Additive for electrolytic copper foil, electrolyte, low-warpage ultrahigh-strength copper foil, preparation method of low-warpage ultrahigh-strength copper foil, current collector and pole piece

Abstract

The invention relates to the technical field of electrolytic copper foils, in particular to an additive for an electrolytic copper foil, an electrolyte, a low-warpage ultrahigh-strength copper foil, a preparation method of the low-warpage ultrahigh-strength copper foil, a current collector and a pole piece. The additive is composed of a brightener, a displacement agent, a leveling agent and a chelating agent according to the mass concentration ratio of (20-60): (10-40): (3-15): (30-120). After the copper foil is aged in a drying oven at 85 DEG C for 30-100 H, the warping of the copper foil is smaller than or equal to 10 mm. The thickness of the copper foil is 8 [mu] m, and the tensile strength of the copper foil is 500-700 MPa; the ductility of the copper foil is larger than or equal to 6%. According to the additive for the electrolytic copper foil, provided by the invention, the chelating agent in the additive can be combined with a brightening agent, a walking agent and a leveling agent for use, and is mainly used for promoting nucleation of copper ions in an electrochemical deposition process, so that the prepared copper foil is more uniform, flat and compact in grain structure, the internal stress difference value of a G surface and an M surface of the copper foil can be effectively reduced, and warping is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrolytic copper foil, in particular to an additive for electrolytic copper foil, an electrolyte, a low-warp ultra-high-strength copper foil, a preparation method thereof, a current collector and a pole piece. BACKGROUND

[0002] A lithium ion battery (LIB) is a kind of secondary battery that realizes charging and discharging through reversible migration of lithium ions between the positive and negative electrodes. Due to its high energy density, long cycle life, low self-discharge rate and other advantages, it has become one of the most influential energy storage technologies.

[0003] As one of the important components of a lithium ion battery, a current collector not only can carry active materials, but also can collect and output the current generated by the active materials, reduce the internal resistance of the lithium ion battery, and improve the coulomb efficiency, cycle stability and rate performance of the battery. Therefore, the lithium ion battery current collector needs to meet the following elements: ① high electrical conductivity; ② good electrochemical stability; ③ high mechanical strength and ductility; ④ good compatibility and binding force with electrode active materials; ⑤ cheap and easy to obtain; ⑥ light weight, etc. Copper foil is often used as the current collector of graphite and silicon negative active materials due to its excellent electrical conductivity and many advantages such as abundant resources, cheapness, easy availability and good ductility.

[0004] In order to improve the energy density of lithium ion batteries, the pursuit of current collector copper foil has been developing towards lightness and high tensile strength. However, with the use of high-energy-density silicon-carbon negative electrodes, changes in battery structure design, and the introduction of more stringent national safety standards, relatively thin copper foil (<6 μm) still occupies an important position in lithium battery copper foil current collectors. First, the mechanical strength of ultra-thin copper foil is higher, the processing difficulty is reduced, the production yield and efficiency are improved, and the comprehensive cost is more advantageous. Second, the innovation of new battery structures such as CTP (Cell to Pack) and blade battery requires higher mechanical support for current collector copper foil, and ultra-thin copper foil can better meet the structural strength requirements. Finally, thicker copper foil has lower resistance, can withstand larger current, reduces the heating problem during fast charging, improves the high-rate performance of the battery, and has better mechanical stability, which can prolong the service life of the battery and reduce the risk of short circuit, meeting the demand for higher safety standards.

[0005] As the core material of lithium ion battery negative electrode current collector, the surface flatness and mechanical properties of electrolytic copper foil directly affect the capacity density, cycle life and safety of the battery. In the conventional copper sulfate electrolysis system, the warping problem of copper foil is one of the key factors restricting its quality. In the process of electrolytic deposition of copper foil, copper ions are reduced to metal copper on the surface of the cathode roller with a certain roughness and form grains, while the additives in the electrolyte control the copper deposition rate and uniformity through adsorption. At high current density, copper ions are quickly deposited and grow vertically, forming columnar crystal structure. In the process of stripping, cleaning, annealing and slitting and winding, stress concentration occurs, and finally the copper foil shows a warped state. The warping of copper foil affects the whole life cycle of battery production (coating, slitting) and use (cycle, safety), directly leading to the decline of electrode quality, energy density, cycle life and the risk of thermal runaway. Therefore, controlling the warping of copper foil is a key technical challenge to improve the performance and reliability of lithium ion batteries. SUMMARY

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present application is to provide an additive for electrolytic copper foil, an electrolyte, a low-warping ultra-high-strength copper foil and a preparation method thereof, a current collector and an electrode sheet, to solve the problem of easy warping during the preparation of copper foil in the prior art.

[0007] To achieve the above-mentioned purposes and other related purposes, the present application is obtained by the following technical solutions.

[0008] The first aspect of the present application provides a low-warping high-strength copper foil, which has a warping of less than or equal to 10 mm after being aged in an 85℃ oven for 30-100H.

[0009] The second aspect of the present application provides a preparation method of a low-warping high-strength copper foil, which is prepared by an electrolytic method. The electrolyte used in the electrolytic method comprises the following raw materials with the following mass concentrations: Cu 2+ 85-95g / L, H2SO4110-115g / L, Cl - 25-35ppm, brightener 20-60ppm, walking agent 10-40ppm, leveling agent 3-15ppm, chelating agent 30-120ppm, the chelating agent being DTPA-benzothiazole conjugate.

[0010] The third aspect of the present application provides an additive for electrolytic copper foil, which is composed of a brightener, a walking agent, a leveling agent and a chelating agent in a mass concentration ratio of 20-60:10-40:3-15:30-120, the chelating agent being DTPA-benzothiazole conjugate.

