Surface-treated copper foil for lithium ion secondary battery, current collector, and lithium ion secondary battery

Abstract

The present disclosure provides a surface-treated copper foil for a lithium ion secondary battery, the surface-treated copper foil comprising a copper layer having a first surface and an opposing second surface, and nickel-containing treated layers respectively provided on the first surface and the second surface of the copper layer, the nickel adhesion amount of each treated layer being greater than or equal to 3.0 * 104 [mu] g / dm < 2 >, and the nickel adhesion amount of each treated layer being greater than or equal to 3.0 * 104 [mu] g / dm < 2 >. Each treatment layer provides a treatment surface having a chromaticity L * value of 30 to 60 and a protruding valley depth Svk of 0.10 to 0.65 [mu] m. The present disclosure further provides a current collector for a lithium ion secondary battery and a lithium ion secondary battery.

Description

Technical Field

[0001] The present disclosure relates to a surface-treated copper foil, and more particularly to a surface-treated copper foil for use in lithium-ion secondary batteries containing solid electrolytes. Background Art

[0002] Lithium-ion secondary batteries, due to their small size, high energy density, long life, rapid charging, minimal memory effect, and low cost, are widely used in various electronic devices, electric vehicles, and energy storage systems, making them indispensable in modern life. To achieve higher energy density and achieve high energy density in a small package, technologies to improve the performance of lithium-ion secondary batteries continue to develop and innovate.

[0003] Most lithium-ion secondary batteries on the market primarily use liquid electrolytes containing various organic compounds. However, these electrolytes are flammable and unstable at high temperatures. Therefore, solid-state batteries (SSBs), which are safer, more durable, faster to charge, and have higher capacity, have long been one of the most popular types of lithium-ion secondary batteries. Solid-state batteries utilize solid-state electrolytes (SSEs), which can be primarily classified into three categories: sulfides, oxides, and organic polymers. Sulfide solid electrolytes, with their high energy density, high ionic conductivity, low processing temperature, and good thermal stability, have attracted considerable attention due to their high development potential. However, these batteries are also difficult to manufacture, requiring extensive research to overcome the commercial challenges of large-scale production and application.

[0004] For example, solid-state batteries often use stainless steel as the negative electrode current collector material. However, stainless steel is difficult to thin, hindering battery miniaturization and thinning. Furthermore, stainless steel's conductivity is not high enough, far lower than that of copper. If copper were used as the negative electrode current collector material to improve conductivity, the copper could react with the sulfur in the solid electrolyte to form copper sulfide, increasing the battery's internal resistance, reducing cyclability, and raising battery temperatures, raising safety concerns and shortening the solid-state battery's lifespan.

[0005] Studies have shown that nickel is highly stable in air. Surface treatments such as nickel plating on copper foil, forming a thin protective film, can improve the foil's wear resistance, corrosion resistance, and rust resistance, making it chemically stable in batteries. However, while the nickel-plated protective layer has strong adhesion and resists detachment, the surface-treated copper foil is subject to multiple bends during the roll-to-roll production of lithium-ion secondary batteries, even at small angles near the core. This can cause cracks or creases in the nickel-plated protective layer, rendering it ineffective in protecting the copper foil from corrosion by the solid electrolyte. Summary of the Invention

[0006] In view of this, the present disclosure provides a surface-treated copper foil for lithium-ion secondary batteries with good processability and resistance to sulfide corrosion.

[0007] The surface-treated copper foil for lithium-ion secondary batteries disclosed herein comprises a copper layer and at least one treatment layer. The copper layer has a first surface and an opposite second surface. The treatment layer is formed on the first surface and / or the second surface of the copper layer, and the treatment layer contains nickel. The nickel adhesion amount of the treatment layer is ≥3.0×10 4 μg / dm 2 , wherein the treated layer provides a treated surface, the chromaticity L* value of the treated surface is 30 to 60 and the protruding valley depth Svk of the treated surface is 0.10 to 0.65 μm.

[0008] In one embodiment, the surface-treated copper foil comprises another treatment layer, each treatment layer being formed on the first surface and the second surface of the copper layer, respectively.

[0009] In one embodiment, the nickel deposition amount of each treatment layer of the surface treated copper foil is 3.0×10 4 to 21.5×10 4 μg / dm 2 .

[0010] In one embodiment, the nickel deposition amount of each treatment layer of the surface treated copper foil is 4.0×10 4 to 20.0×10 4 μg / dm 2 .

[0011] In one embodiment, the nickel deposition amount of each treatment layer of the surface treated copper foil is 4.5×10 4 to 18.5×10 4 μg / dm 2 .

[0012] In one embodiment, the depth Svk of the protruding valleys on the treated surface of the surface-treated copper foil is 0.10 to 0.45 μm.

[0013] In one embodiment, the chromaticity a* value of the treated surface of the surface-treated copper foil is from -5 to 5.

