Graphene oxide coated copper current collector and method for manufacturing the same

Abstract

To solve a problem in which a lithium ion battery (LIB) using a silicon negative electrode undergoes a large volume change during charging and discharging, and peeling occurred between a negative electrode material and a copper current collector, which has an adverse effect on its cycle characteristics.SOLUTION: A graphene oxide coated copper current collector can maintain its capacity well even after repeated discharges by increasing the physical interaction between a copper current collector and a negative electrode material by coating the copper current collector with graphene oxide, and can improve the cycle characteristics of an LIB using a silicon negative electrode.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a graphene-coated copper current collector for a lithium-ion battery (LIB) and a method for manufacturing the same. More specifically, the present invention relates to a graphene-coated copper current collector that improves the cycle characteristics of an LIB and a method for manufacturing the same.

Background Art

[0002] LIBs are widely used in electric vehicles, smartphones, etc., and there is a continuous demand for further capacity increase and improvement of battery life (cycle characteristics). Among them, as next-generation LIBs, LIBs using a silicon negative electrode have been developed. The silicon negative electrode is known to have a higher capacity compared to the current graphite-based negative electrode. For the silicon negative electrode, a silicon-based material as an active material, a carbon-based material such as carbon black or carbon nanotubes as a conductive assistant, and a polymer material such as styrene-butadiene rubber (SBR) as a binder are mixed and used. Also, a metal material such as copper is used as a current collector.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0004]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In lithium-ion batteries (LIBs) using silicon anodes, a problem has been that large volume changes during charging and discharging cause delamination between the anode material and the copper current collector, negatively impacting cycle characteristics. As a solution to this problem, methods such as improving the strength of the copper current collector itself are being investigated (Non-Patent Literature 1). Furthermore, while Patent Documents 1 and 2 disclose coating with graphene other than graphene oxide, graphene is highly hydrophobic and therefore insufficient in terms of ensuring close contact between the copper current collector and the negative electrode material (especially the organic component). In view of the above circumstances, the present invention provides a graphene oxide-coated copper current collector that can maintain good capacity even after repeated discharges by coating the copper current collector with graphene oxide, thereby enhancing the physical interaction between the copper current collector and the negative electrode material, and improving the cycle characteristics of a LIB using a silicon negative electrode. [Means for solving the problem]

[0006] The inventors of this invention conducted various studies to achieve the above objectives and arrived at the present invention. In other words, the present invention relates to a graphene oxide-coated copper current collector for lithium-ion batteries, characterized in that the surface of the copper current collector is coated with graphene oxide, and to a method for manufacturing the same. [Effects of the Invention]

[0007] By using the graphene oxide-coated copper current collector and its manufacturing method according to the present invention, it is possible to improve the LIB cycle characteristics. [Modes for carrying out the invention]

[0008] The present invention will be described in detail below. Furthermore, combinations of two or more of the individual preferred embodiments of the present invention described below are also preferred embodiments of the present invention.

[0009] [Graphene oxide and graphene oxide dispersion] The graphene oxide of the present invention is obtained by oxidizing and exfoliating graphite. The method for producing graphene oxide is not particularly limited, but for example, graphite is oxidized in sulfuric acid using an oxidizing agent, and the graphene oxide obtained after purification and exfoliation is preferred.

[0010] The dispersion medium for the graphene oxide dispersion of the present invention is not particularly limited, but from the viewpoint of film formation described later, examples include water, alcohols such as methanol and ethanol, ketones such as acetone and methyl ethyl ketone, N,N-dimethylformamide, and N-methylpyrrolidone, and a mixture thereof may also be used. Among these, water, N,N-dimethylformamide, and N-methylpyrrolidone are preferred, with water being the most preferred.

[0011] The concentration of the graphene oxide dispersion of the present invention is preferably 0.0001 to 10%. Within this range, graphene oxide can adhere well. From the viewpoint of productivity and performance, 0.0001 to 5% is preferred, 0.001 to 3% is more preferred, and 0.01 to 2% is most preferred. Furthermore, it is preferable that the dispersion be subjected to a dispersion treatment to improve its dispersibility. Examples of dispersion treatments include shearing treatment using a homogenizer or ultrasonic treatment.