[0011] The fourth aspect of the present application provides an electrolyte for electrolytic copper foil comprising the additive for electrolytic copper foil as described above. Preferably, the electrolyte comprises raw materials in the following mass concentrations: Cu 2+ 85-95 g / L, H2SO4110-115 g / L, Cl - 25-35 ppm, brightener 20-60 ppm, leveler 10-40 ppm, leveling agent 3-15 ppm, chelating agent 30-120 ppm, the chelating agent being DTPA-benzothiazole conjugate.

[0012] The fifth aspect of the present application provides a current collector comprising the copper foil as described above.

[0013] The sixth aspect of the present application provides a pole piece comprising the current collector as described above.

[0014] The seventh aspect of the present application provides a secondary battery comprising the pole piece as described above.

[0015] As described above, the additive for electrolytic copper foil, the electrolyte, the low-warp ultra-high-strength copper foil and the preparation method thereof, the current collector, and the pole piece of the present application have the following beneficial effects:

[0016] (1) The present application provides an additive for electrolytic copper foil. The chelating agent in the additive can be used in combination with the brightener and the leveler. It mainly promotes the nucleation of copper ions in the electrochemical deposition process. When used in combination with the leveling agent, the copper foil has a more uniform, flat and dense grain structure, which can effectively reduce the internal stress difference between the G surface and the M surface of the copper foil, and reduce the warping.

[0017] (2) The copper foil prepared by the present application has low warping and high strength. The low warping property ensures that the copper foil remains flat when coating the negative electrode paste, avoids uneven coating thickness, improves electrode consistency, reduces local current density differences, and optimizes battery charge and discharge efficiency. The low-warp copper foil reduces the deformation risk of the pole piece in the winding or lamination process, reduces the probability of poor contact or puncture between the electrode and the separator, and improves the safety of the battery. The ultra-high tensile strength of the copper foil makes it more resistant to stretching and mechanical stress during battery manufacturing (such as coating, rolling, and slitting) and use, reducing the risk of processing breakage and improving production yield. At the same time, it can effectively resist the deformation or rupture of the current collector caused by expansion, thereby prolonging the cycle life of the battery.

[0018] (3) The ultra-high tensile strength of the copper foil of the present application allows the copper foil to have sufficient mechanical support even when it is thinner, reduces the resistance of the current collector, thereby reducing the internal resistance of the battery and improving the fast-charging performance and power output. At the same time, for high-expansion-coefficient silicon-based negative electrodes or metal lithium negative electrodes, the ultra-high-strength copper foil can better withstand the stress of repeated expansion / contraction, delay the fatigue failure of the current collector, and facilitate the development of the next generation of high-capacity batteries.

[0019] (4) The high mechanical stability of the copper foil is suitable for high processing rate (coating, rolling, slitting, etc.) and ensures good yield, improving the overall efficiency of the equipment; at the same time, the high cycle stability of the copper foil indirectly reduces the replacement frequency of the battery throughout its life cycle, improves resource utilization efficiency, and realizes cost reduction and efficiency improvement. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 EBSD diagram of the low-warp high-strength copper foil prepared in Example 2 of the present application.

[0021] Figure 2 Warp photo of the low-warp high-strength copper foil prepared in Example 5 of the present application.

[0022] Figure 3 Warp photo of the qualified high-strength copper foil prepared in Example 2 of the present application.

[0023] Figure 4 Warp photo of the high-warp high-strength copper foil prepared in Comparative Example 5 of the present application. DETAILED DESCRIPTION

[0024] In order to make the invention purpose, technical scheme and beneficial technical effects of the present application clearer, the present application will be further described in detail below in combination with examples, and those skilled in the art can easily understand other advantages and effects of the present application from the content disclosed in the present specification.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein only for the purpose of describing specific embodiments and is not intended to limit the present application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0026] In the case of using "comprising", "having", and "including" described herein, it is intended to cover non-exclusive inclusion, unless an explicit limiting term such as "only", "consisting of", etc. is used, otherwise another component can be added.

[0027] The words "preferably," "more preferably," "most preferably," and the like, in the present invention, mean that in certain situations, embodiments of the invention can provide certain benefits. However, other embodiments can also be preferred under the same or other circumstances. Furthermore, the recitation of one or more preferred embodiments does not imply that other embodiments are not useful, and is not intended to exclude those other embodiments from the scope of the present invention. That is, in the present invention, "preferably," "more preferably," "most preferably," and the like, merely mean that a better result is obtained, but do not constitute a limitation of the scope of the present invention.

[0028] In the present invention, "further," "even further," "in particular," and the like, are used to describe purposes and indicate differences in content, but should not be understood as limiting the scope of the present invention.

[0029] In the present invention, "at least one" means one or more, such as one, two, and more than two. "Multiple" or "several" means at least two, such as two, three, and the like. "Multiple layers" means at least two layers, such as two, three, and the like, unless otherwise explicitly specified. In the description of the present invention, "several" means at least one, such as one, two, and the like, unless otherwise explicitly specified.

[0030] When a numerical range is disclosed herein, the range is to be construed as continuous, and includes the minimum and maximum values of the range, as well as every value between the minimum and maximum values. Further, when a range is disclosed, the range includes every integer within the range, unless otherwise indicated. Moreover, when a plurality of ranges is provided, the ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood to be inclusive of any and all sub-ranges subsumed therein.

[0031] If not specifically stated, all steps of the present invention can be performed in sequence, or randomly. For example, the method comprises steps (a) and (b), indicating that the method can comprise steps (a) and (b) in sequence, or steps (b) and (a) in sequence. For example, the method is mentioned to further comprise step (c), indicating that step (c) can be added to the method in any sequence, for example, the method can comprise steps (a), (b), and (c), or steps (a), (c), and (b), or steps (c), (a), and (b), and the like.

[0032] Unless otherwise mentioned, the singular form of a term can include the plural form and is not to be construed as limited to a quantity of one

[0033] In the present invention, "above" or "below" includes the number. For example, 1 below includes 1.

[0034] In the present invention, room temperature refers to 0-40℃, including but not limited to 10-40℃, or further 20-30℃.

