two of the above values ​​or is any value between the ranges.

[0115] Theoretically, a suitable particle size range contributes to the copper foil having suitable crystal grain boundaries, which gives the copper foil adequate resistance to crystal grain dislocation movements and deformation resistance, thus optimizing the mechanical strength of the copper foil.

[0116] The average grain size of the crystal particles can be determined using established methods. As an example, the cross-section of the copper foil is measured in combination with an electron backscatter diffraction (EBSD) instrument and scanning electron microscopy to obtain an inverse pole figure distribution plot. Using the imageJ analysis software, which is part of the Oxford C-Nano+ electron backscatter diffraction instrument, the number and particle size of the crystal particles are statistically evaluated. The equivalent circular diameter of the crystal particles is used as the particle size to generate a numerical distribution plot. Subsequently, a skewness distribution is used to fit the plot and obtain the average particle size of the crystal particles.

[0117] In some embodiments, the maximum particle size of the copper crystal grains is 1 µm to 2.5 µm. In some embodiments, the maximum particle size of the copper crystal grains is 1.2 µm to 1.8 µm or 1.2 µm to 2.0 µm. In some embodiments, the maximum particle size of the copper crystal grains is 1 µm, 1.2 µm, 1.4 µm, 1.6 µm, 1.8 µm, or 2 µm, or lies within a range between any two of the above values, or is any value between the ranges.

[0118] The maximum particle size of the copper crystal grains can be determined using established techniques. As an example, the cross-section of the copper foil is measured in combination with an electron backscatter diffraction (EBSD) instrument and scanning electron microscopy to obtain an inverse pole-figure distribution plot. Using the imageJ analysis software included with the Oxford C-Nano+ electron backscatter diffraction instrument, the number and particle size of the crystal grains are statistically evaluated. The equivalent circular diameter of the crystal grains is used as the particle size to generate a numerical distribution plot. Subsequently, a skewness distribution is used for fitting. In the statistical results, the maximum particle size of the crystal grains is the maximum particle size of the copper crystal grains.

[0119] In some embodiments, the minimum particle size of the copper crystal grains is 0.1 µm to 0.3 µm. In some embodiments, the minimum particle size of the copper crystal grains is 0.1 µm, 0.15 µm, 0.2 µm, 0.25 µm, or 0.3 µm, or lies in a range between any two of the above values, or is any value between the ranges.

[0120] The minimum particle size of the copper crystal grains can be determined using established technical methods. As an example, the cross-section of the copper foil is measured in combination with an electron backscatter diffraction (EBSD) instrument and scanning electron microscopy to obtain an inverse pole figure distribution plot. Using the imageJ analysis software included with the Oxford C-Nano+ electron backscatter diffraction instrument, the number and particle size of the crystal grains are statistically evaluated. The equivalent circular diameter of the crystal grains is used as the particle size to generate a numerical distribution plot. Subsequently, a skewness distribution is used for fitting. In the statistical results, the minimum particle size of the crystal grains is the minimum particle size of the copper crystal grains.

[0121] The particle size range between the maximum and minimum particle sizes is the difference between the maximum and minimum particle sizes in the particle size distribution of the copper foil crystal grains. In some embodiments, the particle size range of the copper crystal grains is 0.8 µm to 2.5 µm. In some embodiments, the particle size range of the copper crystal grains is 0.8 µm to 2 µm. In some embodiments, the particle size range of the copper crystal grains is 1 µm to 2 µm. In some embodiments, the particle size range of the copper crystal grains is 0.8 µm, 1 µm, 1.2 µm, 1.4 µm, 1.6 µm, 1.8 µm, 2.0 µm, 2.2 µm, 2.4 µm or 2.5 µm, or lies in a range between any two of the above values ​​or is any value between the ranges.

[0122] The particle size range of the copper crystal grains within the aforementioned range can maintain the discrete degree of particle size distribution within a suitable range, which can help to accommodate both the area of ​​the grain boundaries and the geometrically required dislocation density of the copper crystal grains, improve resistance to crystal grain dislocation movements, and reduce the occurrence of concentrated stresses during the deformation of the copper foil, thus contributing to the copper foil exhibiting improved mechanical strength and excellent plasticity.

[0123] In some embodiments, under test conditions of room temperature (20 ± 10 °C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is 600 MPa to 1000 MPa. In some embodiments, the tensile strength of the copper foil is 700 MPa to 1000 MPa. In some embodiments, the tensile strength of the copper foil is 700 MPa to 800 MPa.

[0124] In some embodiments, under test conditions of room temperature (20 ± 10 °C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm), and a tensile speed of 50 ± 0.5 mm / min, the elongation at break of the copper foil is 4% to 8%. In some embodiments, the elongation at break of the copper foil is 4% to 7%. In some embodiments, the elongation at break of the copper foil is 5% to 6%.

[0125] In this text, the term "tensile strength" refers to the maximum load-bearing capacity per unit area of ​​a sample when it is continuously subjected to stress until it breaks.

[0126] In this text, 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 evaluating a material's ability to deform under tension during tensile stress.

[0127] 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 specimens with a length of 50 ± 0.25 mm and a width of 15 ± 0.25 mm are cut from a test area. At room temperature (20 ± 10 °C), the specimens are continuously loaded at a tensile rate of 50 ± 0.5 mm / min until they break. The tensile strength of the specimen is determined by dividing the maximum load by the cross-sectional area of ​​the specimen. The cross-sectional area of ​​the specimen can be calculated by dividing the mass of the specimen by the product of its length and density. The elongation at break can be calculated after the above test using the displacement method. The test area refers to the area covered during the instrument test.Since the sample may need to be fixed with a clamping device during testing, the length and width of the sample may be greater than the length and width of the test area.

[0128] In some embodiments, under test conditions of room temperature (20 ± 10 °C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min, the tensile strength of the copper foil is 600 MPa, 650 MPa, 700 MPa, 750 MPa, 800 MPa, 850 MPa, 900 MPa, 950 MPa or 1000 MPa, or lies in a range between any two of the above values ​​or is any value between the ranges.

[0129] In some embodiments, under test conditions of room temperature (20 ± 10 °C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min, the elongation at break of the copper foil is 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5% or 8.0%, or lies in a range between any two of the above values, or is any value between the ranges.

[0130] The copper foil with the aforementioned tensile strength and elongation at break has excellent mechanical strength and plasticity, and can be used for high energy density or high elongation batteries, which contributes to improving the safety of the secondary battery.

[0131] In some embodiments, the hardness of the copper foil is 55 HV to 65 HV. In some embodiments, the hardness of the copper foil is 55 HV to 60 HV. In some embodiments, the hardness of the copper foil is 55 HV, 56 HV, 57 HV, 58 HV, 59 HV, 60 HV, 61 HV, 62 HV, 63 HV, 64 HV or 65 HV, or lies in a range between any two of the above values, or is any value between the ranges.

[0132] The hardness can reflect the compressive strength or puncture resistance of the copper foil. During the manufacture of the secondary battery, the surface quality of the copper foil can affect the bonding performance between the negative electrode film layer and the copper foil. In particular, during the cold pressing step of the secondary battery, the particles of the negative electrode active material exert pressure on the copper foil when subjected to external pressure. Appropriate hardness helps to reduce surface damage to the copper foil and thus mitigate its impact on the bonding performance between the negative electrode film layer and the copper foil.