[0012] The graphene oxide of the present invention preferably has 10 layers or less. The number of layers can be analyzed using an electron microscope or the like. From the viewpoint of more effective adhesion, the number of layers of graphene oxide is preferably 1 to 10, more preferably 1 to 7, even more preferably 1 to 5, and most preferably 1 to 3. Furthermore, from the viewpoint of compatibility with both copper and the negative electrode material, and dispersibility, the carbon-oxygen ratio (O / C) in the graphene oxide is preferably in the range of 0.05 to 2, more preferably 0.1 to 1.5, even more preferably 0.2 to 1.2, and most preferably 0.4 to 1.0. By appropriately adjusting these O / C values, it is possible to prepare an optimal graphene oxide (film) depending on the copper current collector and negative electrode material being combined. In particular, from the viewpoint of tightly adhering the copper current collector and the organic binder, a higher O / C is better. Generally, graphene other than graphene oxide has an O / C value of 0.1 or less, is highly hydrophobic, and has little effect from the viewpoint of adhesion. The O / C ratio can be increased by increasing the amount of oxidizing agent or strengthening the oxidation conditions during graphene oxide synthesis, and can be decreased by reducing the graphene oxide.

[0013] [Graphene oxide coated copper current collector and method for manufacturing the same] The graphene oxide-coated copper current collector of the present invention has a graphene oxide film formed on a copper current collector, which is formed by bringing the copper current collector into contact with the graphene oxide dispersion. Graphene oxide spontaneously forms on the copper current collector, taking advantage of its shape and abundant oxygen functional groups.

[0014] The contact process and method of the present invention include spin coating, coating with a coater or applicator, impregnating a copper current collector (e.g., in the shape of copper foil) with a graphene oxide dispersion, and spraying the copper current collector. Among these, the impregnation method and the spraying method are more preferred. The concentration of the graphene oxide dispersion in the contact process is the same as the concentration of the graphene oxide dispersion described above. Even at low concentrations, graphene oxide spontaneously adsorbs onto the copper current collector, so it can be applied to a wide range of concentrations. The contact time is not particularly limited as long as time is ensured for the graphene oxide to spontaneously adsorb, but it is approximately 1 second to 24 hours. From a manufacturing process viewpoint, the contact time is preferably 1 second to 1 hour, more preferably 10 seconds to 30 minutes, and most preferably 1 minute to 10 minutes. Furthermore, it is preferable to contact the copper foil while moving it (for example, moving the copper foil in the graphene oxide dispersion in a direction parallel to the liquid surface) rather than statically contacting it. Since graphene oxide is in sheet form, it is preferable that the graphene oxide dispersion flows parallel to the copper foil. The speed at which the copper foil moves through the graphene oxide dispersion is preferably 1 cm / second or more. The temperature at contact is not particularly limited, but from a process viewpoint, 0 to 100°C is preferred, and 15 to 50°C is more preferred.

[0015] The graphene oxide-coated copper current collector of the present invention preferably has a removal step after the above contact step to remove excess graphene oxide by solvent washing. Examples of removal methods include spraying and washing with a solvent, or impregnation and washing in a solvent. The solvent used in the removal step is a graphene oxide dispersion and is equivalent to the preferred solvent.

[0016] The graphene oxide-coated copper current collector of the present invention may undergo a drying step between the contact step and the removal step. However, from the viewpoint of not leaving excess graphene oxide and not requiring extra processes, it is preferable that a drying step is not performed between the contact step and the removal step. However, drying after the removal step is preferable.

[0017] The graphene oxide-coated copper current collector of the present invention preferably has a graphene oxide film with 10 layers or less. The number of layers can be analyzed by an electron microscope or the like. From the viewpoint of more effectively interacting, the number of layers of graphene oxide is preferably 1 to 10 layers, more preferably 1 to 7 layers, still more preferably 1 to 5 layers, and most preferably 1 to 3 layers.