[0035] In the present invention, the G face and the M face of the copper foil are specifically: the copper foil has two faces, the G face refers to the smooth face, that is, the face that contacts the cathode roller when the copper foil is deposited on the cathode roller, and the M face refers to the rough face, that is, the face that does not contact the cathode roller, that is, the other face opposite to the smooth face.

[0036] When the negative current collector copper foil is co-wound or laminated with the positive electrode sheet, the separator and the like to form an electrode assembly, excessive warpage (> 10 mm) will cause interlayer alignment deviation, increase the risk of short circuit; at the same time, it will increase the difficulty of equipment debugging during the process, leading to production interruption or rising of waste rate, reducing production efficiency; or when the battery is subjected to extrusion or vibration, the copper foil will pierce the separator, causing internal short circuit, even thermal runaway. Low warpage (≤ 10 mm) copper foil not only avoids the collapse of the electrode structure caused by local stress concentration, prolongs the battery life; but also enables tighter electrode stacking, and improves the volume energy density of the battery.

[0037] The secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, while allowing ions to pass through.

[0038] The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, and the positive active material layer includes a positive active material. The positive current collector can be a metal foil; for example, an aluminum foil. The positive active material can be a positive active material known in the art for use in batteries. Such as lithium iron phosphate, lithium manganese phosphate, etc.

[0039] The positive active material layer can also optionally include a binder. As a non-limiting example, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE).

[0040] The positive active material layer can also optionally include a conductive agent. As a non-limiting example, the conductive agent can include one or more of super conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0041] The method for preparing the positive electrode sheet includes the steps of dispersing the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector; and drying, cold-pressing, and the like to obtain the positive electrode sheet. The type of the solvent can be a solvent commonly known in the art for use in a battery, such as N-methylpyrrolidone (NMP). The positive electrode slurry can be coated on a single surface of the positive electrode current collector or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5,000 to 25,000 mPa·s. When the positive electrode slurry is coated, the coating unit area density can be 15 to 35 mg / cm 2 , in terms of dry weight (excluding the solvent). The positive electrode sheet can have a compacted density of 3.0 to 3.6 g / cm 3 , and can optionally have a compacted density of 3.3 to 3.5 g / cm 3 .

[0042] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material. The negative electrode current collector is the electrolytic copper foil prepared according to the present application. The negative electrode active material can be a negative electrode active material commonly known in the art for use in a battery. As non-limiting examples, the negative electrode active material can include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, lithium titanate, and the like. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative electrode active material for a battery can also be used.

[0043] The negative electrode active material layer can also optionally include a binder. The binder can include one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), and carboxymethyl chitosan (CMCS).

[0044] The negative electrode active material layer can also optionally include a conductive agent. The conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0045] The method for preparing the negative electrode sheet includes the following steps: dispersing the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative electrode current collector, and after processes such as drying, cold pressing and the like, the negative electrode sheet can be obtained. The solid content of the negative electrode slurry can be 40wt%-60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s-10000mPa·s. When the negative electrode slurry is coated, the coating unit area density, in terms of dry weight (excluding the solvent), can be 75-220g / m 2 . The compaction density of the negative electrode sheet can be 1.0-1.8g / cm 3 .

[0046] The kind of electrolyte is not particularly limited in the present application, and can be selected according to the needs. For example, the electrolyte can be liquid, gel or all-solid-state.

[0047] The kind of separator film is not particularly limited in the present application, and any known porous structure separator film with good chemical stability and mechanical stability can be selected. The material of the separator film can include one or more of polyethylene, polypropylene and polyvinylidene fluoride.

[0048] In order to improve the warping problem of copper foil, Hang et al. (patent CN 118957686A) improved the uniformity of copper deposition by adjusting the type and concentration of additives in the electrolyte, optimizing the electrolyte formula, and improving the warping of copper foil. Xu et al. (patent CN 111793779A) improved the flexibility and fatigue resistance of copper foil by adopting gradient annealing process, constant speed heating and cooling, avoiding thermal shock and promoting grain boundary migration and dislocation recombination, and reducing the warping of copper foil.

[0049] Although the method of improving the warping of copper foil by optimizing the electrolyte formula has low cost and high flexibility, it still has many drawbacks. First, the synergistic effect between additives is complex. For example, the adsorption competition between chloride ions (Cl-) and polyethylene glycol (PEG) may destroy the uniformity of the deposition layer. Excessive Cl- will accelerate the cathode passivation, while excessive PEG concentration will inhibit the migration of copper ions, leading to fluctuation of deposition rate, and even exacerbate the uneven thickness. Second, although thiourea brightener can refine the grain size, its decomposition products (such as sulfides) are easy to remain in the copper foil, increasing the impurity content, reducing the conductivity and corrosion resistance, and affecting the battery performance. In addition, the dynamic consumption of additives needs to be monitored in real time. If it is not replenished in time, the imbalance of electrolyte components will lead to poor batch stability and increase the difficulty of quality control. In the long run, formula adjustment may cover up process or equipment defects. If too much reliance is placed on additives, it will hinder the in-depth exploration of the deposition mechanism and restrict the technology iteration.

[0050] Gradient annealing needs to control temperature in stages and prolong the processing time, compared with the conventional annealing, the energy consumption increases by 20-30%, and it depends on high-precision temperature control equipment, the equipment investment and maintenance cost increases significantly; if the cooling rate is not uniform in the cooling stage, the difference in interlayer thermal shrinkage may induce new thermal stress, which is easy to cause wavy edges; some gradient annealing needs to be completed in an inert atmosphere (such as nitrogen), if the atmosphere purity is insufficient or the sealing is not strict, the copper foil surface is easy to be oxidized to generate cuprous oxide (Cu2O), or adsorb impurity particles, which reduces the conductivity and interface bonding force.

[0051] The additive for electrolytic copper foil provided by the application can be combined with brightener, walking agent and leveling agent to promote the nucleation of copper ions in the electrochemical deposition process, so that the copper foil grain structure is more uniform, flat and dense, and the internal stress difference of the copper foil G surface and M surface can be effectively reduced, and the warping can be reduced.