[0014] In one embodiment, the chromaticity b* value of the treated surface of the surface-treated copper foil is -5 to 5.

[0015] In one embodiment, the conductivity of the surface treated copper foil is ≥3.2×10 7 S / m.

[0016] In one embodiment, the copper layer of the surface-treated copper foil is an electrolytic copper foil or a rolled copper foil.

[0017] The present disclosure also provides a current collector for a lithium ion secondary battery, comprising the surface-treated copper foil described in the present disclosure.

[0018] The present disclosure also provides a lithium ion secondary battery comprising the current collector described in the present disclosure. In one embodiment, the lithium ion secondary battery comprises a solid electrolyte.

[0019] The present invention controls the nickel adhesion amount of the surface-treated copper foil treatment layer, the chromaticity L* value of the treatment surface, and the protruding valley depth Svk within a specific range, thereby improving the problem of cracks in the surface-treated layer after bending, and making the surface-treated copper foil have corrosion resistance.

[0020] The foregoing summary is not intended to represent every specific embodiment or every aspect of the present disclosure. Rather, the foregoing summary only provides examples of the novel aspects and features of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Embodiments of the present invention are described by way of example with reference to the accompanying drawings.

[0022] Figure 1 Schematic diagram of the process for preparing green foil and nickel plating process according to the present disclosure.

[0023] Figure 2-1 Schematic diagram of the bending crack testing method disclosed herein.

[0024] Figure 2-2 Scanning electron microscopy (SEM) showed no cracks in the nickel plating.

[0025] Figure 2-3 Scanning electron microscope (SEM) images show cracks in the nickel plating.

[0026] Figure 3 2 is a comparison diagram of the surface treated copper foil disclosed in the present invention before and after corrosion resistance test under a scanning electron microscope (SEM).

[0027] Main component symbols

[0028] 1 roller

[0029] 2 Anode plate

[0030] 3 Electrolyte

[0031] 4 copper layers

[0032] 4a Roller surface

[0033] 4b Sedimentary surface

[0034] 5. Electroplating solution

[0035] 6-electrode plate

[0036] 7 Air Knife

[0037] 91 PVC pipe

[0038] 92 weights. DETAILED DESCRIPTION

[0039] The following describes the embodiments of the present disclosure through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present disclosure from the contents described herein.

[0040] It should be noted that all ranges and values ​​herein are inclusive and combinable. If a numerical range is provided, every value between and including the upper and lower limits of the range is deemed to be disclosed herein. It should be understood that any numerical range cited herein is intended to include all subranges encompassed by that range. For example, a range of "1 to 10" is intended to include all subranges between and including the stated minimum value of 1 and the maximum value of 10; in other words, having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10. Because the disclosed numerical ranges are continuous, they include every value between the minimum and maximum values.

[0041] When used herein, the terms "comprise," "include," "contain," or "have" specific elements, unless otherwise specified, may also include other elements, components, structures, regions, parts, devices, systems, steps, or connections, and do not exclude such other elements. In other words, when a claimed invention "comprises," "includes," "contains," or "has" specific elements, it actually allows for other unspecified elements, whether or not such elements are essential.

[0042] The terms "upper" and "lower" described herein are only used to illustrate specific embodiments of the present invention and are not intended to limit the scope of the present invention. Adjustments, interchanges, and changes in their relative positions and relationships, without substantially changing the technical content of the present invention, should be considered within the scope of the present invention.

[0043] Unless otherwise expressly stated herein, the singular forms "a", "an" and "the" herein include plural forms as well, and "or" and "and / or" herein are used interchangeably.

[0044] The surface treated copper foil disclosed in the present invention is a copper layer subjected to surface treatment, so the surface treated copper foil at least comprises a copper layer and a treatment layer thereon. This copper layer refers to a raw foil (bare copper foil), and the raw foil can be a rolled copper foil or an electrolytic copper foil. The raw foil is essentially composed of copper (for example, >99wt% copper). At least one of the first surface and the opposite second surface of the raw foil is surface treated, such as by coating, and both the first surface and the second surface need to be surface treated. The treatment layer provides ≥3.0×10 4 μg / dm 2 The treated layer provides a treated surface, and the chromaticity L* value of the treated surface is 30 to 60, and the depth Svk of the protruding valley of the treated surface is 0.10 to 0.65 μm.