[0018] In the graphene oxide-coated copper current collector of the present invention, the graphene oxide film preferably has a carbon-oxygen element ratio (O / C) in the range of 0.05 to 2, more preferably 0.1 to 1.5, still more preferably 0.2 to 1.2, and most preferably 0.4 to 1.0. O / C can be appropriately adjusted according to the composition of the copper current collector and the negative electrode material used, and it is particularly preferable to adjust it according to the polarity of the negative electrode material. O / C can be adjusted by reduction after the formation of graphene oxide. The higher the degree of reduction (the smaller O / C), the higher the hydrophobicity. Examples of the reduction method include heat reduction and reduction using a reducing agent, but heat reduction is preferable because of the simplicity of the process. The heating atmosphere can be atmospheric, evacuated, or an inert atmosphere (such as a nitrogen atmosphere). From the viewpoint of allowing reduction to proceed well, an inert atmosphere is preferable. The reduction temperature is preferably 100°C or higher, and more preferably 150°C or higher. Since the higher the heating temperature, the more the reduction proceeds, the upper limit temperature is not particularly limited, but from the viewpoint of the process, it is preferably 1000°C or lower.

[0019] [Negative electrode active material] The negative electrode active material of the present invention preferably contains a silicon-containing substance. Examples of the negative electrode active material containing silicon (hereinafter sometimes referred to as a silicon-based negative electrode active material) include silicon (Si), an alloy containing silicon, a carbide containing silicon, a nitride containing silicon, an oxide containing silicon, and the like. Specifically, Si, SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu5Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, SiOx (0 < x ≤ 2), SnSiOx, LiSiO can be exemplified. It is preferably SiOx (0 < x ≤ 2), more preferably silicon monoxide (SiO) or the like. The cycle characteristics of the LIB can be improved. The negative electrode active material of the present invention may be one kind or two or more kinds may be used in combination. More preferably, it is two or more kinds.

[0020] The negative electrode active material of the present invention may contain other negative electrode active materials other than the silicon-based negative electrode active material. Examples of the other negative electrode active materials include carbon materials such as graphite, carbon black, fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril, polyacene-based conductive polymers, composite metal oxides such as lithium titanate, lithium alloys, and the like.

[0021] From the viewpoint of dispersibility, the content of silicon is preferably 5% by mass or more, more preferably 7% by mass or more, and still more preferably 10% by mass or more based on the total amount of the negative electrode active material. On the other hand, it is preferably 100% by mass or less, more preferably 90% by mass or less, and still more preferably 80% by mass or less.

[0022] [Composition for Lithium Ion Battery Negative Electrode] The composition for a lithium ion battery (LIB) negative electrode of the present invention only needs to contain the above negative electrode active material. The LIB anode composition of the present invention preferably contains 85% by mass or more of the anode active material relative to the total amount of the LIB anode composition, more preferably 90% by mass or more, and even more preferably 95% by mass or more. On the other hand, it is preferably 99% by mass or less, more preferably 98% by mass or less, and even more preferably 97% by mass or less.

[0023] The LIB anode composition of the present invention may contain other components. Examples of other components include conductive additives, solvents, dispersants, thickeners, film-forming aids, wetting agents, pH adjusters, stabilizers, polymerization inhibitors, surfactants, adhesion promoters, fillers, antioxidants, antistatic agents, dyes, and pigments.

[0024] As a conductive additive, conductive carbon is preferred because it tends to improve the output of LIBs. Examples of conductive carbon include carbon black, fibrous carbon, and graphite, but carbon black is more preferred. Specific examples of carbon black include Ketjenblack and acetylene black.

[0025] From the viewpoint of improving the output characteristics and electrical characteristics of the LIB, the content of the conductive additive is preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and even more preferably 1% by mass or more, relative to the total amount of the LIB anode composition. On the other hand, it is preferably 15% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0026] Examples of solvents include water; alcohols such as methanol, ethanol, isopyroxene, and hexanol; ketones such as acetone and 2-butanone; acetic acid esters such as methyl acetate, ethyl acetate, and butyl acetate; and ethers such as tetrahydrofuran, diethyl ether, 1,2-dimethylethane, and diethylene glycol dimethyl ether.

[0027] The solvent content is preferably 20% by mass or more, more preferably 25% by mass or more, and even more preferably 30% by mass or more, relative to the total amount of the LIB anode composition. On the other hand, it is preferably 70% by mass or less, more preferably 60% by mass or less, and even more preferably 50% by mass or less.