[0052] The first aspect of the application provides a low-warping high-strength copper foil, the warping of the copper foil is ≤10 mm after aging in an 85℃ oven for 30-100 h. Specifically, the warping can be 6-8 mm, 8-10 mm.

[0053] The aging time here refers to the time required for the copper foil to achieve a warping of ≤10 mm. Specifically, for an 8μm high-strength copper foil (500-600MPa), the initial baking temperature and time are uniform, such as 85℃ baking for 60 h. When the time reaches 60 h, the warping is measured and is 12, which does not meet the requirement of <10 mm. At this time, the baking time is further increased by 20 h. If the requirement is still not met, the baking time can be further increased, provided that no color difference or crease appears on the foil surface after baking. The baking time here refers to the total baking time, that is, the time required for the warping to meet the requirement after baking, such as 90 h, which can be 60 h+20 h+10 h, the total time of three baking times.

[0054] The copper foil of the application has the property of low warping. On the one hand, the low warping property ensures that the copper foil remains flat when the negative electrode paste is coated, avoids uneven coating thickness, improves electrode consistency, reduces local current density difference, and optimizes battery charging and discharging efficiency. On the other hand, low warping reduces the risk of deformation of the electrode sheet in the winding or lamination process, reduces the probability of poor contact or puncture between the electrode and the separator, and improves the safety of the battery.

[0055] In some embodiments of the application, the thickness of the copper foil is 8μm, the tensile strength of the copper foil is 500-700MPa, and the elongation of the copper foil is ≥6%.

[0056] In some embodiments of the application, the cross section of the low-warping ultra-high-strength copper foil has similar grain size and uniform distribution, the grain fitting ellipse major and minor axis ratio is Γ, and the range is 1-10, and the Γ satisfies:

[0057]

[0058] Wherein, θ represents sample inclination angle; ρ represents correction coefficient, the value range is 0.5-4.0; a, b respectively represent long radius and short radius (μm) of fitting ellipse.

[0059] The present application introduces the ratio of long and short axes of grain fitting ellipse to limit the grain size and distribution of copper foil, and the long and short axes of fitting ellipse can represent the anisotropy of grain, wherein the long axis reflects the preferred orientation (such as (110), (100) texture, etc.) of grain in a particular direction, and the elastic modulus is generally higher, and the short axis mainly represents the compression state in the vertical direction, and plastic deformation is easy to occur, when the ratio Γ of long and short axes is larger (>10), the shape anisotropy of grain is stronger, resulting in stress concentration, especially in the edge area of copper foil, high warping occurs.

[0060] When the low-warping ultra-high-strength copper foil satisfies the formula, the grain size of the copper foil light matte surface is relatively uniform, there are no obvious large or small particles, the stress difference of the light matte surface is small, and the warping is low.

[0061] Wherein, the selection of ρ value is related to the short radius b of fitting ellipse, when b is too small, the difference between long and short axes is obvious, and the correction coefficient is small; when b is larger, the difference between long and short axes is not obvious, and the correction coefficient is larger; theoretically, 0.25 μm is a unit, and the correction coefficient of each unit is 0.5, but actually, less than 0.1 μm is calculated as one correction coefficient, 0.1-0.5 μm is calculated as two correction coefficients, 0.5-1 μm is calculated as four correction coefficients, 1-1.5 μm is calculated as six correction coefficients, and >1.5 μm is calculated as eight correction coefficients; specifically: when b<0.1, the coefficient is 0.5;

[0062] When b is 0.1-0.5, the coefficient is 1;

[0063] When b is 0.5-1, the coefficient is 2;

[0064] When b is 1-1.5, the coefficient is 3;

[0065] When b>1.5, the coefficient is 4.

[0066] In some embodiments of the present application, the Γ can be 4-5, 5-6, 6-7, 7-8, 8-9.5.

[0067] The second aspect of the present application provides a preparation method of low-warping high-strength copper foil, and the copper foil is prepared by an electrolysis method, and the electrolyte used in the electrolysis method comprises raw materials with the following mass concentrations: Cu 2+ 85-95 g / L, H2SO4110-115 g / L, Cl -25-35ppm, brightener 20-60ppm, walking agent 10-40ppm, leveling agent 3-15ppm, chelating agent 30-120ppm, the chelating agent is DTPA-benzothiazole conjugate.

[0068] In some embodiments of the present application, the temperature of the electrolyte is 20-50℃. Specifically, the temperature can be 20-40℃, 40-50℃. Typically but not limitedly, for example, 20℃, 40℃, 50℃.

[0069] In some embodiments of the present application, the current density of the electrolysis is 65-85A / dm 2 ; specifically, the current density can be 65-75A / dm 2 , 75-85A / dm 2 . Typically but not limitedly, for example, 65A / dm 2 , 75A / dm 2 , 85A / dm 2 .

[0070] In some embodiments of the present application, the cathode material used in the electrolysis can be selected from conventional anode electrode materials in the art; specifically, it can be a cathode roller with a titanium ring as the roller surface.

[0071] In some embodiments of the present application, the anode material used in the electrolysis can be selected from conventional anode electrode materials in the art; specifically, it can be a tantalum-coated titanium plate, a tantalum-coated iridium titanium plate, or a ruthenium-iridium-titanium ternary coated titanium plate.

[0072] The third aspect of the present application provides an additive for electrolytic copper foil, which is composed of brightener, walking agent, leveling agent, and chelating agent in a mass concentration ratio of 20-60:10-40:3-15:30-120, and the chelating agent is DTPA-benzothiazole conjugate.