[0133] In some embodiments, the thickness of the copper foil is 4 µm to 10 µm. In some embodiments, the thickness of the copper foil is 3 µm, 4 µm, 5 µm, 6 µm, 7 µm, 8 µm, 9 µm and 10 µm, or lies in a range between any two of the above values, or is any value between the ranges.

[0134] 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.

[0135] When medium-strength copper foil is made thinner, the maximum load-bearing capacity decreases rapidly. The thickness of the copper foil available for plastic deformation is significantly reduced, leading to a marked decrease in the tensile strength and elongation at break of the copper foil. This makes the copper foil prone to fatigue fracture in the late cycle phase of the secondary battery, triggering safety failures. The copper foil provided by the present application still exhibits excellent tensile strength and elongation at break in a thickness range of 4 µm to 10 µm and possesses good mechanical properties and plasticity. The copper foil can be made thinner without compromising its strength, contributing to lighter battery construction and weight reduction, and further improving the energy density or specific capacity of the secondary battery.

[0136] In some embodiments, the expansion force of the secondary battery is greater than or equal to 1000 kgf.

[0137] In some embodiments, the expansion force of the secondary battery is greater than or equal to 2500 kgf.

[0138] In some embodiments, the expansion force of the secondary battery is greater than or equal to 4000 kgf.

[0139] In some embodiments, the expansion force of the secondary battery is 1000 kgf to 10000 kgf.

[0140] In some embodiments, the expansion force of the secondary battery is 1000 kgf, 1200 kgf, 1500 kgf, 1800 kgf, 2000 kgf, 2200 kgf, 2500 kgf, 2800 kgf, 3000 kgf, 3200 kgf, 3500 kgf, 3800 kgf, 4000 kgf, 4200 kgf, 4500 kgf, 4800 kgf, 5000 kgf, 5500 kgf, 6000 kgf, 6500 kgf, 7000 kgf, 7500 kgf, 8000 kgf, 8500 kgf, 9000 kgf, 9500 kgf or 10000 kgf, or lies in a range between any two of the above values, or is one any value between the ranges.

[0141] Here, 1 kgf refers to the force of gravity exerted on a 1-kilogram object at sea level at 45 degrees north latitude. 1 kgf is approximately equal to 9.8 newtons. The expansion force of the secondary battery cell refers to the expansion force of the secondary battery when it reaches 60% state of health (SOH). This can be detected by a pressure sensor located in a clamping device on both sides of the large surfaces of the electrode sheet of the secondary battery cell. As an example, the test is performed using the following method: At 25°C, the battery is charged to a voltage of 3.8 V at a constant current of 1 C, then charged to a current ≤ 0.05 C at a constant voltage of 3.8 V, and subsequently discharged to a voltage of 2.5 V at a constant current of 1 C – this constitutes one charge and discharge cycle. The charge and discharge cycle is repeated.The state of health (SOH) of the cell is monitored throughout the entire process. When 90% SOH is reached, the expansion force of the secondary battery at 90% SOH is measured using the pressure sensor located in the clamping device on both sides of the large surfaces of the secondary battery's electrode sheet. The expansion force of the secondary battery at 60% SOH is determined by simulating a simulation model.

[0142] 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.

[0143] In some embodiments, the thickness expansion rate of the secondary battery is 4% to 10%.

[0144] In the present application, the thickness expansion rate of the secondary battery can be determined using methods known in the art. For example, the thickness expansion rate is = (H1 - H0) / H0, where H0 and H1 are the total thickness of the secondary battery at 100% SOH and the total thickness of the secondary battery at 60% SOH, respectively. As an example, the determination can be carried out using the following method. At 25 °C, the total thickness H0 of the secondary battery is measured. The battery is then 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 is repeated. The SOH of the cell is monitored throughout the entire process.When the secondary battery reaches 90% state of health (SOH), its total thickness H' is measured. The total thickness H1 at 60% SOH is determined by simulating a model, allowing the rate of thickness expansion of the secondary battery to be calculated.

[0145] In some embodiments, the thickness expansion rate of the secondary battery is 4%, 5%, 6%, 7%, 8%, 9%, 10%, or lies in a range between any two of the above values.

[0146] The current collector in the prior art tends to break under the expansion stress caused by the volume change of the secondary battery, leading to a drop in the secondary battery's performance and potentially to safety hazards, thus limiting further improvements in the secondary battery's performance. The current collector provided in the embodiments of the present application exhibits good strength properties, making it suitable for secondary batteries with a high rate of thickness expansion, and contributes to further improvements in the energy density and safety of the secondary battery.

[0147] The secondary battery provided by the present application can be produced by a method comprising the following steps: producing a copper foil by electroplating process, wherein the electroplating process comprises applying a pulse current to an electroplating solution such that copper ions in the electroplating solution are reduced and deposited to form the copper foil, wherein the peak value of the pulse current is 40000 A to 100000 A, the trough value of the pulse current is 100 A to 20000 A, and the change period of the current is 50 ms to 5000 ms.

[0148] The term “galvanizing process” used herein refers to a process for depositing metal or alloys onto the surface of a workpiece using the principle of electroplating to form a metal layer.

[0149] The term “impulse current” used herein refers to current or voltage pulses that occur repeatedly in a cycle.

[0150] Compared to the state-of-the-art rolling process, the electroplating process is mature and simple, places lower demands on equipment, and results in lower manufacturing costs. The copper foil produced in this way exhibits excellent tensile strength and elongation at break, combining not only excellent mechanical strength with good plasticity, but also contributing to a reduction in the manufacturing costs of the secondary battery.

[0151] In some processes, a high direct current is used to produce copper foil through electroplating, thereby improving the mechanical strength of the copper foil. However, due to the small differences in workability between the crystal grains, the ability to suppress strain localization is reduced. The copper foil is very susceptible to concentrated stresses during deformation, its plasticity is reduced, and there is a high risk of brittle fracture.In the manufacturing process provided by the present application, a pulsed current is used to adjust the crystal nucleation and growth rate of the copper crystal grains by continuously changing the current, thereby adjusting the size and morphology of the copper crystal grains, adjusting the proportions of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm and the number of copper crystal grains with a particle size greater than 0.5 µm, and improving the tensile strength and elongation at break of the copper foil, so that the copper foil exhibits both excellent mechanical properties and plasticity.

[0152] The manufacturing process of the secondary battery comprises manufacturing an electrode sheet using the copper foil as a current collector; the manufacturing of the copper foil comprises manufacturing the copper foil by electroplating process, wherein the electroplating process comprises applying the pulse current to the electroplating solution such that copper ions in the electroplating solution are reduced and deposited to form the copper foil, wherein the peak value of the pulse current is 40000 A to 100000 A, the trough value of the pulse current is 100 A to 20000 A, and the period of change of the current is 50 ms to 5000 ms; and the expansion force of the secondary battery is greater than or equal to 1000 kgf.