[0045] In some embodiments, the raw foil can be made by electrodeposition (also known as electrolysis, electrolytic deposition, or electroplating) using a foil making machine to provide a raw foil having a roll surface and a deposition surface. Figure 1 As shown, a foil making machine may include at least a roller 1 serving as a cathode, a pair of insoluble metal anode plates 2, and an electrolyte 3 and its feed pipe (not shown). Roller 1 is a rotatable metal roller with a mirror-polished surface. The metal anode plates 2 can be detachably fixed to the lower half of the roller to surround the lower half of the roller. The feed pipe can be fixed directly below roller 1 and located between the two metal anode plates 2. Roller surface 4a of copper layer 4 is the surface of copper layer 4 that contacts roller 1 during the electrodeposition process; deposition surface 4b is the opposite side of roller surface 4a, or the surface of copper layer 4 that contacts electrolyte 3 during the electrodeposition process to form copper layer 4. The method for producing raw foil includes partially immersing the rotating roller 1 in electrolyte 3 containing copper ions. Therefore, under the action of an electric current, copper ions are attracted to roller 1 and reduced, resulting in copper metal plating on the surface of roller 1 and forming an electrolytic copper layer 4 on the surface of roller 1. In a continuous process, the copper layer 4 is removed by rotating the roller 1 and rotating the formed copper layer 4 out of the electrolyte 3 along with the roller 1. For example, in a continuous process, the copper layer 4 can be pulled away from the roller 1 as it is formed and passed over or through the roller. In one embodiment, the roller surface 4a corresponds to the first surface, and the deposition surface 4b corresponds to the second surface.

[0046] To meet the battery's high capacitance requirements, the copper layer should be minimally thick. In some embodiments, the raw foil thickness can be 4 to 10 μm. The surface topography of the raw foil can affect the morphology of the treated layer. In some embodiments, a raw foil with a protruding valley depth Svk of 1 μm or less can be selected for the copper layer.

[0047] The surface treated copper foil of the present invention is obtained by subjecting the raw foil to surface treatment, so that the surface treated copper foil includes a treatment layer located on the first or second surface in addition to the raw foil. The treatment layer contains nickel, which can protect the raw foil from degradation such as due to corrosion. The nickel-containing treatment layer can be prepared by any known method, including immersing the formed raw foil in or passing through a solution containing nickel, or plating nickel metal (for example, by an electroplating bath) on the formed raw foil. The process can be continuous and part of the overall process for preparing the surface treated copper foil. The treatment layer can optionally be provided in two layers, formed on the first surface and the second surface respectively, or can be formed on only one side, depending on the needs of the application. For example, the surface treated copper foil in a button-type battery only has one side that contacts the electrolyte, so it is only necessary to form a treatment layer on this side to prevent the surface treated copper foil from corrosion.

[0048] The present disclosure found that the amount of nickel attached affects the performance of the surface treated copper foil. Nickel oxidizes slowly at room temperature and is generally considered to have corrosion resistance. Its atomic size (0.125nm) is close to that of copper (0.128nm), and the nickel atoms are stacked in a face-centered cubic (FCC) stacking like copper, which makes it have good atomic matching with copper. However, nickel has poor electrical conductivity, much lower than copper. Therefore, if the nickel attachment is too low, for example, less than 30,000μg / dm 2 , has little effect on conductivity, but has poor corrosion resistance and risks of copper layer being corroded by sulfides, which increases the internal resistance of the battery, increases the battery temperature, reduces the charge and discharge efficiency, and increases the risk of solid-state battery failure and thermal runaway. 2 , which effectively prevents the copper layer from being corroded by sulfides. Furthermore, when the aforementioned adhesion amount is achieved, the surface-treated copper foil also exhibits resistance to oxidation, making it suitable for use in solid-state batteries using high-temperature processes, such as oxide-type solid electrolyte batteries.

[0049] Increasing the nickel content can improve corrosion resistance, but it will also reduce the conductivity of the surface-treated copper foil, resulting in an increase in the internal resistance of the battery, which in turn reduces the battery charge and discharge speed. Therefore, to control the conductivity of the surface-treated copper foil, the nickel content needs to be controlled to less than or equal to 215,000 μg / dm 2 In the present disclosure, the nickel content of the nickel-containing treatment layer of the surface treated copper foil is controlled to be 30,000 to 215,000 μg / dm 2 The surface-treated copper foil can have sufficient corrosion resistance to sulfides while maintaining satisfactory electrical conductivity. After the nickel-containing treatment layer is provided on the raw foil, the total thickness of the surface-treated copper foil of the present disclosure is approximately 4.3 μm or greater, for example, 4.3 μm to 16 μm, or 5 μm to 15 μm, but is not limited thereto.

[0050] Among the means for regulating the nickel deposition amount of the surface treated copper foil treatment layer, there can be cited the regulation by adjusting the electroplating time, current density and temperature of the nickel plating solution. In one embodiment, the electroplating time of nickel plating is 100 to 600 seconds, for example, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550 and 600 seconds. In one embodiment, the current density of nickel plating is 5 to 20 A / dm 2 , such as 5, 10, 15 and 20A / dm 2 In one embodiment, the nickel plating temperature is 40 to 60°C, such as 40, 45, 50, 55 and 60°C.