[0073] The present application provides an additive for electrolytic copper foil, which adds a chelating agent. The purity of the electrolyte is extremely high in the production of electrolytic copper foil. A small amount of metal impurity ions (such as Fe 3+ , Zn 2+ , Ni 2The impurities (such as Fe2+, Cu2+, Zn2+, Ni2+, Co2+, Mn2+, Cr3+, Cd2+, Pb2+, Hg2+, Ag+, Cl-, SO42-, NO3-, F-, C2O42-, C6H5O7-2, etc.) in the electrolyte will seriously affect the deposition quality of copper foil (such as roughness, burning, holes, and mechanical property reduction). The strong chelating ability of DTPA-benzothiazole conjugate may improve the copper foil quality in two ways. On the one hand, the effective complexation of these impurity ions by the leveling agent may purify the electrolyte and improve the copper foil quality by co-depositing with copper at the cathode or interfering with the copper deposition process. On the other hand, the leveling agent may play a similar role in refining the grain size, improving the surface flatness, and inhibiting the growth of specific crystal faces by adsorbing on the copper electrode surface to affect the reduction and crystallization process of copper ions. At the same time, the leveling agent may have a synergistic effect with the brightener to improve the copper foil properties.

[0074] The four components of chelating agent, brightener, leveling agent, and smoothing agent are added to the additive to synergistically regulate the deposition and growth of copper ions in the electrochemical deposition process. The brightener adsorbs on the high-activity sites of the cathode surface to increase the cathode polarization and promote grain refinement. The leveling agent forms a dynamic barrier on the cathode surface to reduce the surface tension of the electrolyte, enhance the wettability of the cathode, and balance the copper deposition rate. The smoothing agent preferentially adsorbs on the micro convex areas to inhibit copper deposition in that area through steric hindrance or charge repulsion and continuously regulates the micro morphology of the deposition interface through dynamic adsorption-desorption balance.

[0075] In some embodiments of the present application, the DTPA-benzothiazole conjugate can be one or more of DTPA-benzothiazole, DTPA-2-amino benzothiazole, and DTPA-2-mercapto benzothiazole. Preferably, the DTPA-benzothiazole conjugate is DTPA-benzothiazole, and the preparation method of the DTPA-benzothiazole includes the following steps: dissolving commercially available DTPA dianhydride in anhydrous solvent under dry inert atmosphere (such as argon or nitrogen); adding a calculated amount of organic base (at least 2 equivalents to neutralize the carboxylic acid generated in the reaction and catalyze the reaction); slowly adding a solution of 2-amino benzothiazole (dissolved in a small amount of anhydrous solvent) to the DTPA dianhydride solution under ice bath cooling (0-5°C); after the addition is complete, remove the ice bath and stir the reaction mixture at room temperature; monitor the reaction progress by HPLC; finally, slowly pour the reaction mixture into a large amount of ice ether or ice ethanol; precipitate the target product DTPA-2-amino benzothiazole. The anhydrous solvent is tetrahydrofuran, and the organic base is an aliphatic amine, preferably triethylamine. The molar ratio of DTPA dianhydride, organic base, and 2-amino benzothiazole is 1:3:1. When using reverse phase HPLC (such as C18 column) to monitor the reaction, the main observation is the appearance and stability of the target product (DTPA-benzothiazole monoamide monoanhydride) peak. When the peak area no longer increases significantly (the peak area changes <2% for two consecutive samples), and the raw material peak basically disappears, it indicates that the reaction is complete.

[0076] In some embodiments of the present application, the selection of the leveling agent is not particularly limited, and a commercially available product of the leveling agent commonly used by those skilled in the art can be used. Specifically, the leveling agent is a nitrogen-containing amine organic substance, and preferably, the leveling agent is selected from one or more of collagen, gelatin, gentian violet, 2-mercaptobenzothiazole (MBT), tetrahydrothiazole thione, or isonicotinic acid. The addition of the leveling agent facilitates the filling of micro recesses, eliminates surface defects, and improves thickness uniformity. The leveling agent is usually preferentially adsorbed in high current density areas to inhibit excessive deposition.

[0077] In some embodiments of the present application, the selection of the leveling agent is not particularly limited, and a commercially available product of the leveling agent commonly used by those skilled in the art can be used. Specifically, the leveling agent is a nitrogen-containing amine organic substance, and preferably, the leveling agent is selected from one or more of collagen, gelatin, gentian violet, 2-mercaptobenzothiazole (MBT), tetrahydrothiazole thione, or isonicotinic acid. The addition of the leveling agent facilitates the filling of micro recesses, eliminates surface defects, and improves thickness uniformity. The leveling agent is usually preferentially adsorbed in high current density areas to inhibit excessive deposition.

[0078] In some embodiments of the present application, the selection of the leveling agent is not particularly limited, and a commercially available product of the leveling agent commonly used by those skilled in the art can be used. Specifically, the leveling agent is a nitrogen-containing amine organic substance, and preferably, the leveling agent is selected from one or more of collagen, gelatin, gentian violet, 2-mercaptobenzothiazole (MBT), tetrahydrothiazole thione, or isonicotinic acid. The addition of the leveling agent facilitates the filling of micro recesses, eliminates surface defects, and improves thickness uniformity. The leveling agent is usually preferentially adsorbed in high current density areas to inhibit excessive deposition.

[0079] In some embodiments of the present application, the mass concentration ratio of the brightener, the leveling agent, the chelating agent, and the dispersing agent is 20-60:10-40:3-15:30-120. Specifically, the mass concentration ratio can be 20-40:10-25:3-8:30-80, 40-60:25-40:8-15:80-120.

[0080] The fourth aspect of the present application provides an electrolyte for electrolytic copper foil, comprising the additive for electrolytic copper foil as described above. Preferably, the electrolyte comprises raw materials in the following mass concentrations: Cu 2+ 85-95 g / L, H2SO4110-115 g / L, Cl - 25-35 ppm, brightener 20-60 ppm, leveler 10-40 ppm, flattening agent 3-15 ppm, chelating agent 30-120 ppm.

[0081] In some embodiments of the present application, the electrolyte comprises raw materials in the following mass concentrations: Cu 2+ 85-95 g / L, H2SO4110-115 g / L, Cl - 25-35 ppm, brightener 20-40 ppm, leveler 10-25 ppm, flattening agent 3-8 ppm, chelating agent 30-80 ppm.

