TW202034563A - Copper foil and lithium ion battery negative electrode current collector including said copper foil, and manufacturing method thereof - Google Patents

Abstract

The purpose of the present invention is to provide: a novel copper foil and a lithium ion battery negative electrode current collector including said copper foil; and a manufacturing method thereof. According to one embodiment, produced is a copper foil having a 5 nm-tall protruding part on at least a portion of a surface thereof, where the density of the protruding part is 15 to 100 per 3.8 [mu]m. Also, a negative electrode current collector is produced using this copper foil.

Description

Copper foil, negative electrode current collector of lithium ion battery containing the copper foil, and manufacturing method of the negative electrode current collector

The present invention relates to a copper foil, a negative electrode current collector of a lithium ion battery containing the copper foil, and a method for manufacturing the negative electrode current collector.

In the negative electrode current collector of a lithium ion battery (LIB), if a large-capacity active material is used for high output and high energy density, the volume expansion rate of the active material during charging and discharging increases. Therefore, after repeated charging and discharging, the adhesive material that binds the active material and the current collector will be broken, and the adhesive material will be peeled off from the interface of the active material and the current collector, which degrades the cycle characteristics. In order to prevent deterioration, an invention that increases the amount of adhesive material on the copper foil side to improve the adhesion between the copper foil and the negative electrode compound layer has been disclosed (Japanese Patent Laid-Open No. 10-284059). In addition, another invention discloses an invention in which whisker-like copper oxide is formed on the surface of a copper foil plate to increase the surface area to improve the adhesion between the copper foil and the active material (Japanese Patent Laid-Open No. 11-307102).

The object of the present invention is to provide a novel copper foil, a negative electrode current collector of a lithium ion battery containing the copper foil, and a method for manufacturing the negative electrode current collector.

The copper foil of one embodiment of the present invention has protrusions with a height of 5 nm or more on at least a part of the surface, and the density of the protrusions in this part is 15 or more and 100 or less per 3.8 μm on average. The surface can be plated. In this part, the density of the convex portions may be 20 or more and 62 or less on average per 3.8 μm. In addition, the three-point standard deviation σ of the surface roughness Rz of the part may be 0.5 or less, or 0.3 or less. In addition, the surface roughness Rz of this part may be 2 μm or less on average, or may be 1.54 μm or less. The calculated number of currents to be binarized per 4μm ² can be an average of 200 or more or 500 or more. The total current area per 4μm ² can be an average of 100000nm ² or more or 300,000nm ² or more. When measured by X-ray photoelectron spectroscopy, the amount of oxygen at 5nm from the surface to the depth direction can be 50% or less or 25% or less. At least a part of the surface may be formed with a metal layer other than copper. The thickness of the metal layer may be 15 nm or more and 200 nm or less.

Another embodiment of the present invention is a negative electrode current collector of a lithium ion battery, which includes any of the above-mentioned copper foils.

Another embodiment of the present invention is a method for manufacturing a negative electrode current collector of a lithium ion battery. The negative electrode current collector of the lithium ion battery includes any of the above-mentioned copper foils. The manufacturing method includes: a method selected from sodium chlorite and sodium hypochlorite The first step of oxidizing the copper surface of copper foil with more than one of potassium chlorate and potassium perchlorate to form protrusions; the second step of plating the oxidized copper surface; and using the copper surface plating treatment Then the copper foil is the third step of manufacturing the negative electrode current collector. Before the second step, it may further include a step of dissolving the copper surface oxidized in the first step and/or a fourth step of reducing.

In addition, in this specification, the average value is measured at a random number of points, for example, the average of the three-point measurement.

Effect of the present invention: According to the present invention, it is possible to provide a novel copper foil, a negative electrode collector of a lithium ion battery containing the copper foil, and a method for manufacturing the negative electrode collector.

The following examples illustrate the embodiments of the present invention in detail. In addition, the purpose, features, advantages and concept of the present invention can be understood by those with ordinary knowledge in the technical field of the invention from the description of this specification, and those with ordinary knowledge in the technical field of the invention can easily be understood from the description of this specification. Reproduce the invention. The embodiments and specific examples of the invention described below represent preferred embodiments of the present invention for illustration and description, and the present invention is not limited to these aspects. Those with ordinary knowledge in the technical field to which the invention pertains will understand that various modifications can be made based on the description of this specification within the intent and scope of the invention disclosed in this specification.