[0051] In one embodiment, the nickel deposition amount of each treatment layer of the surface treated copper foil is 3.0×10 4 Up to 3.0x10 4 to 21.5x 10 4 μg / dm 2 , 4.0x 10 4 to 20.0x10 4 μg / dm 2 , or 4.5x 10 4 to 18.5x 10 4 μg / dm 2 , for example, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, 100,000, 110,000, 120,000, 130,000, 140,000, 150,000, 160,000, 170,000, 180,000, 190,000, 200,000 and 210,000 μg / dm 2 , and any value between the values ​​listed above.

[0052] As used herein, "chromaticity" refers to the CIE color space, also known as L*a*b*, which is defined by the International Commission on Illumination (CIE) and is an internationally accepted color measurement standard. The CIE color space expresses color as three values: "L*" represents the lightness of the color, with an L* value of 0 defining black and 100 indicating white. In other words, the larger the L* value, the whiter it is, and the smaller the L* value, the blacker it is. "a*" represents the position between red / magenta and green in human vision, with a positive a* value indicating a reddish / magenta color and a negative a* value indicating a greenish color. "b*" represents the position between blue and yellow in human vision, with a positive b* value indicating a yellowish color and a negative a* value indicating a bluish color. The CIE color space is the most complete color model that can be used to describe all colors visible to the human eye, where the three values ​​of L*, a*, and b* can be used to detect subtle differences in similar colors. Herein, L* value, a* value, and b* value are in accordance with JIS Z 8729 and can be obtained by measuring the values ​​using a spectrocolorimeter based on the method described in JIS Z 8722.

[0053] The present disclosure discovered that the colorimetric L* value indicates the surface properties of surface-treated copper foil. If the L* value of the surface-treated copper foil is between 65 and 80, cracks may appear on the surface after bending. Therefore, during roll-to-roll bending processes, the nickel-plated layer cannot properly protect the copper layer, causing the copper layer to come into contact with the solid-state electrolyte and causing solid-state battery failure. In the present disclosure, by controlling the L* value of the treated surface of the surface-treated copper foil to within the range of 30 to 60, the problem of cracks on the nickel-plated copper layer after bending can be alleviated.

[0054] Among the means for regulating the L* value of the treated surface of the surface treated copper foil, the regulation can be listed as adjusting the total organic carbon (TOC) concentration, electroplating time, current density and temperature in the nickel plating solution. In one embodiment, the total organic carbon concentration can be achieved by the concentration of additives, such as brighteners. In one embodiment, the brightener can be saccharin and / or polyethylene glycol (PEG), and the content can be 30 to 100 ppm. In one embodiment, the brightener is saccharin and PEG in a 1:1 ratio. In one embodiment, the electroplating time of nickel plating is 100 to 600 seconds. In one embodiment, the current density of nickel plating is 5 to 20A / dm 2 In one embodiment, the nickel plating temperature is 40 to 60°C.

[0055] In one embodiment, the chromaticity L* value of the treated surface of the surface-treated copper foil is in the range of 30 to 60, for example, 30, 35, 40, 45, 50, 55 and 60, and any value therebetween.

[0056] In one embodiment, the chromaticity a* value of the treated surface of the surface treated copper foil is in the range of -5 to 5, for example, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4 and 5, and any value in between the above listed values.

[0057] In one embodiment, the chromaticity b* value of the treated side of the surface treated copper foil is in the range of -5 to 5, for example, -5, -4, -3, -2, -1, 0, 1, 2, 3, 4 and 5, and any value in between the above listed values.

[0058] As used herein, "valley depth" and "Svk" are equivalent terms used to describe a surface profile and represent the average depth of the valleys below the core in the surface profile. Valley depth Svk is based on ISO 25178-2:2012 and can be measured using a laser microscope.

[0059] The present disclosure found that the pits on the surface of the surface-treated copper foil (related to the protruding valley depth Svk) will affect the bending resistance of the surface-treated copper foil, as well as the adhesion and coating uniformity of the negative electrode material. From the perspective of bending resistance, it is speculated that if the protruding valley depth Svk value is too small, the overly smooth surface has a poor ability to withstand tensile stress, and when bent, due to the large deformation amplitude of the outer edge of the bend, it is easy to produce cracks or even break at the bend; on the contrary, if the protruding valley depth Svk value is too large, the pits on the surface of the surface-treated copper foil are too deep, and the mechanical strength of the pits is insufficient, and cracks are also easy to appear after being bent. In the present disclosure, by regulating the protruding valley depth Svk value of the surface of the surface-treated copper foil (i.e., the treated surface) to be in the range of 0.10 to 0.65 μm, the problem of cracks in the surface-treated copper foil after bending can be improved. As for coating uniformity, if the protruding valley depth Svk value is too large, the negative electrode material will be unevenly coated, for example, too much deposition will occur in the pits; if the protruding valley depth Svk value is controlled within an appropriate range, for example, within 0.65μm, the negative electrode material coating uniformity is good, and if it is further controlled within 0.45μm, the negative electrode material coating uniformity is even better.