[0082] In some embodiments of the present application, the electrolyte comprises raw materials in the following mass concentrations: Cu 2+ 85-95 g / L, H2SO4110-115 g / L, Cl - 25-35 ppm, brightener 40-60 ppm, leveler 25-40 ppm, flattening agent 8-15 ppm, chelating agent 80-120 ppm.

[0083] In some embodiments of the present application, the method for preparing the electrolyte is to dissolve copper sulfate, sulfuric acid, sodium chloride, flattening agent, brightener, leveler and chelating agent in water, and fully stir to mix uniformly, so that the concentrations of the components in the electrolyte meet the above requirements.

[0084] The fifth aspect of the present application provides a current collector, comprising the copper foil as described above.

[0085] The sixth aspect of the present application provides a pole piece, comprising the current collector as described above.

[0086] The low-warpage, high-strength copper foil obtained in this application is used to prepare electrodes. High warpage of the current collector copper foil has a significant impact on the cell manufacturing process and performance. On the one hand, during the manufacturing process, high copper foil warpage can easily lead to uneven coating of active materials during the coating process, resulting in thickness fluctuations, edge warping, or coating peeling. In the winding or stacking process, high-warpage copper foil can cause misalignment of the positive and negative electrodes, increasing the risk of short circuits. In the rolling process, uneven stress may cause uneven electrode surface, or even microcracks, affecting conductivity and mechanical strength. On the other hand, in terms of battery performance, high electrode warpage can easily lead to poor contact between copper foil and active material, increasing interface resistance. It may also disrupt the continuity of the conductive network, reducing the battery's rate performance (such as fast charging capability). During charging and discharging, electrodes with high warpage are subjected to greater mechanical stress when lithium ions are inserted / extracted, which may accelerate the shedding of active material or the breakage of current collector, leading to faster capacity decay. Furthermore, local stress concentration may also cause micro-short circuits, accelerate battery aging, and even cause thermal runaway, exacerbating safety hazards.

[0087] In some embodiments of the present invention, the equipment overall utilization rate (OEE) of the electrode during the coating preparation process is ≥85%.

[0088] Overall Equipment Effectiveness (OEE) is a core Key Performance Indicator (KPI) in manufacturing, used to measure the ratio of the actual effective output of manufacturing equipment or production lines to their theoretical maximum capacity. It reveals how far an equipment or production line is from achieving "perfect production" in terms of overall performance in terms of time, speed, and quality. This is a concept in industrial production, calculated based on production efficiency and process capability.

[0089] OEE = Time Availability × Performance Availability × Product Quality Rate

[0090] 1. Operating Time: The ratio of actual equipment operating time to planned production time. Reflects downtime losses;

[0091] 2. Performance utilization rate: The ratio of the actual output speed of equipment during operation to its design (or theoretical) speed. It reflects speed losses and losses from short downtime.

[0092] 3. Qualified Product Rate: The proportion of qualified products to the total number of products actually produced (including qualified and unqualified products). It reflects quality losses.

[0093] The device comprehensive utilization rate measures the cost of production and manufacturing, and has certain correlation with the performance of the copper foil, especially the warping of the copper foil. If the warping of the copper foil is too high (greater than 10 mm), the negative electrode slurry is difficult to be evenly attached to the back roll of the coating machine in the coating process, resulting in uneven coating (thickness deviation, missing coating, and striping), intensified edge effect, and even directly causing coating breakage and wrinkling. This is one of the primary factors affecting the coating yield; in the winding or lamination process, the warped copper foil causes the electrode sheet to fail to be accurately aligned, resulting in misalignment, uneven edges, and "S" shaped bending, which seriously affects the regularity of the internal structure of the battery cell and increases the risk of short circuit; in the winding process, the warped foil is not accurately positioned during slitting or die cutting, resulting in size deviation, increased burrs, and even damaged tools; these directly affect material loss and equipment efficiency loss, that is, directly affect the device comprehensive utilization rate.

[0094] The seventh aspect of the present application provides a secondary battery comprising the electrode sheet as described above.

[0095] The application will be further described by the following examples, but the scope of the application is not limited by the examples.

[0096] When a numerical range is given in the examples, it should be understood that, unless otherwise specified by the present application, both endpoints of each numerical range and any number between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present application have the same meaning as commonly understood by those skilled in the art. Unless otherwise specified, the specific conditions in the examples are carried out according to conventional conditions or manufacturer's recommended conditions. All reagents or instruments, unless otherwise specified, are conventional products that can be purchased on the market. In addition to the specific methods, devices, and materials used in the examples, any method, device, and material of the prior art similar or equivalent to those described in the examples of the present application can also be used to implement the present application according to the mastery of the prior art by those skilled in the art and the description of the present application.

[0097] Examples

[0098] Table 1 Raw materials and raw material component allocation ratio of electrolyte of examples 1-8 and comparative examples 1-9

[0099]

[0100]

[0101] Example 1

[0102] The embodiment provides a preparation method of a low-warp high-strength copper foil, which comprises the following steps: preparing the copper foil by an electrolysis method, taking a cathode roller, an electrolyte and an anode plate as component parts and media, and externally applying a current to form an electrolytic deposition loop. The cathode roller is made of a titanium plate, and the anode plate is made of a tantaled iridium titanium plate; the electrolysis temperature is 45 DEG C; the current density is 75 A / dm 2 ; and the preparation method of the electrolyte comprises the following steps: dissolving copper sulfate, sulfuric acid, sodium chloride, a leveling agent, a brightener, a walking agent and a chelating agent in water, and fully stirring and uniformly mixing. The raw material components and the proportion of the electrolyte are shown in Table 1. The brightener is composed of SPS and MPS at a mass ratio of 1:3; the walking agent is composed of PEI and polyethylene glycol (8000) at a mass ratio of 3:1, the leveling agent is Kenagreen, and the chelating agent is DTPA-2-aminobenzothiazole.