[0028] The pH of the LIB negative electrode composition of the present invention at 25°C is preferably 5 or higher, more preferably 5.5 or higher, even more preferably 6 or higher, and still more preferably 6.5 or higher, from the viewpoint of suppressing corrosion of the current collector. Furthermore, the pH of the LIB negative electrode composition at 25°C is preferably 10 or lower, more preferably 9 or lower, even more preferably 8 or lower, and still more preferably 7.5 or lower, from the viewpoint of suppressing corrosion of the current collector.

[0029] [Lithium-ion battery negative electrode] Electrodes for lithium-ion batteries (LIBs) include a positive electrode and a negative electrode. The electrodes of the LIB according to this embodiment can be used for either electrode, but are preferably used as a negative electrode. The negative electrode for the LIB has a negative electrode composite layer formed from an LIB negative electrode composition on a negative electrode current collector.

[0030] Examples of metals that can be used for the negative electrode current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. Of these, copper is preferred. The shape and dimensions of the negative electrode current collector are not particularly limited.

[0031] [Manufacturing method for lithium-ion battery negative electrodes] In this embodiment, the electrodes of the LIB can be formed, for example, by coating the current collector with the LIB negative electrode composition, or by immersing the current collector in the LIB negative electrode composition and then drying it to form a negative electrode composite layer.

[0032] The drying temperature is preferably 40°C or higher, and more preferably 50°C or higher. On the other hand, it is preferably 150°C or lower, and more preferably 130°C or lower. The electrodes may be subjected to pressure treatment, for example, using a mold press or a roll press, if necessary.

[0033] [Lithium-ion battery] The lithium-ion battery (LIB) of the present invention includes a positive electrode and the negative electrode. More specifically, the LIB comprises a positive electrode and the negative electrode, a separator provided between the positive electrode and the negative electrode, and an electrolyte impregnated in the separator and housed together with the positive electrode and the negative electrode in an outer casing. As a separator, for example, a film made of a resin such as polyethylene, polyolefin resin such as polypropylene, or fluororesin can be used.

[0034] An electrolyte solution can be used in which a supporting electrolyte is dissolved in an organic solvent. A lithium salt is used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (FSO2)2NLi, (CF3SO2)2NLi, and (C2F5SO2)2NLi. Examples of the organic solvent include carbonates such as dimethyl carbonate, ethylene carbonate, diethyl carbonate, propylene carbonate, butylene carbonate, and methyl ethyl carbonate; esters such as γ-butyrolactone and methyl formate; and ethers such as 1,2-dimethoxyethane and tetrahydrofuran.

[0035] The LIB according to this embodiment can be easily manufactured, for example, by stacking a positive electrode and a negative electrode with a separator in between, placing the resulting laminate in a battery container, and then injecting an electrolyte into the battery container and sealing it.

[0036] The battery container may contain, if necessary, expanded metal, fuses, overcurrent protection elements such as PTC elements, lead plates, etc., to prevent pressure buildup inside the battery and overcharging / discharging. Examples of battery shapes include coin-type, button-type, sheet-type, cylindrical, rectangular, and flat-type batteries, but the present invention is not limited to these examples. [Examples]

[0037] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0038] [Raman spectroscopy measurement] Raman spectroscopy was performed using the following equipment and conditions. Graphene oxide was present at 1600 cm⁻¹. -1 The determination was made based on the presence or absence of a peak called the G-band in the vicinity. Measurement device: Micro-Raman (JASCO NRS-3100) Measurement conditions: 532nm laser used, 20x objective lens, CCD acquisition time 1 second, 32 integrations (resolution = 4cm) -1 ) Measurement method: The presence of the characteristic G and D bands of graphene oxide is confirmed by checking for their presence or absence.

[0039] [X-ray photoelectron spectroscopy (XPS) measurement] XPS analysis was performed using the following equipment and conditions, and the O / C ratio was calculated. Shimadzu Kratos Co., Ltd. AXIS-NOVAX ray source, output AlKα-100W, pass energy 40eV, neutralization gun ON.

