Copper foil and preparation method thereof, and current collector, pole piece, lithium secondary battery and energy storage device containing copper foil

Abstract

The invention provides a copper foil and a preparation method thereof, and a current collector, a pole piece, a lithium secondary battery and an energy storage device containing the copper foil. The tensile strength, thickness and grain parameters of the copper foil meet the following relations: UHT is the tensile strength, and the unit is MPa; delta is the number of twin crystal grains in a 5.5 [mu] m * 26 [mu] m rectangular area of the cross section of the copper foil; m is the maximum value of the grain fitting ellipse diameter in the rectangular area, and the unit is mu m; n is the minimum value of the grain fitting ellipse diameter in the rectangular area, and the unit is mu m; the average value is the average value of grain fitting ellipse diameters in the rectangular area, and the unit is mu m; rho is the thickness of the copper foil, and the unit is [mu] m. According to the copper foil, the weight of the battery is reduced, and the energy density of the battery is improved; meanwhile, the mechanical strength is greater than or equal to 700MPa; and interface stripping caused by deformation or yield of the current collector can be reduced.

Description

Technical Field

[0001] This invention relates to a copper foil and its preparation method, as well as current collectors, electrodes, lithium batteries, and energy storage devices containing the copper foil, belonging to the field of electrolytic copper foil. Background Technology

[0002] Energy storage devices (including energy storage batteries and supercapacitors) have important applications in various consumer electronics, electric vehicles, and grid storage due to their advantages such as high energy density, high specific energy, lightweight, and long cycle life. The market share of lithium-ion batteries, their main representative, is constantly increasing. However, further development of these batteries is still needed to meet the more demanding application conditions in fields such as all-electric vehicles, drones, consumer electronics, high-efficiency cargo ships and aircraft, aerospace applications, and power grids.

[0003] Currently, graphite is the mainstream anode material for rechargeable lithium-ion batteries because it can provide reversible lithium-ion insertion channels and exhibit morphological and volume changes of less than 10%. However, with the development of lithium-ion batteries, its relatively low specific capacity (370 mAh / g) increasingly restricts the improvement of lithium-ion battery capacity. Silicon materials, on the other hand, possess high theoretical specific capacity (4200 mAh / g) and ideal operating potential (<0.5V vs Li / Li). + Furthermore, silicon is abundant in natural reserves and is considered an ideal alternative material for lithium-ion battery anodes. To date, the commercial application of silicon has primarily been in the form of silicon-carbon or silicon-oxygen anodes, making the complete application of silicon-based electrodes very difficult. On one hand, Li-Si electrodes undergo significant crushing and delamination during lithiation, and suffer from unstable electrolyte interfaces. The breakage of active silicon material significantly shortens the cycle life of lithium-ion batteries, and damaged material can puncture the separator, causing short circuits between the positive and negative electrodes and posing a risk of thermal runaway. On the other hand, silicon anode materials exhibit extreme volume changes during charge-discharge cycles, reaching up to 300%. Such volume changes not only easily cause delamination between the silicon anode and the current collector, preventing electron transfer and rendering silicon particles ineffective, thus reducing the overall battery capacity; but also easily create stress concentration areas on the electrode, causing stress fatigue in the current collector in these areas, leading to microcracks or even breakage, affecting battery capacity and cycle life.

[0004] To improve the performance and applications of silicon anode materials, two main approaches are taken: First, by designing the composition and structure of silicon-based materials, such as reducing the size of active materials to the nanoscale to improve their stability; or by thinning the active materials to achieve a larger specific surface area to thickness ratio; or by utilizing the synergistic effect between the components of composite materials to achieve complementary advantages; or even by designing silicon-based materials into porous structures to improve electrolyte wetting while also providing space for silicon expansion; Second, by developing current collectors with superior performance, such as those with ultra-high tensile strength and excellent elongation, which can effectively resist the stress generated by the expansion and contraction of silicon-based materials, thus adapting them to applications.