<Copper foil> The copper foil disclosed in this specification may be rolled copper foil, electrolytic copper foil or copper alloy foil. The higher the copper content or purity, the better, preferably more than 50%, more preferably more than 60%, more preferably more than 70%, more preferably more than 80%, more preferably more than 90%, and more preferably It is 95% or more, more preferably 98% or more, and still more preferably 99.5% or more. The thickness of the copper foil is not particularly limited, and it is preferably a thickness used as a negative electrode current collector of a lithium ion battery, for example, 5 μm to 100 μm, and the thickness of the copper foil can be selected from this range according to the application. In addition, the surface roughness of the copper foil is not particularly limited, and copper foil of any thickness can be used. However, if the surface roughness is too large, the tensile strength decreases, and the negative electrode material cannot be filled to the bottom of the unevenness, which reduces the adhesion. In addition, when the surface roughness is large and there are few convex parts, current will be concentrated on the convex parts, and active material peeling may occur and the battery characteristics will deteriorate. Therefore, the surface roughness is preferably 2 μm or less.

This copper foil has convex parts with a height of 5nm or more on at least a part of the surface in the image taken by the scanning electron microscope. The density of the convex parts is measured in a direction parallel to the surface, preferably an average of 15 per 3.8μm More than one and 100 or less, more preferably 20 or more and 62 or less on average. The number of convex parts is calculated as convex parts when the length of the line segment connecting the minimum points of the concave parts at both ends of the convex part is more than 5nm in the image taken by the scanning electron microscope. The height of the convex portion is calculated using a scanning electron microscope, especially a conjugate focus scanning electron microscope, based on Rz specified in JIS B 0601:2001.

The three-point standard deviation σ of the surface roughness Rz of a part of the surface having a convex portion with a height of 5 nm or more is preferably 0.5 or less, more preferably 0.3 or less. The smaller the three-point standard deviation σ of Rz, the more average the unevenness. In addition, the average Rz is preferably 2 μm or less, more preferably 1.54 μm or less. The smaller the average Rz, the smaller the unevenness.

These properties are a better structure when copper foil is used as a negative electrode current collector. The principle is not particularly limited. When the number of protrusions is small, the surface area of the copper foil is reduced, so the adhesion of the copper foil to the negative electrode is deteriorated, and as a result, the maintained capacitance is reduced. When the number of convex parts is small, Rz needs to be increased in order to increase the surface area. When Rz is increased, current is concentrated on the convex parts, so the copper foil and the active material are easily peeled off, reducing the capacity retention rate. In addition, when the three-point standard deviation of the surface roughness Rz, that is, the deviation is large, current concentration is likely to occur when used in a negative electrode current collector, and as a result, the capacity retention rate is reduced.

For example, the larger the number of current dispersion of the negative electrode current collector system, the more the current concentration can be suppressed, and the separation of the negative electrode material is less likely to occur. Therefore, the high-speed charge and discharge characteristics (C-rate) have excellent capacitance retention. The average number of current dispersions per 4 μm ² copper foil is preferably 200 or more, more preferably 400 or more, and still more preferably 500 or more. That is, the density of the current dispersion number is preferably 50 pieces/μm ² or more, more preferably 100 pieces/μm ² or more, and still more preferably 125 pieces/μm ² or more. In addition, the larger the area through which the current flows when the specific current amount or more is used as the threshold value, the easier the electricity flows, and the power collection is excellent. The average total area per 4 μm ^{2 of} copper foil is preferably 100,000 nm ² or more, more preferably 200,000 nm ² or more, and still more preferably 300,000 nm ² or more. That is, the ratio of the area through which the current flows when the specific current amount or more is used as the threshold value is preferably 2.5% or more, more preferably 5.0% or more, and still more preferably 7.5 or more. The specific current amount is preferably -1 nA or more, more preferably -30 nA or more, and still more preferably -60 nA or more. In addition, these values can be measured using conventional methods, such as the methods described in the examples.