[0153] In the manufacturing process of the secondary battery, the aforementioned electroplating process is used to produce the copper foil in order to obtain a copper foil with excellent tensile strength and elongation at break, thereby improving mechanical strength while maintaining excellent plasticity and reducing the likelihood of fractures or cracks in the copper foil when subjected to stresses caused by the expansion force and / or the expansion of the thickness of the secondary battery, which in turn is caused by several factors – including the volume expansion of the electrode sheet in the secondary battery and gas formation due to electrolyte solution decomposition, leading to an increase in internal pressure, thus further improving the safety and service life of the secondary battery.

[0154] The manufacturing process of the secondary battery comprises manufacturing a wound secondary battery and manufacturing an electrode sheet using the copper foil as a current collector; the manufacturing of the copper foil comprises manufacturing the copper foil by electroplating process, wherein the electroplating process comprises applying the pulse current to the electroplating solution such that copper ions in the electroplating solution are reduced and deposited to form the copper foil, wherein the peak value of the pulse current is 40000 A to 100000 A, the trough value of the pulse current is 100 A to 20000 A, and the period of change of the current is 50 ms to 5000 ms; and the expansion force of the secondary battery is greater than or equal to 1000 kgf.

[0155] In the manufacturing process of the secondary battery, the aforementioned electroplating process is used to produce the copper foil in order to obtain a copper foil with excellent tensile strength and elongation at break, thereby improving the mechanical strength while maintaining excellent plasticity, and reducing the likelihood of the copper foil tearing or breaking under expansion stress after the secondary battery has been wound, pressurized and shaped, and reducing the likelihood of fractures in the electrode sheet of the wound cell, thus further improving the safety and service life of the secondary battery.

[0156] In some embodiments, the peak value of the pulse current is 40,000 A to 80,000 A. In some embodiments, the peak value of the pulse current is 50,000 A to 70,000 A. In some embodiments, the peak value of the pulse current is 55,000 A to 70,000 A, 50,000 A to 80,000 A, 55,000 A to 80,000 A, or 50,000 A to 60,000 A.

[0157] In some embodiments, the peak value of the pulse current is 45000 A, 50000 A, 55000 A, 60000 A, 65000 A, 70000 A, 75000 A, 80000 A, 85000 A, 90000 A, 95000 A or 100000 A, or lies in a range between any two of the above values ​​or is any value between the ranges.

[0158] In some embodiments, the trough value of the pulse current is 1000 A to 10000 A. In some embodiments, the trough value of the pulse current is 2000 A to 5500 A. In some embodiments, the trough value of the pulse current is 2500 A to 5000 A, 2000 A to 8000 A, or 2000 A to 5000 A.

[0159] In some embodiments, the trough value of the pulse current is 100 A, 500 A, 1000 A, 1500 A, 2000 A, 2500 A, 3500 A, 4000 A, 4500 A, 5000 A, 8000 A, 10000 A, 15000 A or 20000 A, or lies in a range between any two of the above values ​​or is any value between the ranges.

[0160] In some embodiments, the change period of the pulse current is 500 ms to 5000 ms. In some embodiments, the change period of the pulse current is 2000 ms to 4000 ms. In some embodiments, the change period of the pulse current is 50 ms, 100 ms, 200 ms, 500 ms, 1000 ms, 1200 ms, 1500 ms, 1800 ms, 2000 ms, 2500 ms, 2750 ms, 3000 ms, 3500 ms, 4000 ms, 4500 ms, or 5000 ms, or lies in a range between any two of the above values, or is any value between the ranges.

[0161] The term "peak value" used herein refers to the maximum current value of the momentum current, usually the value at the peak of the momentum current waveform. Similarly, the term "valley value" refers to the minimum current value of the momentum current, usually the value at the trough of the momentum current waveform.

[0162] The term “period of change” used herein refers to the time between two adjacent peaks or troughs of the waveform of the momentum flux, and the unit is ms.

[0163] During the copper ion deposition process, increasing the current can accelerate the deposition rate of copper ions, contributing to the formation of fine crystal grains with smaller particle sizes; decreasing the current can decrease the deposition rate of copper ions, contributing to the formation of relatively regular and ordered crystal grains with larger particle sizes, such as columnar crystals. By adjusting the current change parameters, namely peak value, trough value, and period of change, the crystal nucleation of the copper crystal grains, the crystal grain growth rate, and the deposition time of the copper ions can be regulated, resulting in a heterogeneous crystal grain morphology with a mixed distribution of large and small crystal grains.By adjusting the particle size of the crystal grains and the proportions of the number of crystal grains with different particle sizes, the tensile strength and elongation at break of the copper foil are improved, so that the copper foil has both excellent mechanical strength and plasticity.

[0164] In some embodiments, the pulse current comprises one or more of rectangular pulse currents, sinusoidal pulse currents, triangular pulse currents, and sawtooth pulse currents.

[0165] In some embodiments, the pulse current comprises a sinusoidal pulse current. The continuous and periodic changes of the sinusoidal pulse current promote the continuous and variable growth of the crystal grains.

[0166] The manufacturing process is a continuous production process.

[0167] 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-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 through 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, 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.

[0168] In some embodiments, the cathode electrode is a titanium roller or plate.

[0169] In some embodiments, the anode electrode is a titanium substrate plate.

[0170] In some embodiments, the distance between the cathode electrode and the anode electrode is 8 mm to 20 mm. In some embodiments, the distance between the cathode electrode and the anode electrode is 8 mm to 12 mm. In some embodiments, the distance between the cathode electrode and the anode electrode is 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm, 16 mm, 17 mm, 18 mm, 19 mm, or 20 mm, or lies within any range between any two of the above values, or is any value within these ranges.

[0171] In some embodiments, the electroplating temperature is 45 °C to 60 °C. In some embodiments, the electroplating temperature is 50 °C to 60 °C. In some embodiments, the deposition temperature is optionally 45 °C, 50 °C, 55 °C, or 60 °C, lies within any two of the above values, or is any value within these ranges.

[0172] In some embodiments, the cathode roller speed is 2 m / min to 5 m / min. In some embodiments, the cathode roller speed is 2 m / min to 3 m / min. In some embodiments, the cathode roller speed is 2 m / min, 2.5 m / min, 3 m / min, 3.5 m / min, 4 m / min, 4.5 m / min, or 5 m / min, or lies within a range between any two of the above values, or is any value within these ranges.

[0173] The cathode roller can be any roller suitable for the production of copper foil, for example a titanium roller.

[0174] In some embodiments, the electroplating solution comprises a leveling agent, a wetting agent, and a glazing agent.

[0175] The term "leveling agent" used herein refers to a substance added to the electroplating solution to improve the flatness of the coating. It can adhere to the peaks of the copper foil with a fast deposition rate, inhibit crystal grain growth, equalize the growth rates of pits and peaks, and improve the flatness of the copper foil.

[0176] The term "wetting agent" used here 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. The wetting agent can improve the wettability of both 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 crystal grain size within the copper foil.

[0177] The term "polishing agent" used here refers to a substance that improves the smoothness of the coating and reduces surface roughness. The polishing agent can refine the crystal grain size of the copper foil, reduce the surface roughness of the copper foil, and improve the surface smoothness.

[0178] In some embodiments, the leveling agent comprises one or more collagens and sodium saccharins.