[0005] Nanoscale silicon-based active materials can alleviate the volume effect of alloy materials to some extent, but the ultra-fine size structure has more surface films and introduces more oxide impurities, reducing the first cycle efficiency of the cell. Thin-film active materials are more prone to breakage and shedding during cycling, resulting in cell capacity loss and increased safety risks. Composite active materials contain inert materials that occupy a certain volume and mass, which weakens the battery's energy density. Porous silicon-based materials have the problem of continuous damage and repair of the SEI film during cycling, and the expansion and contraction of silicon will push away the surrounding binders, resulting in a significant decrease in cell cycle life and energy density. Summary of the Invention

[0006] The problem the invention aims to solve

[0007] To address the problems arising from using silicon as the negative electrode material, there is an urgent need for a copper foil with high mechanical strength, thinness, and light weight. This invention provides a copper foil and its preparation method, as well as a current collector, electrode, lithium secondary battery, and energy storage device incorporating the copper foil. The copper foil of this invention is thin, lightweight, and possesses sufficient mechanical strength to withstand the volume changes of silicon material during charging and discharging.

[0008] Solution for solving the problem

[0009] This invention provides a copper foil, wherein the tensile strength, thickness, and grain parameters of the copper foil satisfy the following relationship:

[0010]

[0011] Wherein, UHT represents tensile strength, in MPa;

[0012] δ represents the number of twin grains within a rectangular area of ​​5.5μm × 26μm in the copper foil cross-section;

[0013] m is the maximum value of the fitted ellipse diameter of the grains within the rectangular area, in μm;

[0014] n is the minimum diameter of the fitted ellipse of the grains within the rectangular area, in μm;

[0015] The average diameter of the fitted ellipse within the rectangular area is given, in μm.

[0016] ρ represents the thickness of the copper foil, in μm.

[0017] According to the copper foil of the present invention, the ratio of twin grain region to twin grain ratio in the copper foil is 1.0-3.0.

[0018] The copper foil according to the present invention has a thickness ≤ 5 μm.

[0019] According to the copper foil of the present invention, the copper foil has a tensile strength ≥700MPa and an elongation at break ≥ρ-0.5 at room temperature, where ρ is the thickness of the copper foil in μm.

[0020] The present invention also provides a method for preparing copper foil according to the present invention, comprising the following steps:

[0021] Step 1) Prepare the electrolyte, which comprises the following components: copper ions 85-125 g / L, sulfuric acid 80-110 g / L, chloride ions 20-60 ppm, and agents A, B, and C.

[0022] Wherein, agent A is an organic divalent sulfur compound, agent B comprises polyether compounds and nitrogen-containing heterocyclic compounds, and agent C is a nitrogen-containing compound.

[0023] The total concentration of agents A, B, and C is 105-260 ppm, the concentration of agent C is 15 ppm-60 ppm, and the concentrations of agents A, B, and C satisfy the relationship: A / (B+C)=1.8-3.2;

[0024] Step 2) The electrolyte is used to prepare the copper foil by electrochemical deposition.

[0025] According to the preparation method of the present invention, one or more of the following (1)-(3) are satisfied:

[0026] (1) The A agent is selected from one or more of sodium dithiopropane sulfonate (SPS), sodium 3-mercapto-1-propane sulfonate, sodium thiopropane sulfonate (HP), and dimercaptosuccinic acid (DMSA), and the concentration of the A agent is 80ppm-150ppm;

[0027] (2) The agent B comprises a polyether compound and a nitrogen-containing heterocyclic compound. The polyether compound is selected from one or more of polyethylene glycol (PEG) with a molecular weight of 600-10000, polypropylene glycol (PPG) with a molecular weight of 400-2000, and polyethylene glycol-polypropylene glycol block copolymer. The nitrogen-containing heterocyclic compound is selected from one or two of polyvinylpyrrolidone (PVP) and polyvinylimidazole (PVI). The concentration of the agent B is 10-50 ppm.

[0028] (3) The agent C is selected from one or more of gelatin, collagen, polyethyleneimine (PEI) with a molecular weight of 600-100000, tetrahydrothiazothione, and chitosan derivatives.