[0060] Among the methods for regulating the protruding valley depth Svk value of the surface-treated copper foil, one can cite the regulation of the total organic carbon (TOC) concentration in the nickel plating solution, the electroplating time, the current density, and the temperature. In one embodiment, the total organic carbon concentration can be achieved through additives, such as brighteners. Adding brighteners during the electroplating process can improve the porosity, brightness, dispersibility of the plating solution, and the deep plating ability of the coating. Brighteners are generally stable and can provide high ductility over a wide current density range, making the deposited metal layer bright, flat, and ductile. Brighteners include, but are not limited to, metal salts, 2-butyne-1,4-diol, saccharin, condensation products of epoxy compounds, pyridine derivatives, alkynylamine compounds, and propargyl alcohol derivatives. In one embodiment, the brightener is saccharin and / or polyethylene glycol (PEG). In one embodiment, the brightener is a 1:1 ratio of saccharin and PEG. In one embodiment, the brightener concentration is 30 to 100 ppm. In one embodiment, the nickel plating time is 100 to 600 seconds. In one embodiment, the nickel plating current density is 5 to 20A / dm 2 In one embodiment, the nickel plating temperature is 40 to 60°C.

[0061] In one embodiment, the depth Svk of the protruding valley of the treated surface of the surface-treated copper foil is in the range of 0.10 to 0.65 μm, for example, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60 and 0.65 μm, and any value in between the above-listed values.

[0062] In one embodiment, the conductivity of the surface treated copper foil is ≥3.2x10 7 S / m.

[0063] In one embodiment, the surface-treated copper foil can be used as a current collector in a battery, such as a lithium-ion secondary battery. The current collector can be a positive electrode current collector and / or a negative electrode current collector. In one embodiment, the battery is a laminate structure, for example, including a copper negative electrode current collector, a negative electrode active material, a separator, a positive electrode active material, and a positive electrode current collector. The active material is coated on at least one side of the surface-treated copper foil of the present disclosure. For example, the active material may include, but is not limited to, materials containing carbon, silicon, germanium, and combinations or mixtures thereof.

[0064] The present disclosure also provides a lithium ion secondary battery comprising the current collector of the present disclosure.

[0065] The electrolyte of the lithium-ion secondary battery of the present disclosure may include a solid electrolyte. The solid electrolyte may be a crystalline electrolyte, a glass electrolyte, a glass ceramic electrolyte, or a polymer electrolyte, but is not limited thereto. Specifically, the crystalline electrolyte may be a sulfide solid electrolyte such as a lithium superion conductor (LISICON) type or an argyrodite type; or an oxide solid electrolyte such as a garnet structure type, a perovskite structure type, a NASICON structure type, but is not limited thereto. The glass electrolyte may be a glassy solid electrolyte such as an oxide or a sulfide, but is not limited thereto. The polymer electrolyte may be a pure solid polymer electrolyte such as polyethylene oxide (PEO) or polypropylene oxide (PPO); or a colloidal polymer electrolyte such as polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), or polyvinylidene fluoride (PVDF). However, the present invention is not limited thereto.

[0066] The surface-treated copper foil in the embodiments described herein can be used in devices, such as any item or component that requires electricity to operate. For example, independent, separate, and mobile components and devices require small and light batteries. Such devices may include, but are not limited to, vehicles (e.g., cars, trams, buses, trucks, ships, submarines, airplanes), computers (e.g., microcontrollers, laptops, tablets), phones (e.g., smartphones, wireless phones), personal health monitoring and maintenance equipment (e.g., blood glucose monitors, pacemakers), tools (e.g., electric drills, electric saws), lighting devices (e.g., flashlights, emergency lighting, signs), handheld measuring devices (e.g., pH meters, air monitoring devices), and living units (e.g., in spacecraft, trailers, houses, airplanes, submarines).

[0067] In one embodiment, the lithium-ion secondary battery can be a stacked lithium-ion secondary battery comprising a negative electrode and a positive electrode stacked with a separator, or a spirally wound stacked lithium-ion secondary battery comprising a continuous electrode and a separator spirally wound together, but is not limited thereto. Depending on the application device, the lithium-ion secondary battery of the present disclosure can be manufactured into, for example, a laminated secondary battery, a cylindrical secondary battery, a prismatic secondary battery, a pouch-shaped secondary battery, or a button-shaped secondary battery, but is not limited thereto.

[0068] The following examples further illustrate the details. However, the interpretation of this disclosure should not be limited to the following examples. It should be understood that within the scope of this disclosure, the technical features mentioned above and below (such as the embodiments) can be freely combined with each other to form new or preferred technical solutions, which are omitted for brevity.