[0103] After the oxidation-preventing treatment, the 8-micron high-strength current collector copper foil is obtained from the surface of the cathode roller, the tensile strength of the copper foil is 542.7 MPa, the elongation rate is 12.8%, and the actual warp is 10 mm after baking at 85 DEG C for 60 hours.

[0104] The embodiment provides a pole piece, specifically, the copper foil is used as a negative pole piece carrier, 95 parts of a commercially available silicon-carbon negative electrode material, 2 parts of conductive carbon black, 2 parts of SBR and 1 part of carboxymethyl cellulose are mixed in high-purity water to prepare negative electrode active material slurry, the negative electrode active material slurry is coated, dried, rolled and cut to obtain a negative pole piece, and the comprehensive equipment efficiency OEE of the process is 86.3%. The coating surface density is 135 mg / cm 2 ; and the compaction density of the negative pole piece is 1.50 g / cm 3 .

[0105] Example 2

[0106] The embodiment provides a preparation method of a low-warp high-strength copper foil, and the raw material components and the proportion of the electrolyte are shown in Table 1. The difference between the embodiment and example 1 lies in that the raw material proportion of the electrolyte is different. The brightener is composed of SPS and MPS at a mass ratio of 1:2; the walking agent is composed of PEI and polyethylene glycol (8000) at a mass ratio of 3:2, and the leveling agent is Kenagreen.

[0107] The EBSD image of the copper foil prepared in the embodiment is shown in Figure 1 The EBSD image of the copper foil prepared in the embodiment is shown in

[0108] Example 3

[0109] The embodiment provides a preparation method of low-warp high-strength copper foil, and raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the embodiment 1 is that raw material proportions of the electrolyte are different. A brightener is composed of SPS and MPS in a mass ratio of 1:2; a leveling agent is composed of PEI and polyethylene glycol (8000 in molecular weight) in a mass ratio of 3:1, and a smoothing agent is Kenagreen.

[0110] Embodiment 4

[0111] The embodiment provides a preparation method of low-warp high-strength copper foil, and raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the embodiment 1 is that raw material proportions of the electrolyte are different. A brightener is composed of SPS and PPS in a mass ratio of 1:3; a leveling agent is composed of PEI and polyethylene glycol (8000 in molecular weight) in a mass ratio of 1:1, and a smoothing agent is MBT.

[0112] Embodiment 5

[0113] The embodiment provides a preparation method of low-warp high-strength copper foil, and raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the embodiment 1 is that raw material proportions of the electrolyte are different. A brightener is composed of SPS and PPS in a mass ratio of 1:3; a leveling agent is composed of PEI and polyethylene glycol (8000 in molecular weight) in a mass ratio of 1:1, and a smoothing agent is MBT.

[0114] A copper foil warp test picture of the embodiment is shown in Table 1. Figure 2

[0115] Embodiment 6

[0116] The embodiment provides a preparation method of low-warp high-strength copper foil, and raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the embodiment 1 is that raw material proportions of the electrolyte are different. A brightener is composed of SPS and PPS in a mass ratio of 1:3; a leveling agent is composed of PEI and polyethylene glycol (8000 in molecular weight) in a mass ratio of 1:1, and a smoothing agent is MBT.

[0117] Embodiment 7

[0118] The embodiment provides a preparation method of low-warp high-strength copper foil, and raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the embodiment 1 is that raw material proportions of the electrolyte are different. A brightener is composed of SPS and PPS in a mass ratio of 1:2; a leveling agent is composed of PEI and polyethylene glycol (8000 in molecular weight) in a mass ratio of 3:1, and a smoothing agent is Kenagreen.

[0119] Embodiment 8

[0120] ​The embodiment provides a preparation method of a low-warp high-strength copper foil, raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the embodiment 1 is that the raw material proportions of the electrolyte are different. A brightener is composed of SPS and PPS in a mass ratio of 1:2; a walking agent is polyethylene glycol (molecular weight is 8000), and a leveling agent is MBT.

[0121] Comparative example

[0122] Comparative example 1

[0123] The comparative example provides a preparation method of a copper foil, raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the embodiment 1 is that the raw material proportions of the electrolyte are different. A brightener is composed of SPS and PPS in a mass ratio of 1:2; a walking agent is polyethylene glycol (molecular weight is 8000), and a leveling agent is MBT.

[0124] Comparative example 2

[0125] The comparative example provides a preparation method of a copper foil, raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the comparative example 1 is that the raw material proportions of the electrolyte are different.

[0126] Comparative example 3

[0127] The comparative example provides a preparation method of a copper foil, raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the comparative example 1 is that the raw material proportions of the electrolyte are different.

[0128] Comparative example 4

[0129] The comparative example provides a preparation method of a copper foil, raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the comparative example 1 is that the raw material proportions of the electrolyte are different.

[0130] Comparative example 5

[0131] The comparative example provides a preparation method of a copper foil, raw material components and proportions of an electrolyte are shown in Table 1, and the difference from the comparative example 1 is that the raw material proportions of the electrolyte are different. A brightener is composed of SPS and PPS in a mass ratio of 1:3; a walking agent is composed of PEI and polyethylene glycol (molecular weight is 8000) in a mass ratio of 1:1, and a leveling agent is MBT. A chelating agent is ethylenediaminetetraacetic acid.

[0132] Comparative example 6

[0133] The comparative example provides a preparation method of a copper foil, and the difference from the comparative example 1 is that the concentration of a chelating agent is 130 ppm.

[0134] Comparative example 7

[0135] The present comparative example provides a method for preparing a copper foil, which is different from Comparative Example 1 in that the chelating agent is 1,2,3-benzene propanetricarbazole.

[0136] Comparative Example 8

[0137] The present comparative example provides a method for preparing a copper foil, which is different from Comparative Example 1 in that no chelating agent is added.