[0029] The present invention also provides a current collector comprising the copper foil described herein.

[0030] The present invention also provides an electrode comprising the current collector described herein.

[0031] The present invention also provides a lithium secondary battery, comprising the electrode sheet described in the present invention.

[0032] The present invention also provides an energy storage device, including the lithium secondary battery described in the present invention.

[0033] The effects of the invention

[0034] The current collector using the copper foil of this invention has an extremely thin thickness and extremely high tensile strength. During the cell manufacturing process, it is less prone to deformation, wrinkling, or breakage, improving production efficiency. Simultaneously, it effectively resists the enormous tensile and compressive stresses generated by silicon expansion, avoiding the risk of electrode failure and internal short circuits due to copper foil tearing. The electrode sheet using the above-mentioned current collector exhibits higher adhesion between the copper foil substrate and silicon-based or other negative electrode active materials with higher coefficients of contraction and expansion, helping to maintain the integrity of the electrode structure. The conductive network between negative electrode active materials and between the active materials and the current collector reduces contact resistance, thereby enabling lithium secondary batteries using this electrode sheet to have high energy density, long cycle life, and high safety. Attached Figure Description

[0035] Figure 1 Backscatter diffraction (EBSD) pattern of copper foil-I obtained in Example 1;

[0036] Figure 2 Photograph of the negative electrode after disassembly of the battery cell prepared in Example 3 under full charge after cyclic testing;

[0037] Figure 3 Photograph of the negative electrode after disassembly of the battery cell prepared by Comparative Example 4 in a fully charged state following a cyclic test. Detailed Implementation

[0038] Various exemplary embodiments, features, and aspects of the present invention will be described in detail below. The term "exemplary" as used herein means "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as superior to or better than other embodiments.

[0039] Furthermore, to better illustrate the present invention, numerous specific details are set forth in the following detailed embodiments. Those skilled in the art should understand that the present invention can be practiced without certain specific details. In other instances, methods, means, apparatus, and steps well known to those skilled in the art have not been described in detail in order to highlight the spirit of the present invention.

[0040] Unless otherwise stated, all units used in this specification are international standard units, and all numerical values ​​and ranges appearing in this invention should be understood to include systematic errors that are unavoidable in industrial production.

[0041] In this specification, the word "may" has two meanings: to perform a certain process and not to perform a certain process.

[0042] In this specification, references to "some specific / preferred embodiments," "other specific / preferred embodiments," "implementation," etc., refer to specific elements (e.g., features, structures, properties, and / or characteristics) related to that embodiment, which are included in at least one of the embodiments described herein and may or may not be present in other embodiments. Furthermore, it should be understood that these elements may be combined in any suitable manner in various embodiments.

[0043] In this specification, the range of values ​​referred to as “value A - value B” is the range that includes the endpoint values ​​A and B.

[0044] [Copper foil]

[0045] This invention provides a copper foil, wherein the tensile strength, thickness, and grain parameters of the copper foil satisfy the following relationship:

[0046]

[0047] Wherein, UHT represents tensile strength, in MPa;

[0048] δ represents the number of twin grains within a rectangular area of ​​5.5μm × 26μm in the copper foil cross-section;

[0049] m is the maximum value of the fitted ellipse diameter of the grains within the rectangular area, in μm;

[0050] n is the minimum diameter of the fitted ellipse of the grains within the rectangular area, in μm;

[0051] The average diameter of the fitted ellipse within the rectangular area is given, in μm.

[0052] ρ represents the thickness of the copper foil, in μm.

[0053] The UHT, δ, m, n of the copper foil of the present invention The relationship between ρ and ρ is satisfied, breaking the paradox of "thinning inevitably sacrifices strength" in the traditional understanding. Through the three-dimensional synergistic gain of strength-thickness-grain structure, the mechanical strength of extremely thin copper foil is greatly improved.

[0054] According to the copper foil of the present invention, the ratio of twin grain region to twin grain ratio in the copper foil is 1.0-3.0, preferably 1.2-2.5, more preferably 1.7-2.0, and most preferably 1.75-1.95.