[0069] Examples and Comparative Examples

[0070] A. Preparation of Raw Foil

[0071] The electrolyte was prepared by dissolving copper wire in a 50 wt% aqueous sulfuric acid solution to obtain a copper sulfate electrolyte containing 320 g / L copper sulfate (CuSO4·5H2O) and 85 g / L sulfuric acid. The chloride ion concentration in the copper sulfate electrolyte was 35 ppm.

[0072] The raw foil is prepared by electrodeposition on a rotating roller, which is partially immersed in the above copper sulfate electrolyte. The roller acts as a cathode opposite the anode electrode, causing the copper ions in the electrolyte to be deposited on the roller in a continuous manner. 2 The current density was set at 1000 nm and the temperature of the electrolyte was controlled at 48° C. to prepare a green foil having a thickness of 4 to 10 μm.

[0073] B. Nickel plating

[0074] Next, a plating solution containing 350 g / L nickel sulfate (NiSO4), 80 g / L boric acid and 15 g / L sodium hypochlorite was prepared, wherein the chloride ion concentration was 15 ppm and the brightener (saccharin:PEG=1:1) concentration was 10 to 300 ppm.

[0075] like Figure 1 As shown, the raw foil is transported to the nickel plating device through a series of guide rollers for nickel plating. The raw foil is immersed in a treatment tank containing the above-mentioned electroplating solution 5, and a nickel plating layer is formed on the first and second surfaces of the raw foil by electrodeposition using two sets of electrode plates 6. A 5 to 30A / dm 2 The current density is adjusted to 20 to 80° C., and the temperature of the plating solution is controlled to be 20 to 80° C., and the electroplating time is 60 to 600 seconds to prepare a nickel-plated surface-treated copper foil.

[0076] After the nickel plating is complete, the nickel-plated copper foil is guided to a series of guide rollers. Excess plating solution and other substances on the surface are removed using an air knife 7. The foil is then dried and rolled up to obtain the surface-treated copper foil. The parameters for preparing the surface-treated copper foil are shown in Table 1 below.

[0077] Table 1

[0078]

[0079]

[0080] C. Testing

[0081] (I) Chromaticity (CIE L*a*b*)

[0082] The surface-treated copper foils prepared in Examples and Comparative Examples were subjected to colorimetric analysis to measure the L* value, a* value, and b* value of the surface-treated copper foils.

[0083] Standard: L* value, a* value, b* value color system described in JIS Z 8729 (2004)

[0084] Instrument: Spectrophotometer (Konica-Minolta; CM2500c); measured values ​​are based on the method of JIS Z 8722 (2000)

[0085] Lighting / receiving system: 45 / 0 (45° ring lighting, vertical receiving)

[0086] Observation angle (observer): 2°

[0087] Wavelength range: 360~740nm

[0088] Wavelength spacing: 10nm

[0089] Reflectivity range: 0~175%; resolution 0.01%

[0090] Measuring time: 1.5 seconds

[0091] Measuring / illumination aperture: Φ7mm / Φ11mm

[0092] Light source (illumination body): D65 daylight

[0093] (II) Depth of protruding valley Svk

[0094] Surface profile analysis was performed on the surface-treated copper foils prepared in Examples and Comparative Examples to measure the protruding valley depths Svk of the surface-treated copper foils.

[0095] Standard: ISO 25178-2 (2012)

[0096] Instrument: Laser microscope (LEXT OLS5000-SAF, Olympus)

[0097] Light source wavelength: 405nm

[0098] Objective lens magnification: 100x objective lens (MPLAPON-100x LEXT, Olympus)

[0099] Optical zoom: 1.0x

[0100] Observation area: 129 μm × 129 μm

[0101] Resolution: 1024 pixels × 1024 pixels

[0102] Condition: Enable the automatic tilt removal function of the laser microscope (Auto tilt removal)

[0103] Filter: Unfiltered

[0104] Air temperature: 24±3℃

[0105] Relative humidity: 63±3%

[0106] (III) Nickel adhesion

[0107] The surface-treated copper foils prepared in Examples and Comparative Examples were subjected to inductively coupled plasma (ICP) analysis to measure the nickel adhesion amount of the surface-treated copper foils.

[0108] Sample preparation:

[0109] Cut the surface treated copper foil into 150×150mm size, stick tape on one side of the surface treated copper foil to prevent the surface from dissolving, and then cut the surface treated copper foil into 100×100mm (area = 1dm 2 ) size as test samples.

[0110] Place 20 mL of 18% HCl in a square container with a base length of 120 x 120 mm. Immerse the sample in the container, with the tape side of the sample at the bottom. Shake the container continuously from side to side during immersion, approximately 5 cm to the left and 5 cm to the right (one shake counts), at a frequency of 6 shakes per minute.