[0179] Without being bound to any specific theory, collagen can inhibit the deposition of copper ions and even out the growth rates of depressions and peaks. The addition of sodium saccharin attracts the copper ions deposited in the depressions on the surface of the copper foil, thereby reducing microscopic defects or irregularities in the foil and minimizing the warpage caused by these defects. Two different leveling agents further improve the surface depressions and protrusions of the copper foil and enhance its overall flatness.

[0180] In some embodiments, the concentration of collagen in the electroplating solution is 60 mg / L to 300 mg / L. In some embodiments, the concentration of collagen in the electroplating solution is 80 mg / L to 150 mg / L. In some embodiments, the concentration of collagen in the electroplating solution is 60 mg / L, 80 mg / L, 100 mg / L, 150 mg / L, 200 mg / L, 250 mg / L, or 300 mg / L, or lies within any range between any two of the above values, or is any value within these ranges.

[0181] Collagen can be selected as a protein with a molecular mass that is commonly used in the field of copper foils, for example collagen with a relative molecular mass of 8000 to 12000.

[0182] In some embodiments, the concentration of sodium saccharin in the electroplating solution is 0.5 g / L to 10 g / L. In some embodiments, the concentration of sodium saccharin in the electroplating solution is 0.5 g / L to 4 g / L. In some embodiments, the concentration of sodium saccharin in the electroplating solution is 0.5 g / L, 0.8 g / L, 1 g / L, 1.5 g / L, 2.0 g / L, 2.5 g / L, 3.0 g / L, 3.5 g / L, 4.0 g / L, 4.5 g / L, 5.0 g / L, 5.5 g / L, 6.0 g / L, 6.5 g / L, 7.0 g / L, 7.5 g / L, 8.0 g / L, 8.5 g / L, 9.0 g / L, 9.5 g / L, or 10 g / L, or lies within a range between any two of the above values ​​or is any value within these ranges. In some embodiments, the wetting agent comprises one or more hydroxyethylcellulose and polyethylene glycol.

[0183] Without being bound to any specific theory, hydroxyethylcellulose exhibits good water solubility and thickening properties, can form a uniform solution in water, increase the viscosity of the electroplating solution, and adhere to the substrate surface of the copper foil. As a lubricant and wetting agent, polyethylene glycol can reduce the surface tension of liquids and improve their wettability on solid surfaces. The combined use of these two can enhance the adhesive properties of the electroplating solution, promote and support the adhesion and deposition of copper ions on the substrate surface, improve the consistency of the crystal grains during the deposition process, reduce variations in crystal grain size in the thickness direction, improve the uniformity of the copper foil, and thus enhance its mechanical properties.

[0184] In some embodiments, the concentration of polyethylene glycol in the electroplating solution is 50 mg / L to 200 mg / L. In some embodiments, the concentration of polyethylene glycol in the electroplating solution is 60 mg / L to 150 mg / L. In some embodiments, the concentration of polyethylene glycol in the electroplating solution is 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 100 mg / L, 150 mg / L, or 200 mg / L, or lies within any range between any two of the above values, or is any value within these ranges.

[0185] For polyethylene glycol, a molecular mass can be selected that is commonly used in the field of copper foils, for example polyethylene glycol with a relative molecular mass of 4000.

[0186] In some embodiments, the concentration of hydroxyethylcellulose in the electroplating solution is 30 mg / L to 200 mg / L. In some embodiments, the concentration of hydroxyethylcellulose in the electroplating solution is 50 mg / L to 150 mg / L. In some embodiments, the concentration of hydroxyethylcellulose in the electroplating solution is 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, 80 mg / L, 90 mg / L, 100 mg / L, 120 mg / L, 140 mg / L, 160 mg / L, 180 mg / L, or 200 mg / L, or lies within a range between any two of the above values ​​or is any value within these ranges.

[0187] For hydroxyethylcellulose, a molecular weight can be selected that is commonly used in the field of copper foils. In some embodiments, the relative molecular weight of the hydroxyethylcellulose is 120,000.

[0188] In some embodiments, the mass ratio of polyethylene glycol to hydroxyethylcellulose in the electroplating solution is (1 - 1.5) : 1. In some embodiments, the mass ratio of polyethylene glycol to hydroxyethylcellulose in the electroplating solution is (1.2 - 1.5) : 1. For example, the mass ratio of polyethylene glycol to hydroxyethylcellulose is 1 : 1, 1.1 : 1, 1.2 : 1, 1.3 : 1, 1.4 : 1 or 1.5 : 1, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0189] In some embodiments, the glazing agent comprises bis(sodium sulfopropyl)disulfide.

[0190] Without being bound to any specific theory, bis(sodium sulfopropyl)disulfide is adsorbed onto the cathode copper surface via thiol functional groups or disulfide bonds. The terminal sulfonate anions capture hydrated copper ions from the electroplating solution, thereby disrupting their hydration and interacting with the chloride ions adsorbed onto the cathode surface. This results in the transfer of electrons from the chloride ions to the captured copper ions. Consequently, the electrochemical reduction rate of the copper ions is significantly improved, the crystal grains are refined, and the material is strengthened.

[0191] In some embodiments, the concentration of bis(sodium sulfopropyl)disulfide in the electroplating solution is 500 mg / L to 2000 mg / L. In some embodiments, the concentration of bis(sodium sulfopropyl)disulfide in the electroplating solution is 500 mg / L to 1000 mg / L. In some embodiments, the concentration of bis(sodium sulfopropyl)disulfide in the electroplating solution is 500 mg / L, 600 mg / L, 700 mg / L, 800 mg / L, 900 mg / L, 1000 mg / L, 1500 mg / L, or 2000 mg / L, or lies within any range between any two of the above values ​​or is any value within these ranges.

[0192] In some embodiments, the electroplating solution comprises chloride ions, wherein the concentration of chloride ions (calculated as chlorine atoms) is 20 mg / L to 80 mg / L. In some embodiments, the concentration of bis(sodium sulfopropyl) disulfide in the electroplating solution is 40 mg / L to 80 mg / L. In some embodiments, the concentration of chloride ions (calculated as chlorine atoms) is 20 mg / L, 30 mg / L, 40 mg / L, 50 mg / L, 60 mg / L, 70 mg / L, or 80 mg / L, or lies within any range between any two of the above values ​​or is any value within these ranges. The combination of chloride ions with the wetting agent can further improve the electroplating process.

[0193] In some embodiments, the electroplating solution comprises: collagen with a concentration of 60 mg / L to 300 mg / L, sodium saccharin with a concentration of 0.5 g / L to 10 g / L, polyethylene glycol with a concentration of 50 mg / L to 200 mg / L, hydroxyethylcellulose with a concentration of 30 mg / L to 200 mg / L, bis-(sodium sulfopropyl)disulfide with a concentration of 500 mg / L to 2000 mg / L, and chloride ions with a concentration of 20 mg / L to 80 mg / L.

[0194] In some embodiments, the electroplating solution comprises: collagen with a concentration of 80 mg / L to 150 mg / L, sodium saccharin with a concentration of 0.5 g / L to 4 g / L, polyethylene glycol with a concentration of 60 mg / L to 150 mg / L, hydroxyethylcellulose with a concentration of 50 mg / L to 150 mg / L, bis-(sodium sulfopropyl)disulfide with a concentration of 500 mg / L to 1000 mg / L, and chloride ions with a concentration of 40 mg / L to 80 mg / L.