[0055] The copper foil according to the present invention has a thickness ≤ 5 μm.

[0056] According to the copper foil of the present invention, the copper foil has a tensile strength ≥700MPa and an elongation at break ≥ρ-0.5 at room temperature, where ρ is the thickness of the copper foil in μm.

[0057] The copper foil of this invention is extremely thin, directly reducing the weight of the battery using it and significantly improving the battery's gravimetric and volumetric energy densities. Moreover, while simply thinning the copper foil typically leads to a sharp decrease in its mechanical strength, the copper foil of this invention possesses extremely high mechanical strength, providing sufficient structural stability to the ultra-thin foil, allowing it to maintain its complete structural function even under repeated impacts during the charging and discharging of silicon-based materials. Simultaneously, thanks to its robust structural stability, it not only better supports the silicon-based material, reducing interfacial delamination caused by deformation or yielding of the current collector, but the stable platform also allows the adhesive to more effectively exert its viscoelastic effect, buffering stress and maintaining adhesion, jointly inhibiting the shedding of active materials, thereby maintaining the interfacial bonding force between the active material coating and the copper foil.

[0058] The copper foil of this invention has a gradient grain structure. On the smooth side, the copper foil grains are fine and uniform. The fine and uniform grains on the smooth side follow the Hall-Petch relationship, that is, the finer the grains, the more grain boundaries there are, which can effectively hinder dislocation movement, significantly improve the strength and hardness of the material, and the copper foil surface is smooth and flat. On the rough side, the copper foil grains are relatively coarse. The fine and uniform particles grow through deposition to form the rough surface, while the relatively coarse grains help to balance the overall performance of the material.

[0059] [Methods for preparing copper foil]

[0060] The present invention also provides a method for preparing copper foil according to the present invention, comprising the following steps:

[0061] Step 1) Prepare the electrolyte, which comprises the following components: copper ions 85-125 g / L, sulfuric acid 80-110 g / L, chloride ions 20-60 ppm, and agents A, B, and C.

[0062] Wherein, agent A is an organic divalent sulfur compound, agent B comprises polyether compounds and nitrogen-containing heterocyclic compounds, and agent C is a nitrogen-containing compound.

[0063] The total concentration of agents A, B, and C is 105-260 ppm, the concentration of agent C is 15 ppm-60 ppm, and the concentrations of agents A, B, and C satisfy the relationship: A / (B+C)=1.8-3.2;

[0064] Step 2) The electrolyte is used to prepare the copper foil by electrochemical deposition.

[0065] Agent A mentioned above is a brightener added during the electrolytic copper foil process. The brightener increases deposition resistance, inhibits deposition rate, and prolongs crystal nucleus growth time by forming an adsorption film.

[0066] Agent B mentioned above is a leveling agent added during the electrolytic copper foil process. The leveling agent strongly adsorbs onto the cathode surface, occupies active sites, inhibits the reduction of copper ions, and competes with the brightener for adsorption sites, thus jointly improving cathode polarization.

[0067] The positioning agent and brightener promote the formation of new crystal nuclei, and the two work together to achieve high-density nanocrystals, significantly improving surface gloss.

[0068] Agent C mentioned above is a leveling agent added during the electrolytic copper foil process. It preferentially adsorbs in areas with strong electric fields, such as high points / corners, forming a local diffusion barrier that forces copper ions to deposit in the depressions. At the same time, the leveling agent provides basic inhibition, and the leveling agent, combined with micro-control, achieves dual optimization from macroscopic thickness uniformity to microscopic smoothness.

[0069] Additionally, Cl reacts with brighteners, such as SPS, to form Cu. + -Cl - - Brightener (SPS) complexes enhance its adsorption stability at the cathode and can adjust the brightener efficiency. If Cl - When the content is too low, the brightening agent is insufficient; if Cl - When the content is too high, excessive adsorption leads to brittleness.