If the amount of oxygen contained in the negative electrode material is large, the resistance increases, making it difficult for current to flow. Therefore, in order to make the area through which the current flows is 10000nm ² or more, the lower the amount of oxygen contained in the negative electrode material, the better. Specifically, the amount of oxygen at a depth of 5nm is preferably 50% or less, and more preferably 40% or less. It is more preferably 35% or less, and more preferably 25% or less. In addition, this amount of oxygen can be measured by X-ray photoelectron spectroscopy (XPS).

In addition, by forming a metal layer other than copper on the surface, current dispersibility can be improved, current can flow easily, and surface oxidation can be prevented, so the contact angle with water is unlikely to change over a long period of time. Therefore, it is preferable to form a metal layer on the surface. For metals other than copper, tin, silver, zinc, aluminum, titanium, bismuth, chromium, iron, cobalt, nickel, palladium, gold, platinum, or various alloys can be used. The metal layer is formed by, for example, plating. The thickness of the metal layer is preferably 15 nm or more and 200 nm or less, more preferably 30 nm or more and 200 nm or less. If it is less than 15nm, it is likely to change over a long period of time, and if it exceeds 200nm, the unevenness will be filled by leveling, so the amount of current dispersion is reduced and current concentration is likely to occur.

<The manufacturing method of copper foil and negative electrode current collector of lithium ion battery> The manufacturing method of copper foil disclosed in this specification includes the first step of oxidizing the copper surface of the copper foil to form fine protrusions, and further adjusting the oxidized copper foil The second step of the protrusions formed on the surface, the third step of using the copper foil with the adjusted protrusions on the copper surface to manufacture the negative electrode current collector of the lithium ion battery. In addition, the second step includes at least one step of subjecting the oxidized copper surface to plating treatment, reduction treatment or dissolution treatment. The steps are described in detail below.

(1) First step (oxidation step): In the first step, the copper surface of the copper foil is first oxidized with an oxidizing agent to form a layer containing copper oxide, and to form protrusions on the surface. The oxidizing agent is not particularly limited. For example, aqueous solutions or buffers such as sodium chlorite, sodium hypochlorite, potassium chlorate, potassium perchlorate, potassium persulfate, etc. can be used, and aqueous solutions containing sodium chlorite or sodium hypochlorite are preferably used. Use these to form a better surface shape. Various additives (such as phosphate such as trisodium phosphate dodecahydrate or surface active molecules) can be added to the oxidizing agent. Surface-active molecules include, for example, porphyrin, porphyrin macrocycles, expanded porphyrin, condensed porphyrin, porphyrin linear polymer, porphyrin-sandwich coordination complex, porphyrin array, silane, tetraorgano-silane , Aminoethyl-aminopropyl-trimethoxysilane, (3-aminopropyl)trimethoxysilane, (1-[3-(trimethoxysilyl)propyl]urea) (l- [3-(Trimethoxysilyl) propyl]urea), (3-aminopropyl)triethoxysilane, (3-epoxypropyloxypropyl)trimethoxysilane, (3-chloropropyl)trimethoxy Silane, (3-epoxypropyloxypropyl)trimethoxysilane, dimethyldichlorosilane, 3-(trimethoxysilyl)propyl methacrylate, ethyltriethoxysilane , Triethoxy (isobutyl) silane, triethoxy (octyl) silane, ginseng (2-methoxyethoxy) (vinyl) silane, chlorotrimethylsilane, methyltrichlorosilane , Silicon tetrachloride, tetraethoxysilane, phenyltrimethoxysilane, chlorotriethoxysilane, vinyl-trimethoxysilane, amine, sugar, etc. Furthermore, in addition to the oxidizing agent, alkaline compounds such as sodium hydroxide and potassium hydroxide may be contained.

The additive used in this oxidation step is preferably an additive that moderately inhibits the formation of surface protrusions caused by oxidation, such as a silane coupling agent containing a silicon compound, whereby the surface unevenness becomes finer and the height of the protrusions becomes More uniform. By using a copper foil with a uniform height of the surface protrusions to manufacture the negative electrode current collector of the lithium ion battery, the partial unevenness of the coating amount of the negative electrode material to the unevenness can be reduced. In this way, there is no unevenness in the flow of current, and the battery characteristics are also improved. And productivity is also improved.