[0040] [Volume-average particle diameter] The polymer particles were diluted with deionized water, and their volume-average particle size (nm) of the binder emulsion was determined by dynamic light scattering using a light scattering particle size distribution analyzer (Spectris "Zetasizer Ultra").

[0041] [Example of graphene oxide preparation] A graphene oxide dispersion was synthesized using the following procedure. 15 g of graphite (Z-25, manufactured by Ito Graphite Co., Ltd.) and 640 g of sulfuric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were placed in a reaction vessel. 45 g of potassium permanganate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was added while adjusting the temperature to 30°C. After addition, the mixture was heated to 35°C for 30 minutes and reacted for 2 hours. After the reaction, 1070 ml of water and 42 ml of 30% hydrogen peroxide solution (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) were added to the reaction solution to stop the reaction. The resulting reaction solution was purified by repeated removal of the supernatant and redispersion with ion-exchanged water after standing sedimentation. After purification, the mixture was homogenized to prepare graphene oxide dispersion (1) (0.01% aqueous dispersion). Electron microscopy revealed that the obtained graphene oxide was a monolayer. The O / C ratio determined by XPS analysis was 0.55.

[0042] [LIB evaluation] [Example 1] (1-1) Fabrication of graphene oxide coated copper current collector Copper foil (manufactured by Fukuda Metal Foil & Powder Industry Co., Ltd., 16 μm thick) was impregnated in the graphene oxide dispersion (1) for 1 minute, and then thoroughly washed with deionized water without drying to remove excess graphene oxide. Afterward, it was dried in a 50°C forced-air dryer to produce a graphene oxide-coated copper current collector (1). Raman analysis confirmed the presence of graphene oxide on the copper current collector by the confirmation of the G band. The O / C ratio determined by XPS analysis was 0.55, similar to that of the original graphene oxide.

[0043] (1-2) Preparation of electrode slurry Carboxymethylcellulose (manufactured by Daicel Finechem, product name "CMC Daicel 2200", hereinafter referred to as "CMC") is added to deionized water, and stirred at 2000 rpm for 10 minutes using a stirring and defoaming machine (manufactured by Thinky, Awatori Rentaro ARE-310). A 2% by mass aqueous CMC solution was prepared by mixing. Fifty parts of the CMC aqueous solution obtained above were mixed with 80 parts by mass of negative electrode active material (1) (manufactured by Showa Denko Materials, graphite active material, "MAGE"), 20 parts by mass of negative electrode active material (2) (manufactured by Shin-Etsu Chemical Co., Ltd., silicon active material, "KSC-1265"), 2 parts of conductive additive (1) (manufactured by Showa Denko, "VGCF-H"), 3 parts of conductive additive (2) (manufactured by Denka, "Denka Black Powder"), and a predetermined amount of deionized water. The mixture was then stirred and mixed at 2000 rpm for 27 minutes using a stirring and defoaming machine. Subsequently, 6.18 parts by mass of SBR emulsion (solid content 48.5%, particle size 195 nm, aqueous dispersion) and a predetermined amount of deionized water were added as a binder and mixed to prepare the electrode slurry (negative electrode composition). At that time, the amount of deionized water added was adjusted so that the viscosity of the electrode slurry was 1350 ± 150 mPa·s.

[0044] (1-3) Fabrication of a negative electrode for battery evaluation The electrode slurry obtained above was applied to the graphene oxide-coated copper current collector obtained above, with a coating weight of 5.82 g / cm³ after drying. 2 The mixture was applied using an applicator, hot-air dried at 60°C for 10 minutes, and then vacuum-dried at 80°C for 10 hours. After that, it was pressed using a roll press to achieve a density of 1.5 g / cm³. 3 The negative electrode was obtained by pressure molding until it reached this state.