[0070] According to the preparation method of the present invention, one or more of the following (1)-(3) are satisfied:

[0071] (1) The A agent is selected from one or more of sodium dithiopropane sulfonate (SPS), sodium 3-mercapto-1-propane sulfonate, sodium thiopropane sulfonate (HP), and dimercaptosuccinic acid (DMSA), and the concentration of the A agent is 80ppm-150ppm;

[0072] (2) The agent B comprises a polyether compound and a nitrogen-containing heterocyclic compound. The polyether compound is selected from one or more of polyethylene glycol (PEG) with a molecular weight of 600-10000, polypropylene glycol (PPG) with a molecular weight of 400-2000, and polyethylene glycol-polypropylene glycol block copolymer. The nitrogen-containing heterocyclic compound is selected from one or two of polyvinylpyrrolidone (PVP) and polyvinylimidazole (PVI). The concentration of the agent B is 10-50 ppm.

[0073] (3) The agent C is selected from one or more of gelatin, collagen, polyethyleneimine (PEI) with a molecular weight of 600-100000, tetrahydrothiazothione, and chitosan derivatives.

[0074] Applications of copper foil

[0075] The present invention also provides a current collector comprising the copper foil described herein. The current collector of the present invention, by employing the copper foil of the present invention, can achieve an extremely thin thickness and extremely high tensile strength. During the cell manufacturing process, it is less prone to deformation, wrinkling, or breakage, thus improving production efficiency. Simultaneously, it can effectively resist the enormous tensile and compressive stresses generated by silicon expansion, avoiding electrode failure and the risk of internal short circuits in the battery due to copper foil tearing.

[0076] The present invention also provides an electrode sheet comprising the current collector described herein. The electrode sheet having the current collector described herein, using the copper foil described herein as a substrate, exhibits higher adhesion to silicon-based materials or other negative electrode active materials with higher coefficients of shrinkage and expansion. This helps maintain the integrity of the electrode structure, helps maintain the conductive network between negative electrode active materials and between the active materials and the current collector, reduces contact resistance, and improves battery energy density and cycle life.

[0077] This invention also provides a lithium secondary battery, comprising the electrode sheet described herein. The lithium secondary battery of this invention...

[0078] The present invention also provides an energy storage device, including the lithium secondary battery described in the present invention.

[0079] Example

[0080] Example 1

[0081] Preparation of electrolyte

[0082] Dissolve 99.9% pure copper rods and wires in concentrated sulfuric acid, inject air, and heat to 85°C to dissolve. After three-stage filtration, mix thoroughly with an aqueous solution of hydrochloric acid, agent A, agent B, and agent C.

[0083] The principle components and formulation of the electrolyte are shown in Table 1. Agent A is composed of sodium polydithiopropane sulfonate (SPS) and sodium thiopropane sulfonate (HP) in a mass ratio of 1:1.5; Agent B is composed of polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) in a mass ratio of 1:1; Agent C is composed of gelatin and polyethyleneimine (PEI) in a mass ratio of 2:1, wherein the molecular weights of PEG, PPG, and PEI are 8000, 1000, and 8000, respectively, and A / (B+C) = 2.2.

[0084] Preparation of copper foil

[0085] The copper foil is prepared by electrolytic deposition, using a cathode roller, electrolyte, and anode plate as components and media, with an externally applied current forming an electrolytic deposition circuit. The cathode roller is made of titanium, and the anode plate is a tantalum-iridium coated titanium plate; the electrolysis temperature is 52℃; and the current density is 65 A / dm³. 2 .

[0086] The deposited copper foil is rotated by the cathode roller and peeled off from the surface. After anti-oxidation treatment, a master roll with a copper foil thickness of 5μm is obtained. The master roll is then put into an oven for annealing treatment. When the warpage is measured to be <10mm, the copper foil is obtained and is denoted as copper foil-I.

[0087] Example 2

[0088] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is referred to as Copper Foil-II.

[0089] Example 3

[0090] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is designated as Copper Foil-III.

[0091] Example 4

[0092] Agent B is composed of PPG and PVP in a mass ratio of 2:1. The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is designated as Copper Foil-IV.