The oxidation reaction conditions are not particularly limited, and the liquid temperature of the oxidizing agent is preferably 40 to 95°C, more preferably 45 to 80°C. The reaction time is preferably 0.5 to 30 minutes, more preferably 1 to 10 minutes.

In addition, before this oxidation step, degreasing by alkali treatment or cleaning by acid treatment may be performed as pretreatment. The specific method of alkali treatment or acid treatment is not particularly limited. For alkali treatment, for example, 30-50g/L alkaline aqueous solution is preferably used, more preferably 40g/L alkaline aqueous solution, for example, sodium hydroxide aqueous solution can be used at 30-50°C. After processing for about 0.5 to 2 minutes, wash with water. In addition, the acid treatment can be carried out by immersing the copper surface in sulfuric acid at a liquid temperature of 20 to 50°C and 5 to 20% by weight for 1 to 5 minutes and then washing with water. After acid treatment, a weak alkali treatment can be further carried out to reduce uneven treatment and prevent mixing of acid and oxidant used for cleaning treatment. The alkali treatment is not particularly limited, preferably 0.1-10g/L alkaline aqueous solution, more preferably 1-2g/L alkaline aqueous solution, alkaline aqueous solution, for example, sodium hydroxide aqueous solution, treated at 30-50℃ It takes 0.5 to 2 minutes. In addition, the copper surface can be physically roughened by etching, etc., but the shape of the convex portion formed on the copper surface at this time is generally related to the crystallinity of the copper to be processed, so only physical The roughening treatment does not form fine unevenness. In order to obtain a copper foil with fine unevenness, an actual oxidation step is required.

(2) Second step: The second step includes at least one of (2-1) a plating treatment step, (2-2) a reduction treatment step, and (2-3) a dissolution treatment step. The plating treatment step may be performed after the reduction treatment step, or may be performed after the dissolution treatment. Through the oxidation treatment in the first step, the copper surface is roughened to have fine protrusions. Through the second step of the present invention, the protrusions formed on the copper surface are further adjusted. Each processing system of the second step is described below.

(2-1) Plating treatment step: In this step, the oxidized copper surface is plated with a metal other than copper to adjust the protrusions on the oxidized copper surface. Conventional techniques can be used for the plating treatment. For metals other than copper, tin, silver, zinc, aluminum, titanium, bismuth, chromium, iron, cobalt, nickel, palladium, gold, platinum or various alloys can be used. The plating method is also not particularly limited, and plating can be performed by electrolytic plating, electroless plating, vacuum evaporation, chemical conversion treatment, or the like. Preferably, electrolytic plating is used. Compared with electroless plating, it can be easily reduced to metallic copper and has excellent power collection.

In the case of electroless nickel plating, it is preferable to use a catalyst for treatment. The catalyst can use iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and these salts. The reducing agent used in the case of electroless nickel plating is preferably a reducing agent with no catalytic activity of copper or copper oxide. Examples of reducing agents in which copper or copper oxide does not have catalytic activity include hypophosphites such as sodium hypophosphite.

In this way, a metal layer maintaining the fine unevenness formed in the first step is obtained, whereby the surface is protected, and the long-term stability of the composite copper foil is improved. The thickness of the plating is not particularly limited, but if it is too thick, the number of protrusions will be reduced due to the leveling effect, resulting in a reduction in RSm, a reduction in surface area, and a reduction in power collection, resulting in deterioration of battery characteristics, so it is preferably 1 μm or less.

In the plating treatment step, unless the purity of copper is improved, it is difficult to uniformly form plating, and pure copper is preferably used. Therefore, generally, the oxide film on the surface is removed and the plating process is performed. In the method disclosed in the present invention, an oxide film is used to form a better shape, and then a plating process is performed to obtain the adhesion and battery characteristics required for the production of the current collector of the lithium ion battery.