[0111] After soaking for 7.5 minutes, add 2 mL of 30% hydrogen peroxide solution to the square container. Continue shaking as described above until the nickel layer on the side not protected by the tape is completely dissolved, revealing the original color of the surface-treated copper foil. Then, remove the sample. Pour the solution into a 50 mL volumetric flask and fill to 50 mL with deionized water.

[0112] Analysis: The nickel content of the aforementioned 50 mL solution was determined using an inductively coupled plasma optical emission spectrometer (ICP-AES) with argon as the carrier gas and a nebulizer flow rate of 0.5 L / min.

[0113] Instrument: Thermo Scientific TM iCAP TM 7400 ICP-OES Duo MFC

[0114] (IV) Bending cracks

[0115] Test whether cracks and creases are generated on the copper foils with various surface treatments after bending.

[0116] Test method: Figure 2-1 As shown, a surface-treated copper foil sample measuring 80 mm (TD) x 200 mm (MD) was taken and a PVC tube 91 with a nominal diameter of 1 / 2" (outer diameter 22 mm) was used. The sample was first bent from the front side. A 100 g weight 92 was applied to each end of the surface-treated copper foil for 10 seconds. The sample was then bent from the back side. Each bending cycle counted as one, for a total of 10 cycles. The surface condition of the nickel coating was then observed using a scanning electron microscope (SEM) at 800x magnification. No cracks were observed. Figure 2-2 As shown;

[0117] The result of cracks is Figure 2-3 shown.

[0118] (V) Negative electrode material coating uniformity

[0119] The negative electrode material coating uniformity of each surface-treated copper foil was tested. The negative electrode materials, test methods, and test standards used are shown below.

[0120] The negative electrode material was prepared by using water as a solvent and having a liquid-to-solid ratio of 73% (100 g of negative electrode material: 73 g of water) as listed in the table below.

[0121]

[0122] After mixing the components of the negative electrode material formula, the negative electrode material was coated on the surface of the surface-treated copper foil at a speed of 5 meters per minute to a thickness of 200 microns, and then dried in an oven at 120°C for 1 hour. Subsequently, a press was used to press the negative electrode (surface-treated copper foil + negative electrode material). The roller size of the press was φ250mm×250mm, its hardness was 62 to 65HRC, and the material of the roller was high carbon chromium bearing steel (SUJ2). A pressing (calendering) speed of 1m / min and a pressure of 3000psi were used to press to produce the negative electrode.

[0123] Cut the negative electrode into multiple test pieces of 50 x 50 mm in size. Take 10 test pieces in total and weigh them with an electronic balance to confirm the deviation of each weight value from the weight average.

[0124] The weight deviation is less than 0.3% and is considered extremely uniform (◎).

[0125] Weight deviation of 0.3 to 0.5% is uniform (○);

[0126] Weight deviation of 0.5-1.5% is considered uneven (Δ);

[0127] A weight deviation exceeding 1.5% was considered extremely non-uniform (X).

[0128] (VI) Conductivity

[0129] The electrical conductivity of each surface-treated copper foil was tested using the following test methods, standards, and parameters:

[0130] Method: Use the four-probe method to measure the conductivity of any three parts. Calculate the conductivity value of the surface-treated copper foil from the measured surface resistance, and take the arithmetic average of the conductivity values ​​of the three parts as the conductivity value.

[0131] Standard: IPC TM650 2.5.14

[0132] Instrument: LRS4-TG2 (KeithLink)

[0133] Probe diameter: 100 μm

[0134] Needle pitch: 1.6mm

[0135] Pressure: 100g

[0136] Volume resistivity conversion factor: 4.532

[0137] Sample size: 100mm x 100mm

[0138] Ambient temperature: 25℃

[0139] (VII) Sulfur corrosion resistance (FoS)

[0140] The sulfur corrosion resistance of the copper foils with various surface treatments was tested using the following test methods.

[0141] Method: Typical wet sulfur vapor test method where the sample is exposed to sulfur vapor

[0142] Standard: ASTM B809-95

[0143] The surface morphology of the surface-treated copper foil was first observed using a scanning electron microscope (SEM).

[0144] After the surface-treated copper foil is subjected to the bending crack test, a 50 mm x 50 mm sample is cut.

[0145] Nitrogen pre-baking: Place the sample in a nitrogen oven at 50°C for 24 hours (nitrogen inlet pressure 10 psi, nitrogen flow rate 1 liter / minute) to prevent the generation of organic volatile gases during the test from affecting the FoS test results.

[0146] Place excess sulfur in a sealed glass container, and hang the sample in the aforementioned glass container and maintain the temperature at 50°C and relative humidity at 82%. Expose the sample to a saturated sulfur vapor environment and take it out after maintaining it for 24 hours.