[0093] Example 5

[0094] Agent B is composed of PPG and PVP in a mass ratio of 2:1, and Agent C is composed of only PEI. The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and denoted as Copper Foil-V.

[0095] Example 6

[0096] Agent B consists of PPG and PVP in a mass ratio of 2:1, and Agent C consists of only PEI. The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is denoted as Copper Foil-VI.

[0097] Example 7

[0098] Agent B consists of PPG and PVP in a mass ratio of 2:1, and Agent C consists of only PEI. The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is designated as Copper Foil-VII.

[0099] Example 8

[0100] Agent B is composed of PEG and PVP in a mass ratio of 1:1, and Agent C is composed of only PEI. The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is denoted as Copper Foil-VIII.

[0101] Example 9

[0102] Agent A consists of SPS and DMSA in a mass ratio of 1:1.5, Agent B consists of PEG and PVP in a mass ratio of 1:1, and Agent C consists of only PEI. The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is denoted as Copper Foil-IX.

[0103] Example 10

[0104] Agent A consists of DMSA and HP in a mass ratio of 1:1, Agent B consists of PEG and PVP in a mass ratio of 1:1, and Agent C consists of only PEI. The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is denoted as Copper Foil-X.

[0105] Comparative Example 1

[0106] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and denoted as Copper Foil-Pair I.

[0107] Comparative Example 2

[0108] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and denoted as Copper Foil-II.

[0109] Comparative Example 3

[0110] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and is referred to as Copper Foil-Pair III.

[0111] Comparative Example 4

[0112] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and denoted as Copper Foil-IV.

[0113] Comparative Example 5

[0114] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and denoted as Copper Foil-to-V.

[0115] Comparative Example 6

[0116] The raw material components and formulation of the electrolyte are shown in Table 1. Other aspects are the same as in Example 1. Copper foil was prepared and denoted as Copper Foil-VI.

[0117] Table 1

[0118]

[0119] Tensile strength test

[0120] According to test method GB / T29847-2013, the tensile strength and elongation of copper foil were tested using a HY-0230 universal testing machine manufactured by Shanghai Hengyi Precision Instruments Co., Ltd., at a strain rate of 0.8 mm / s and room temperature (approximately 25℃). The tensile test specimens were strip specimens, 100 mm in total length and 15 mm in width. The samples were measured three times, and the average value was taken as the final tensile strength and elongation of the samples. The results are shown in Table 2.

[0121] Backscatter diffraction (EBSD) test

[0122] The microstructure of the copper foil-I obtained in Example 1 was observed using a C-Swift EBSD detector manufactured by Oxford Instruments, UK. To facilitate observation of the grain boundary profiles, the cross-section was pre-polished using an ion mill for 20 minutes. The results are shown below. Figure 1 .

[0123] The backscattered diffraction (EBSD) software used for testing was Aztec. The EBSD test results show that the copper foil grains grow from fine, uniform particles on the smooth surface to a rough surface through deposition, thanks to its unique gradient grain structure. The fine, uniform grains on the smooth surface follow the Hall-Petch relationship, meaning that the finer the grains, the more grain boundaries there are, effectively hindering dislocation movement and significantly improving the material's strength and hardness. Furthermore, the smooth, flat surface of the copper foil, along with the coarser grains on the rough surface, helps to balance the overall performance of the material.

[0124] The microstructure of the copper foils obtained in other embodiments and comparative examples was tested using the same method, and the values ​​of δ, m, n, and δ were obtained using the image processing software Aztec Crystal. The values ​​of ρ are shown in Table 2.