[0195] The electroplating solution also includes a copper source to supply the solution with copper ions. The electroplating solution further includes sulfuric acid to provide an acidic environment for the reduction of copper ions.

[0196] In some embodiments, the concentration of copper ions (calculated as copper atoms) is 60 g / L to 100 g / L. In some embodiments, the concentration of copper ions (calculated as copper atoms) is 80 g / L to 100 g / L. In some embodiments, the concentration of copper ions (calculated as copper atoms) is 60 g / L, 70 g / L, 80 g / L, 90 g / L, or 100 g / L, lies within any range between any two of the above values, or is any value within these ranges.

[0197] In some embodiments, the concentration of sulfuric acid is 60 g / L to 110 g / L. In some embodiments, the concentration of sulfuric acid is 80 g / L to 110 g / L. In some embodiments, the concentration of sulfuric acid is 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, or 110 g / L, lies within a range between any two of the above values, or is any value within these ranges.

[0198] In some embodiments, the pH value of the electroplating solution is 2.5 to 4.5, for example 2.5, 3.0, 3.5, 4.0 or 4.5, or lies in a range between any two of the above values ​​or is any value within these ranges.

[0199] The synergistic effect of the electroplating solution and parameters contributes to the formation of a copper foil with a heterogeneous crystal grain morphology and varying particle sizes. This copper foil exhibits excellent tensile strength and elongation at break, positively impacting the safety performance of high-energy-density or high-expansion batteries. Simultaneously, the manufacturing process enables large-scale production and offers promising prospects for industrial applications. [Negative electrode sheet]

[0200] As an example of the negative electrode sheet, the negative electrode current collector has two opposing surfaces in its own thickness direction, with the negative electrode film layer being arranged on one or both of these opposing surfaces of the negative electrode current collector.

[0201] In some embodiments, the negative electrode current collector can be the current collector described in the first aspect of the present application, which provides a material basis for improving the energy density of the secondary battery and contributes to improving the safety of the secondary battery.

[0202] 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, lithium titanate, and lithium metal. The tin-based material may comprise one or more of elemental tin, tin oxide, and tin alloy.

[0203] In some embodiments, the negative electrode active material comprises a silicon-based material, and the silicon-based material comprises one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy.

[0204] 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%.

[0205] 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 80%.

[0206] 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 30%.

[0207] 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%, 100%, or lies in a range between any two of the above values.

[0208] In some embodiments, the mass fraction of the element silicon in the silicon-based material is 20% to 50%.

[0209] In some embodiments, the mass fraction of the element silicon in the silicon-based material is 20%, 25%, 30%, 35%, 40%, 45%, 50%, or lies in a range between any two of the above values.

[0210] In some embodiments, the mass fraction of the element silicon, based on the total mass of the negative electrode film layer, is 4% to 10%.

[0211] In some embodiments, the mass fraction of the element silicon, based on the total mass of the negative electrode film layer, is 4%, 5%, 6%, 7%, 8%, 9%, 10%, or lies in a range between any two of the above values.

[0212] In some embodiments, the negative electrode film layer optionally comprises a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0213] In some embodiments, the negative electrode sheet further comprises a conductive material. The conductive material comprises one or more of superconducting carbon, carbon black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0214] In some embodiments, the conductive material comprises carbon black. In some embodiments, the conductive material comprises carbon nanotubes. In some embodiments, the conductive material comprises both carbon black and carbon nanotubes. The conductive material is widely available and possesses excellent conductivity properties, which positively impacts the control of the secondary battery's manufacturing costs and the improvement of the conductivity properties of the negative electrode sheet.

[0215] In some embodiments, the negative electrode film layer may optionally also include other excipients, such as a thickening agent (such as sodium carboxymethylcellulose (CMC-Na)).

[0216] In some embodiments, the negative electrode sheet can be produced as follows: The above-mentioned components for producing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode paste; the negative electrode paste is used to coat the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet can be obtained. [Positive electrode sheet]

[0217] 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, and the positive electrode film layer comprises a positive electrode active material.

[0218] As an example, the positive electrode current collector has two opposing surfaces in its own thickness direction, with the positive electrode film layer being arranged on one or both of the two opposing surfaces of the positive electrode current collector.

[0219] In some embodiments, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector can comprise a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on the polymer material substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0220] In some embodiments, the positive electrode active material can be a positive electrode active material known in the art for a battery. For example, the positive electrode active material can comprise at least one lithium-containing phosphate with an olivine structure, lithium transition metal oxide, and their modified compounds. However, the present application is not limited to these materials, and other conventional materials suitable for use as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone or in combination with one or more of them.Examples of lithium transition metal oxides include at least one of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (such as LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 (designated), LiNi 0,5 Co 0,2 Mn 0,3 O2 (also known as NCM) 523 (designated), LiNi 0,5 Co 0,25 Mn 0,25 O2 (also known as NCM) 211 (designated), LiNi 0,6 Co 0,2 Mn 0,2 O2 (also known as NCM) 622 (designated), LiNi 0,8 Co 0,1 Mn 0,1 O2 (also known as NCM) 811 lithium nickel cobalt aluminum oxide (such as LiNi) 0,85 Co 0,15 Al 0,05Examples of lithium-containing phosphate with an olivine structure may include, but are not limited to, at least one of the following: lithium iron phosphate (such as LiFePO4 (also known as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, or lithium manganese iron phosphate and carbon composites.

[0221] In some embodiments, the positive electrode film layer optionally comprises a binder. For example, the binder may comprise at least one of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0222] In some embodiments, the positive electrode film layer optionally further comprises a conductive material. For example, the conductive material may comprise at least one of superconducting carbon, carbon black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0223] In some embodiments, the positive electrode sheet can be produced as follows: The above-mentioned components for producing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, are dispersed in a solvent (such as N-methyl-2-pyrrolidone) to form a positive electrode paste; the positive electrode current collector is coated with the positive electrode paste, and after drying, cold pressing, and other processes, the positive electrode sheet can be obtained. [Electrolyte]

[0224] The electrolyte serves to conduct ions between the positive and negative electrode sheets. This application does not impose any specific restrictions regarding the type of electrolyte, and the type can be selected according to the requirements. For example, the electrolyte can be liquid, gel-like, or completely solid.

[0225] In some embodiments, the electrolyte is in the form of an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent.

[0226] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, lithium difluorobisoxalatophosphate and lithium tetrafluoro(oxalato)phosphate.

[0227] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0228] In some embodiments, the electrolyte solution optionally includes an additive. For example, the additive may include an additive for negative electrode film formation, an additive for positive electrode film formation, and an additive that can improve certain battery performance characteristics, such as an additive that improves the battery's overcharge behavior, an additive that improves the battery's high-temperature performance, and an additive that improves the battery's low-temperature performance. [Separator]

[0229] In some embodiments, the secondary battery also includes a separator. The present application does not impose any specific restrictions on the type of separator, and any known separator with good chemical and mechanical stability and a porous structure can be used.

[0230] In some embodiments, the separator material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film without any particular restriction. If the separator is a multi-layer composite film, the materials of each layer can be the same or different without any particular restriction.

[0231] In some embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode arrangement by a winding or stacking process.