[0045] (1-4) Making a battery A lithium foil (manufactured by Honjo Metal Co., Ltd., 0.5 mm thick) was used as the positive electrode, the negative electrode obtained above, and a polyethylene separator (25 μm thick) were punched out into circular shapes (negative electrode Φ12 mm, lithium foil Φ15 mm, separator Φ16 mm). Using components for a CR2032 coin-type battery (manufactured by Hosen Co., Ltd.: case (made of SUS316L), cap (made of SUS316L), spacer (0.5 mm thick, made of SUS316L), wave washer (made of SUS316L), gasket (made of polypropylene)), coin-type LIBs were fabricated using the following procedure. First, the cap with the gasket attached, the lithium foil, and the separator were stacked in that order. Next, an electrolyte prepared by dissolving LiPF6 (manufactured by Stella Chemifa) at a concentration of 1.0 mol / L in a solution of ethylene carbonate (manufactured by Kishida Chemical Co., Ltd.):dimethyl carbonate (manufactured by Kishida Chemical Co., Ltd.):fluoroethylene carbonate (manufactured by Kishida Chemical Co., Ltd.) = 2:7:1 (volume ratio) was impregnated into the separator. Then, the negative electrode obtained above was placed so that the negative electrode coated surface faced the lithium foil, and a spacer, wave washer, and case were stacked on top in that order, and the assembly was sealed with a crimping machine (manufactured by Hosen Co., Ltd.) to produce a coin-type LIB.

[0046] (1-5) Charge / Discharge Test The coin-type LIB (design capacity 3.73mAh) obtained above underwent charge-discharge testing using a charge-discharge test apparatus (manufactured by Asuka Electronics Co., Ltd.) at a temperature of 25°C. The test involved discharging at 0.1C with constant current and constant voltage down to 0.01V, then charging at 0.1C, 0.1C, 0.2C, 1C, 2C, 0.1C, and 0.1C in that order to 1.5V with constant current, then discharging at 0.5C with constant current and constant voltage down to 0.01V, and finally charging at 0.5C with constant current to 1.5V. This process was repeated 23 times, for a total of 30 charge-discharge cycles. The cycle characteristic (%) was calculated as: discharge capacity at cycle 30 / discharge capacity at cycle 10 × 100.

[0047] [Example 2] The evaluation was performed using the same procedure as in Example 1, except that 26.08 parts by mass of acrylic emulsion (solids content 11.5%, particle size 285 nm, aqueous dispersion) was used as a binder instead of the SBR emulsion.

[0048] [Example 3] Similar to Example 1, a graphene oxide-coated copper current collector (1) was prepared, and then the graphene oxide-coated copper current collector (1) was heat-treated at 200°C in air for 2 hours to prepare a graphene oxide-coated copper current collector (2) (O / C=0.15), which was evaluated using the same procedure as in Example 1.

[0049] [Comparative Example 1] The evaluation was carried out using the same procedure as in Example 1, except that untreated copper foil was used as the copper current collector instead of the graphene oxide-coated copper current collector obtained in Example 1.

[0050] [Comparative Example 2] The evaluation procedure was the same as in Comparative Example 1, except that 26.08 parts by mass of acrylic emulsion (11.5% solids content, 285 nm particle size aqueous dispersion) was used as a binder instead of the SBR emulsion.

[0051] Table 1 shows the results of LIB evaluation using the copper current collectors obtained in Examples 1-3 and Comparative Examples 1-2. From the results in Table 1, it was clear that the graphene oxide-coated copper current collector of this disclosure exhibits high cycle characteristics. Furthermore, it was found that those coated with unreduced graphene oxide exhibit even higher cycle characteristics than those coated with reduced graphene oxide.

[0052] [Table 1]

[0053] By using the graphene oxide-coated copper current collector of the present invention, it is possible to provide a lithium-ion battery (LIB) with excellent cycle characteristics.

Claims

1. A graphene oxide coated copper current collector for lithium-ion batteries, characterized in that the surface of the copper current collector is coated with graphene oxide, wherein the O / C ratio determined by XPS analysis of the graphene oxide is 0.4 or higher.

2. The graphene oxide coated copper current collector according to claim 1, characterized in that the copper current collector is a copper current collector for a silicon negative electrode.

3. A method for manufacturing a graphene oxide-coated copper current collector according to claim 1 or 2, characterized by the steps of bringing copper foil into contact with a dispersion of graphene oxide, and removing excess graphene oxide by washing without drying after the contact step.

4. A lithium-ion battery having a graphene oxide-coated copper current collector according to claim 1 or 2.

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