[0138] Comparative Example 9

[0139] The present comparative example provides a method for preparing a copper foil, which is different from Comparative Example 1 in that no brightener is added.

[0140] Performance test

[0141] The copper foils prepared in Examples 1-8 and Comparative Examples 1-9 were tested for tensile strength and elongation, and the test results are shown in Table 2. Among them, the tensile strength and elongation were tested according to the test method of GB / T 29847-2013 "Test methods for copper foil for printed boards" using a HY-0230 universal material testing machine manufactured by Shanghai Hengyi Precision Instruments Co., Ltd. under the conditions of room temperature and strain speed of 50 mm / min. Generally, the sample was cut into a strip-shaped sample with a length and width of 100 and 12.7 mm, respectively, and five data were tested for each group of samples, and the average value was calculated as the final tensile strength or elongation.

[0142] Warpage test method: After aging and baking, a circular foil with a size of 100x100 mm was taken using a disc sampler, the copper foil was placed on a fixed platform with the rough surface facing up, and a steel ruler was used to measure the warpage (i.e. the maximum height of warpage). The baking time and warpage value are shown in Table 2.

[0143] Table 2 Performance test results of low-warp high-strength copper foils of Examples 1-8 and Comparative Examples 1-9

[0144]

[0145]

[0146] In combination with Examples 1-8 and Comparative Examples 1-9 and in combination with the data in Table 2, it can be seen that the copper foils prepared in Examples 1-8 have high tensile strength and elongation, warpage ≤10 mm, the ratio of the long and short axes of the grain fitting is small, and the OEE value of the pole piece is better. The higher the content of the chelating agent, the smaller the ratio of the long and short axes of the grain fitting, the more uniform the grain size, the lower the internal stress difference, the lower the warpage, and the higher the OEE efficiency of the pole piece process. However, when the content of the chelating agent exceeds the control range of 30-120 ppm, the ratio of the long and short axes of the grain fitting is too large, the internal stress is concentrated, and the warpage is >10 mm. At the same time, the brightener, the walking agent, and the leveling agent have a synergistic effect, which affects the grain structure and size of the copper foil and the elongation. When the addition amount of the chelating agent, the brightener, the walking agent, and the leveling agent is changed, it is easy to cause the anisotropy of the grain shape to be stronger, part of the stress to be concentrated, and the elongation to be <8%.

[0147] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical idea disclosed by the present application should be covered by the claims of the present application.

Claims

1. A low warpage high strength copper foil, characterized by: The copper foil has a warpage of less than or equal to 10 mm after being aged in an oven at 75-105 DEG C for 30-100 h.

2. The copper foil according to claim 1, characterized by: The copper foil has a thickness of 8 microns, a tensile strength of 500-700 MPa, and an elongation of greater than or equal to 6%.

3. The copper foil according to claim 1, characterized by: The cross section of the low-warpage ultra-high-strength copper foil has similar grain sizes and uniform distribution, and the ratio of the major axis to the minor axis of the fitting ellipse is Γ, which ranges from 1 to 10, and the calculation formula of Γ is as follows: wherein θ represents the sample inclination angle; ρ represents the correction coefficient, and the value range is 0.5-4.0; a and b represent the long radius and the short radius (microns) of the fitting ellipse, respectively.

4. A method of producing the low-warp high-strength copper foil according to any one of claims 1 to 3, characterized by, Said copper foil is prepared by electrolysis, said electrolysis employing an electrolyte comprising raw materials in the following mass concentrations: Cu 2+ 85-95 g / L, H2SO4110-115 g / L, Cl - 25-35 ppm, brightener 20-60 ppm, tracking agent 10-40 ppm, leveller 3-15 ppm, chelating agent 30-120 ppm, said chelating agent being DTPA-benzothiazole conjugate.

5. An additive for electrolytic copper foil for producing the copper foil as claimed in any one of claims 1 to 3, characterized in that, The additive is composed of a brightener, a walking agent, a leveling agent, and a chelating agent in a mass concentration ratio of 20-60:10-40:3-15:30-120; the chelating agent is a DTPA-benzothiazole conjugate.

6. The additive of claim 5, wherein: Further comprising one or more of the following features: A1) the DTPA-benzothiazole conjugate is selected from one or more of DTPA-benzothiazole, DTPA-2-amino benzothiazole, and DTPA-2-mercapto benzothiazole; A2) the brightener is a sulfur-containing compound; preferably, the brightener is selected from one or more of methylene dianaphthalene sulfonic acid sodium, polydithiopropane sulfonic acid sodium, methyl blue, 2-mercapto thiazoline, phenyl dithiopropane sulfonic acid sodium, polydithiodipropylene sulfonic acid sodium, or 3-mercapto propane sulfonic acid sodium; A3) the walking agent is a polyether compound; preferably, the walking agent is selected from one or more of polyethylene imine, polyethylene glycol, polypropylene glycol, or polyvinyl pyrrolidone; A4) the leveling agent is a nitrogen-containing amine organic compound; preferably, the leveling agent is selected from one or more of collagen, gelatin, gentian violet, 2-mercapto benzothiazole, tetrahydrothiazole thione, or isonicotinic acid.

7. An electrolyte solution for electrolytic copper foil for producing the copper foil according to any one of claims 1 to 3, characterized by: The electrolyte comprises the additive according to any one of claims 5-6, preferably the electrolyte comprises the following concentrations of raw materials: Cu 2+ 85-95 g / L, H2SO4110-115 g / L, Cl - 25-35 ppm, brightener 20-60 ppm, leveler 10-40 ppm, leveler 3-15 ppm, chelating agent 30-120 ppm, the chelating agent being DTPA-benzothiazole conjugate.

8. A current collector characterized by: The copper foil as claimed in any one of claims 1-3.

9. A pole piece characterized by: The current collector as claimed in claim 8; preferably, the equipment overall equipment effectiveness (OEE) during the coating preparation process is greater than or equal to 85%.

10. A secondary battery characterized by comprising: The pole piece as claimed in claim 9.

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