[0232] 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.

[0233] In some embodiments, the outer packaging of the secondary battery can be a rigid casing, such as a hard plastic casing, an aluminum casing, a steel casing, etc. The outer packaging of the secondary battery can also be a soft casing, such as a bag-like soft casing. The material of the soft casing can be plastic. Examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0234] In some embodiments, the secondary battery comprises a wound secondary battery, and the positive electrode sheet, the negative electrode sheet and the separator are formed into an electrode arrangement by a winding process.

[0235] In some embodiments, the secondary battery comprises a stacked secondary battery, and the positive electrode sheet, the negative electrode sheet and the separator are formed into an electrode arrangement by a stacking process.

[0236] Furthermore, the secondary battery, the battery module, the battery pack and the power-consuming device of the present application will be described below, where appropriate with reference to the drawings.

[0237] In one embodiment of the present application, a secondary battery is provided.

[0238] The present application does not impose any special restrictions regarding the shape of the secondary battery; it can be cylindrical, rectangular, or any other shape. For example, shows Fig. 1 as an example a secondary battery 5 with a square structure.

[0239] In some embodiments, the outer packaging, referring to Fig.2, comprising a housing body 51 and a cover plate 53. The housing body 51 may comprise 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 may cover the opening to close the receiving chamber. The positive electrode sheet, the negative electrode sheet, and the separator may be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is enclosed in the receiving chamber. The electrolyte solution is impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more; the person skilled in the art may choose according to specific actual requirements.

[0240] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The exact number can be selected by a person skilled in the art depending on the application and capacity of the battery module.

[0241] Fig. Figure 3 shows an example of a battery module 4. Referring to Fig. 3. Several secondary batteries 5 can be arranged one after the other in the battery module 4 along its length. Of course, other arrangements are also possible. Furthermore, the multiple secondary batteries 5 can be secured by fastening elements.

[0242] Optionally, the battery module 4 can also include a housing with a receiving space, in which the multiple secondary batteries 5 are received.

[0243] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, wherein the number of battery modules contained in the battery pack can be one or more; the person skilled in the art can select a specific number depending on the application and capacity of the battery pack.

[0244] The Fig. 4 and Fig. Figure 5 shows, as an example, a battery pack 1. Referring to the Fig. 4 and Fig. 5. The battery pack 1 can comprise a battery box and several battery modules 4 arranged therein. 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 receiving the battery modules 4. The multiple battery modules 4 can be arranged in any way within the battery box.

[0245] Furthermore, the present application provides a power-consuming device comprising at least one of the secondary batteries, battery modules, or battery packs 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 devices can include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0246] The secondary battery, battery module or battery pack can be selected as needed for the power-consuming device.

[0247] Fig. Figure 6 shows an example of a power-consuming device. This 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 of the secondary battery, a battery pack or battery module can be used.

[0248] As another example, the device could be a mobile phone, a tablet, a laptop, etc. The device typically needs to be lightweight and thin and can use a secondary battery as a power source. Example of implementation

[0249] The following are exemplary embodiments of the present application. These embodiments are for illustrative purposes only and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the technical literature or product instructions must be followed. All reagents and instruments used without manufacturer information are commercially available products. I. Performance tests(1) Examination of the characteristics of the crystal grains of the copper foil

[0250] Scanning electron microscopy using electron backscatter diffraction (EBSD) is employed to observe the cross-section of the copper foil, with the Oxford C-Nano+ electron backscatter diffraction apparatus being used. An inverse pole figure distribution diagram (magnification: 3000x) is obtained. The particle sizes of the individual crystal grains are measured. The diameter of the equivalent circle of the crystal grains is used as the particle size of the crystal grains, and a statistical analysis of the particle size distribution of the crystal grains is performed, which is fitted using a skewness distribution.Then, a total number of copper crystal grains, an average particle size, a maximum particle size, a minimum particle size, a particle size range, a proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm, and a proportion of the number of copper crystal grains with a particle size greater than 0.5 µm are determined. (2) Testing of mechanical properties

[0251] According to GB / T 5230-1995 "Electrolytic copper foil", the copper foils produced in the exemplary embodiments are cut into tensile specimens with a length L0 of 50 mm and a width of 15 mm. The tensile strength test is carried out using a universal testing machine at 25 °C and a tensile speed of 50 mm / min.

[0252] Then the cross-sectional area S0 of the Tensile test=mρ×L0, where ρ is 8.96 g / cm³ 3 is, m is in grams and L0 is in centimeters.

[0253] The specimen is continuously loaded until it breaks. The maximum load F is read either from the force gauge or from the tensile force-strain curve. The tensile strength σ b is calculated according to Formula I. σb=FS0

[0254] The distance between the two lines after the specimen fractures is denoted as L1, which is measured on the specimen or read from the tensile force-strain curve. L1 can be determined using the straight line method or the displacement method, and the elongation at break δ is calculated according to Formula II. δ=L1−L0L0 (3) Hardness test

[0255] A copper foil sample is placed in a metallographic hot-mounting machine, then wood glue powder is poured in and heated at a rate of 150 °C for 10 minutes. The sample is then loaded with a rhombic indenter of the Vickers hardness tester (50 g weight), and the lengths of the two diagonals are measured optically. The corresponding Vickers hardness is determined according to the following formula. HV=0.102×2F sinα2d2 HV stands for Vickers hardness; F represents the load on the intruder head (Newton force); α represents the angle between the indenter head and the surface (136°); d represents the average length of the diagonal lines (mm). (4) State of Health (SOH) corresponding to crack failure

[0256] At 25 °C, the battery is charged to 3.8 V at a constant current of 1 C, then charged to a current ≤ 0.05 C at a constant voltage of 3.8 V, and subsequently discharged to 2.5 V at a constant current of 1 C – this constitutes one charge and discharge cycle. The charge and discharge cycle is repeated. The state of health (SOH) of the cell is monitored throughout the entire process. Subsequently, a computed tomography (CT) scan of the cell is performed at every 1% change in SOH to detect internal cracks. If cracks are present, the battery is disassembled after crack failure to check if the negative electrode sheet is fractured. This determines the SOH corresponding to the crack failure. (5) Testing of the thickness expansion rate and expansion force of the secondary battery in case of crack failure:

[0257] First, the total thickness H0' of the secondary battery is measured at 25 °C. The battery is then charged to 3.8 V at a constant current of 1 C, then charged to a current ≤ 0.05 C at a constant voltage of 3.8 V, and finally discharged to 2.5 V at a constant current of 1 C – this constitutes a charge and discharge cycle. The charge and discharge cycle is repeated. The state of health (SOH) of the cell is monitored throughout the entire process. Subsequently, a computed tomography (CT) scan of the cell is performed at every 1% change in SOH to detect internal cracks. If cracks are present, the battery is disassembled after crack failure to check if the negative electrode sheet is fractured. This determines the SOH value corresponding to the crack failure.The total thickness H1' of the secondary battery is measured at this point, and the rate of thickness expansion is calculated using the formula (H1' - H0') / H0'. Simultaneously, the expansion force is measured using pressure sensors located in the clamping device on both sides of the large surfaces of the electrode sheet of the secondary battery cell. (6) Testing the rate of thickness expansion and expansion force of the secondary battery at 60% SOH:

[0258] First, the total thickness of the secondary battery is measured at 25 °C. The battery is then charged to 3.8 V at a constant current of 1 C, then charged to a current ≤ 0.05 C at a constant voltage of 3.8 V, and finally discharged to 2.5 V at a constant current of 1 C – this constitutes a charge and discharge cycle. The charge and discharge cycle is repeated. The state of health (SOH) of the cell is monitored throughout the entire process until the battery reaches 60% SOH. The expansion force at this point is measured using pressure sensors located in the clamping device on both sides of the large surfaces of the electrode sheet of the secondary battery cell. Additionally, the total thickness of the secondary battery is measured, and the rate of thickness expansion at 60% SOH is calculated using the formula (current thickness - total thickness at initial state) / total thickness at initial state. II. Manufacturing Method Example 1(1) Production of the copper foil

[0259] A copper plate or wire with a purity of at least 99.9% was dissolved in sulfuric acid with a mass fraction of 98% to obtain a copper sulfate solution, which served as the copper source. At 55 °C, additives and hydrochloric acid were added to prepare an electroplating solution. The concentrations of collagen (with a relative molecular mass of 8000 to 12000) were 120 mg / L, polyethylene glycol (with a relative molecular mass of 4000) 80 mg / L, hydroxyethylcellulose (with a relative molecular mass of approximately 120000) 60 mg / L, chloride ions 40 mg / L, bis(sodium sulfopropyl) disulfide 600 mg / L, sodium saccharin 2 g / L, copper ions (calculated as copper atoms) 90 g / L, and the remainder was deionized water. The pH value of the electroplating solution was 3.5.

[0260] A sinusoidal pulsed current was periodically applied to the polished titanium cathode roller, with the anode electrode being a titanium substrate plate. The surface area of ​​the titanium roller immersed in the electroplating solution was 8.67 m². 2 The rotational speed (rolling speed) of the titanium roller was 2.4 m / min. The applied sinusoidal pulse current had a peak current of 55,000 A, a trough current of 2,500 A, and a period of 3,000 ms. The cathode-anode distance was 10 mm. At a deposition temperature of 55 °C, a copper foil with a thickness of 6 µm was deposited onto the titanium roller. (2) Battery production

[0261] 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.

[0262] Silicon carbon (with a silicon content of 20 wt.% to 50 wt.%) and synthetic graphite, acetylene carbon black as a conductive agent, styrene-butadiene rubber (SBR) as a binder, and sodium carboxymethylcellulose (CMC-Na) as a thickener were dissolved and uniformly mixed in demineralized water in a weight ratio of 20 : 76 : 1 : 1.5 : 1.5 to produce a negative electrode paste; then the copper foil of the negative electrode current collector was uniformly coated once or several times with the negative electrode paste, and after drying, cold pressing, and cutting, a negative electrode sheet was obtained, with the capacitance per gram of negative electrode active material in the negative electrode film layer being 800 mAg / h to 1500 mAg / h.

[0263] In an argon atmosphere glovebox (H₂O < 0.1 ppm, O₂ < 0.1 ppm), ethylene carbonate, diethyl carbonate, and dimethyl carbonate were mixed in a 1:1:1 volume ratio, and LiPF₆ was dissolved in the above solution to obtain an electrolyte solution. The concentration of LiPF₆ in this electrolyte solution was 1 mol / L. 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.

[0264] Polypropylene film is used as a separator.

[0265] 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. Example 2-3

[0266] The manufacturing process of embodiment 2-3 was basically the same as that of embodiment 1, but the composition of the electroplating solution (see Table 1) and the parameters of the sinusoidal pulse current (see Table 2) were adapted; the thickness of the deposited copper foil was 6 µm. Comparison example 1-2

[0267] The manufacturing process of Comparative Example 1 was basically the same as that of Exemplary Example 1, however, a direct current was used for deposition and the deposition current was 55000 A. The thickness of the copper foil was 6 µm.

[0268] The manufacturing process of Comparative Example 2 was essentially the same as that of Exemplary Example 1, except that a DC deposition current of 30,000 A was used. The thickness of the copper foil was 6 µm. Table 1: Composition of the electroplating solution group Leveling agent wetting agent Glossing agent Chloride ions (mg / L) Copper ions (g / L) pH Collagen (mg / L) Sodium saccharin (g / L) Polyethylene glycol (mg / L) Hydroxyethylcellulose (mg / L) Bis-(sodium sulfopropyl) disulfide (mg / L) Example 1 120 2 80 60 600 40 90 3,5 Example 2 120 2 120 100 600 60 90 3,5 Example 3 120 2 120 100 600 60 90 3,5 Comparative example 1 120 2 80 60 600 40 90 3,5 Comparative example 2 120 2 80 60 600 40 90 3,5 Table 2: Parameters of the sinusoidal pulse current group Peak current (A) Valley Stream (A) Period (ms) Example 1 55000 2500 3000 Example 2 65000 2500 3000 Example 3 65000 5000 3000 Comparative example 1 55000 N / A N / A Comparative example 2 30000 N / A N / A NA means "not applicable".

[0269] The crystal grain characteristics and mechanical properties of the copper foils produced in embodiments 1 to 3 and comparative examples 1 to 2, as well as the results of the secondary batteries, are listed in the following Table 3.

[0270] The Fig. 7, Fig. 10 and Fig. Figure 13 shows the inverse pole figure distribution diagrams of the copper foil cross-sections of embodiments 1 to 3, which were tested by EBSD, where T runs along the thickness direction of the current collector and the copper foil cross-section has a heterogeneous crystal grain structure with a mixed distribution of large and small crystal grains. In comparison to the inverse pole figure distribution diagram of the copper foil of comparison example 2 ( Fig. 17) can be seen that in the copper foils of embodiments 1 to 3 more fine crystal grains are distributed and the particle size of the crystal grains is smaller overall.

[0271] The Fig. 9, Fig. 12, Fig. 15 and Fig.Figure 19 shows the diagrams for the particle size distribution of the copper foils of embodiments 1 to 3 and of comparative example 2. Table 3 shows that in the copper foils of embodiments 1 to 3, the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm is in the range of 70% to 95%, especially in the range of 80% to 95%, whereas the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm in comparative example 2 is less than 50%, which indicates that the copper crystal grains of embodiments 1 to 3 are generally finer and the copper foils have a higher mechanical strength.Furthermore, in the copper foils of embodiments 1 to 3, the proportion of copper crystal grains with a particle size greater than 0.5 µm ranges from 5% to 30%, while in comparative example 2, the proportion of copper crystal grains with a particle size greater than 0.5 µm is 50.5%. The copper foils of embodiments 1 to 3 exhibit plasticity comparable to that of the copper foil of comparative example 2. This suggests that the production of copper foils using a sinusoidal pulse current contributes to adjusting the particle size distribution of the copper crystal grains and thus improves the mechanical properties and plasticity of the copper foils.