[0147] like Figure 3 As shown, the surface morphology of the copper foil treated with wet sulfur vapor test was confirmed by scanning electron microscopy (SEM). If copper sulfide particles appeared on the surface, it was considered unqualified.

[0148] The results of the chromaticity (L*a*b*), protruding valley depth Svk, nickel adhesion, whether there are cracks after bending, coating uniformity, conductivity and corrosion resistance of each surface treated copper foil obtained by the above test method are listed in Table 2 below.

[0149] Table 2

[0150]

[0151]

[0152] The above results demonstrate that the surface-treated copper foil disclosed herein, by controlling the nickel deposition, chromaticity L* value, and protruding valley depth Svk of the treated layer, can alleviate surface cracking after bending and exhibit excellent corrosion resistance. Furthermore, the surface-treated copper foil disclosed herein exhibits good coating uniformity when coated with negative electrode materials.

[0153] Specifically, according to corrosion resistance tests, the surface-treated copper foils of Examples 1 to 16 of the present disclosure exhibited a protective effect by controlling the nickel deposition, chromaticity L* value, and protruding valley depth Svk of the treatment layer, thereby achieving good corrosion resistance. In contrast, the surface-treated copper foils of Comparative Examples 1 to 9 had poor protection and corrosion resistance due to the treatment layer, resulting in copper sulfide reacting with wet sulfur vapor on the surface. According to a bending crack test, excessively high or low chromaticity L* values ​​and protruding valley depth Svk can easily cause the surface-treated copper foil to crack after bending. However, controlling the chromaticity L* value within a suitable range, such as between 30 and 60, and the protruding valley depth Svk within a suitable range, such as between 0.10 and 0.65 μm, can make the treatment layer stable to bending and less prone to cracking. According to the negative electrode material coating uniformity test, the higher the protruding valley depth Svk is, the worse the coating uniformity is. When the protruding valley depth Svk is greater than 0.65 μm, the negative electrode material coating is uneven.

[0154] In addition, it can be found from the above results that the nickel adhesion of the treatment layer affects the conductivity of the surface treated copper foil. If the nickel adhesion is too high, for example, the nickel adhesion in Examples 15 and 16 is higher than 21.5 x 10 4 μg / dm 2Therefore, the nickel adhesion of the treatment layer is controlled within a suitable range, for example, 3.0x10 4 to 21.5x10 4 μg / dm 2 , which can further improve the conductivity.

[0155] Furthermore, the above results also show that the negative electrode material coating uniformity can be further improved by adjusting the protrusion valley depth Svk. For example, when the protrusion valley depth Svk is within 0.65 μm, the negative electrode material coating uniformity has already met the requirements. However, if the protrusion valley depth Svk is further controlled within 0.45 μm, the negative electrode material coating uniformity is further improved.

Claims

1. A surface-treated copper foil for a lithium-ion secondary battery, comprising: a copper layer having a first surface and an opposing second surface; and A treatment layer is formed on the first surface or the second surface of the copper layer, wherein The treatment layer contains nickel, Wherein, the nickel adhesion amount of the treatment layer is ≥3.0×10 4 μg / dm 2 , The treated layer provides a treated surface, the chromaticity L* value of the treated surface is 30 to 60, and the depth Svk of the protruding valley of the treated surface is 0.10 to 0.65 μm.

2. The surface-treated copper foil according to claim 1, wherein The surface-treated copper foil includes another treatment layer, and each of the treatment layers is formed on the first surface and the second surface of the copper layer, respectively.

3. The surface-treated copper foil according to claim 1, wherein The nickel adhesion of the treatment layer is 3.0×10 4 to 21.5×10 4 μg / dm 2 .

4. The surface-treated copper foil according to claim 1, wherein The nickel adhesion of the treatment layer is 4.0×10 4 to 20.0×10 4 μg / dm 2 .

5. The surface-treated copper foil according to claim 1, wherein The nickel adhesion of the treatment layer is 4.5×10 4 to 18.5×10 4 μg / dm 2 .

6. The surface-treated copper foil according to claim 1, wherein The depth Svk of the protruding valley of the processed surface is 0.10 to 0.45 μm.

7. The surface-treated copper foil according to claim 1, wherein The chromaticity a* value of the treated surface is -5 to 5.

8. The surface-treated copper foil according to claim 1, wherein The chromaticity b* value of the treated surface is -5 to 5.

9. The surface-treated copper foil according to claim 1, wherein The electrical conductivity of the surface treated copper foil is ≥3.2×10 7 S / m.

10. The surface-treated copper foil according to claim 1, wherein The copper layer is electrolytic copper foil or rolled copper foil. 11 . A current collector for a lithium ion secondary battery, comprising the surface-treated copper foil according to claim 1 . 12 . A lithium ion secondary battery comprising the current collector according to claim 11 .

13. The lithium ion secondary battery according to claim 12, wherein The lithium-ion secondary battery includes a solid electrolyte.

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