[0125] Application Examples 1-10 and Comparative Examples 1-6

[0126] Using copper foil from Examples 1-10 and Comparative Examples 1-6 as the negative electrode carrier, 92 parts by weight of commercially available silicon-carbon negative electrode material with a silicon content of 10%, 3 parts by weight of conductive carbon black, 3 parts by weight of SBR, and 2 parts by weight of carboxymethyl cellulose were mixed in high-purity water to prepare a negative electrode active material slurry with a viscosity of 3200-6800 mPa·s. The slurry was then coated on both sides of the carrier. After drying and rolling, the negative electrode sheet was obtained. It was then wound into a core with a lithium manganese iron phosphate positive electrode sheet and a separator, and assembled into a battery cell. After baking, liquid injection, standing, formation, and capacity testing, 20 PCS of soft-pack battery cells with a capacity of 15Ah were obtained. The cells were charged at 4.2V and discharged at 3.2V, and cyclically charged and discharged at a charge / discharge rate of 1.5 / 1C at room temperature (25℃). The number of charge / discharge cycles when the battery capacity decayed to 80% of the initial capacity was measured. The results are shown in Table 2. The cells were then fully charged and disassembled to observe the condition of the electrode sheet. The results are also shown in Table 2.

[0127] Table 2

[0128]

Claims

1. A copper foil, characterized in that, The tensile strength, thickness, and grain parameters of the copper foil satisfy the following relationship: Wherein, UHT represents tensile strength, in MPa; δ represents the number of twin grains within a rectangular area of ​​5.5μm × 26μm in the copper foil cross-section; m is the maximum value of the fitted ellipse diameter of the grains within the rectangular area, in μm; n is the minimum diameter of the fitted ellipse of the grains within the rectangular area, in μm; The average value of the fitted ellipse diameter of the grains within the rectangular area, in μm; ρ represents the thickness of the copper foil, in μm.

2. The copper foil according to claim 1, characterized in that, In the copper foil, the ratio of twinned grain regions to twinned grains is 1.0-3.

0.

3. The copper foil according to claim 1 or 2, characterized in that, The thickness of the copper foil is ≤5μm.

4. The copper foil according to claim 1 or 2, characterized in that, The copper foil has a tensile strength ≥700MPa and an elongation at break ≥ρ-0.5 at room temperature, where ρ is the thickness of the copper foil in μm.

5. A method for preparing copper foil according to any one of claims 1-4, characterized in that, Includes the following steps: Step 1) Prepare the electrolyte, which comprises the following components: copper ions 85-125 g / L, sulfuric acid 80-110 g / L, chloride ions 20-60 ppm, and agents A, B, and C. Wherein, agent A is an organic divalent sulfur compound, agent B comprises polyether compounds and nitrogen-containing heterocyclic compounds, and agent C is a nitrogen-containing compound. The total concentration of agents A, B, and C is 105-260 ppm, the concentration of agent C is 15 ppm-60 ppm, and the concentrations of agents A, B, and C satisfy the relationship: A / (B+C)=1.8-3.2; Step 2) The electrolyte is used to prepare the copper foil by electrochemical deposition.

6. The preparation method according to claim 5, characterized in that, It meets one or more of the following conditions (1)-(3): (1) The A agent is selected from one or more of sodium dithiopropane sulfonate (SPS), sodium 3-mercapto-1-propane sulfonate, sodium thiopropane sulfonate (HP), and dimercaptosuccinic acid (DMSA), and the concentration of the A agent is 80ppm-150ppm; (2) The agent B comprises a polyether compound and a nitrogen-containing heterocyclic compound. The polyether compound is selected from one or more of polyethylene glycol (PEG) with a molecular weight of 600-10000, polypropylene glycol (PPG) with a molecular weight of 400-2000, and polyethylene glycol-polypropylene glycol block copolymer. The nitrogen-containing heterocyclic compound is selected from one or two of polyvinylpyrrolidone (PVP) and polyvinylimidazole (PVI). The concentration of the agent B is 10-50 ppm. (3) The agent C is selected from one or more of gelatin, collagen, polyethyleneimine (PEI) with a molecular weight of 600-100000, tetrahydrothiazothione, and chitosan derivatives.

7. A current collector comprising the copper foil according to any one of claims 1-4.

8. An electrode comprising the current collector as described in claim 7.

9. A lithium secondary battery comprising the electrode as described in claim 8.

10. An energy storage device comprising the lithium secondary battery of claim 9.

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