[0272] In the copper foils of embodiments 1 to 3, the average particle size is in the range of 0.3 µm to 0.6 µm, the maximum particle size is in the range of 1 µm to 2 µm, the minimum particle size is in the range of 0.1 µm to 0.3 µm, and the particle size range is 0.8 µm to 2 µm. In comparative example 2, the range of particle sizes of the copper crystal grains is larger, and the average particle size of the copper crystal grains is larger. It is understandable that the copper foils of embodiments 1 to 3 exhibit a higher density accumulation at crystal interfaces and higher mechanical strength; the copper foil of comparative example 2 exhibits lower density accumulation at crystal interfaces and lower mechanical strength. The same applies to the tensile strength of embodiments 1 to 3 and comparative example 2.

[0273] The Fig. 8, Fig. 11 and Fig.Figure 14 shows the tensile strength-strain curves of the copper foils of embodiments 1 to 3. It can be seen that the tensile strength of the produced copper foils is in the range of 600 MPa to 1000 MPa and the elongation at break of the copper foils is in the range of 4% to 8% (Table 3). This indicates that the copper foils exhibit excellent strength and plasticity. Fig. Figure 16 shows the tensile strength-strain curve of the copper foil of comparative example 1. The tensile strength of the copper foil is similar to that of embodiment 1, but the elongation at break is only 2.7%, which indicates poor plasticity. Fig. Figure 18 shows the tensile force-strain curve of the copper foil of comparative example 1. The elongation at break of the copper foil is similar to that of embodiment 1, but the tensile strength is low.

[0274] The hardness of the copper foils of embodiments 1 to 3 is in the range of 55 HV to 65 HV, which indicates that the copper foils have good compression set and puncture resistance.

[0275] Comparative Example 1 uses a direct current with the same peak current as embodiment 1 to produce the copper foil. In comparison with embodiment 1, it is evident that the copper foil of Comparative Example 1 has a similar tensile strength and hardness to the copper foil of embodiment 1, but the elongation at break is significantly lower. This shows that the particle size distribution of the copper crystal grains can be adjusted by the sinusoidal pulse current and the current parameters, so that the copper foil can exhibit excellent plasticity combined with good mechanical strength.

[0276] Compared to Comparative Examples 1 and 2, the SOH corresponding to the crack failure of embodiments 1 to 3 is significantly reduced, indicating that the copper foils produced in embodiments 1 to 3 considerably improve the service life and safety of the secondary battery. Although the copper foil of Comparative Example 2 exhibits excellent elongation at break, its tensile strength is relatively low, resulting in a relatively high SOH value corresponding to crack failure. In contrast, the tensile strength of the copper foils produced in embodiments 1 to 3 using sinusoidal pulse current with varying current intensity is significantly improved, while maintaining good plasticity. The SOH value corresponding to crack failure is significantly reduced, which can improve the cell's service life by more than 25% SOH.

[0277] In comparison to examples 1 and 2, the copper foils of embodiments 1 to 3 exhibit good mechanical properties and plasticity and can effectively reduce the probability of current collector cracks or fractures due to secondary battery expansion. For secondary batteries with high expansion properties, exhibiting an expansion force greater than or equal to 1000 kgf and a thickness expansion rate of 4% to 10%, the copper foils of embodiments 1 to 3 can effectively reduce the probability of current collector cracks or fractures, thereby reducing the state of health (SOH) of the secondary battery upon crack failure (i.e., effectively improving the service life and safety of the secondary battery) and decreasing the probability of secondary battery failures and performance losses due to battery expansion.

[0278] 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 all included within the technical scope of the present application. 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 patent literature

[0000] CN 202411154807.0

[0001] Cited non-patent literature

[0000] Standard GB / T 5230-1995 “Electrolytic copper foil

[0127] According to GB / T 5230-1995 “Electrolytic copper foil

[0251]

Claims

[1] Secondary battery, characterized by , that it comprises a copper foil, wherein the copper foil comprises copper crystal grains of different particle sizes, wherein the copper crystal grains comprise copper crystal grains with a particle size of less than or equal to 0.5 µm and copper crystal grains with a particle size greater than 0.5 µm, wherein the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm to the total number of copper crystal grains is 70% to 95%, and the proportion of the number of copper crystal grains with a particle size greater than 0.5 µm to the total number of copper crystal grains is 5% to 30%. [2] Secondary battery according to claim 1, characterized by , that the particle size range of the copper crystal grains is greater than 0.5 µm and less than or equal to 3 µm. [3] Secondary battery according to claim 1 or 2, characterized by, that the proportion of the number of copper crystal grains with a particle size of less than or equal to 0.5 µm in the total number of copper crystal grains is 80% to 95%, and / or the proportion of the number of copper crystal grains with a particle size of greater than 0.5 µm in the total number of copper crystal grains is 5% to 20%. [4] Secondary battery according to any one of claims 1 to 3, characterized by that the copper foil meets at least one of the following conditions: (1) the average particle size of the copper crystal grains is 0.3 µm to 1.2 µm; (2) the maximum particle size of the copper crystal grains is 1 µm to 2.5 µm; (3) the minimum particle size of the copper crystal grains is 0.1 µm to 0.3 µm; (4) the particle size range of the copper crystal grains is 0.8 µm to 2.5 µm. [5] Secondary battery according to any one of claims 1 to 4, characterized bythat the copper foil meets at least one of the following conditions: (1) the average particle size of the copper crystal grains is 0.3 µm to 0.6 µm; (2) the maximum particle size of the copper crystal grains is 1.2 µm to 2.0 µm; (3) the minimum particle size of the copper crystal grains is 0.1 µm to 0.3 µm; (4) the particle size range of the copper crystal grains is 1 µm to 2 µm. [6] Secondary battery according to any one of claims 1 to 5, characterized by , that under test conditions of room temperature (20 ± 10 °C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min the tensile strength of the copper foil is 600 MPa to 1000 MPa, and / or the elongation at break of the copper foil is 4 % to 8 %. [7] Secondary battery according to any one of claims 1 to 6, characterized by, that under test conditions of room temperature (20 ± 10 °C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min the tensile strength of the copper foil is 700 MPa to 1000 MPa, and / or the elongation at break of the copper foil is 4 % to 7 %. [8] Secondary battery according to any one of claims 1 to 7, characterized by , that under test conditions of room temperature (20 ± 10 °C), a sample length × width of (50 ± 0.25 mm) × (15 ± 0.25 mm) and a tensile speed of 50 ± 0.5 mm / min the tensile strength of the copper foil is 700 MPa to 800 MPa, and / or the elongation at break of the copper foil is 5 % to 6 %. [9] Secondary battery according to any one of claims 1 to 8, characterized by that the hardness of the copper foil is 55 HV to 65 HV. [10] Secondary battery according to any one of claims 1 to 9, characterized by that the hardness of the copper foil is 55 HV to 60 HV. [11] Secondary battery according to any one of claims 1 to 10, characterized by , that the thickness of the copper foil is 4 µm to 10 µm. [12] Secondary battery according to any one of claims 1 to 11, characterized by , that the secondary battery further comprises a negative electrode film layer located on at least one side of the copper foil, wherein a negative electrode active material in the negative electrode film layer comprises at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material and lithium titanate. [13] Secondary battery according to claim 12, characterized by , that the negative electrode active material comprises a silicon-based material, wherein the silicon-based material comprises at least one of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite and silicon alloy. [14] Power-consuming device, characterized by , that it comprises a secondary battery according to claims 1 to 13.

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