(2-2) Reduction treatment step: In this step, a chemical solution containing a reducing agent (reduction chemical solution) is used to reduce the copper oxide formed on the copper foil to adjust the number or length of the bumps. The reducing agent can be DMAB (dimethylaminoborane), diborane, sodium borohydride, hydrazine, etc. In addition, the reduction chemical liquid is a liquid containing a reducing agent, an alkaline compound (sodium hydroxide, potassium hydroxide, etc.), and a solvent (pure water, etc.).

(2-3) Dissolution treatment step: In this step, dissolve the oxidized copper surface with a solvent to adjust the convexity of the oxidized copper surface. The dissolving agent used in this step is not particularly limited, and examples thereof include chelating agents and biodegradable chelating agents. Specifically, there are EDTA (ethylenediaminetetraacetic acid), DHEG (dihydroxyethylglycine), GLDA (tetrasodium L-glutamic acid diacetate), EDDS (ethylenediamine-N,N'-di Succinic acid), HIDS (sodium 3-hydroxy-2,2'-imino disuccinate), MGDA (trisodium methylglycine diacetate), ASDA (tetrasodium aspartate diacetate), HIDA (N-2-Hydroxyethyliminodiacetic acid disodium salt), sodium gluconate, hydroxyethylidene diphosphonic acid, etc.

The pH value of the dissolving agent is not particularly limited, but due to its high solubility in acidity, it is difficult to control the treatment and easy to produce uneven treatment. Therefore, it is preferably alkaline, more preferably pH 9.0 to 14.0, and preferably pH 9. 0 to 10.5, and more preferably pH 9.8 to 10.2.

In this step, the dissolution rate of copper oxide is 35-99%, preferably 50-99%, and the copper surface is treated until the thickness of the copper oxide is 4-300 nm, preferably 8-200 nm. In addition, the thickness of the copper oxide can be measured by the continuous electrochemical reduction method (SERA). Under this condition, the number and length of the surface bumps are better to reduce uneven processing. Therefore, it is better to conduct a pilot test first and set conditions such as temperature and time to obtain such a copper oxide layer. In addition, the dissolution rate refers to the ratio of the copper oxide on the copper surface that is dissolved and removed from the copper surface.

By performing the second step on the copper foil in this way, a composite copper foil with adjusted surface protrusions can be manufactured, which is suitable for the negative electrode current collector of a lithium ion battery.

The copper foil manufactured in the second step can be subjected to coupling treatment using silane coupling agent, chromate coating treatment, and anti-rust treatment using benzotriazoles.

(3) The third step (the manufacturing step of the negative electrode current collector): the copper foil processed as above can be used to manufacture the negative electrode current collector of the lithium ion battery and the negative electrode according to the conventional method. For example, a negative electrode material containing a carbon-based active material is prepared and dispersed in a solvent or water to form an active material slurry. After coating this active material slurry on copper foil, the solvent or water is evaporated and dried. After pressing and drying again, the negative electrode current collector is formed into a desired shape. In addition, the negative electrode material may also include silicon or silicon compound, germanium, tin, or lead, which has a larger theoretical capacity than the carbon-based active material. Moreover, in addition to the organic electrolyte solution in which lithium salt is dissolved in an organic solvent, the electrolyte system may also use a polymer formed of polyethylene glycol or polyvinylidene fluoride. In addition to lithium ion batteries, it can also be applied to lithium ion polymer batteries.

Examples: [Evaluation of roughening treatment of copper foil and copper foil surface] The following copper foils were used as examples and comparative examples, and the treatment described was performed.

In Examples 1 to 3, the matte surface treatment layer of a commercially available copper foil (B-Foil manufactured by Targray) was removed, and various surface treatments were applied. In Examples 4 to 7, the surface treatment layer of a commercially available copper foil (NC-WS manufactured by Furukawa Electric Co., Ltd.) was removed, and the surface treatment described later was applied. Comparative Example 1 used a matte surface of a commercially available copper foil (B-Foil manufactured by Targray), Comparative Example 2 used a commercially available copper foil (NC-WS manufactured by Furukawa Electric Co., Ltd.), and Comparative Example 3 used a commercially available copper foil (Targray B-Foil) bright surface (anode contact surface).

In addition, the processing conditions of the first step and the second step are organized in the table of FIG. 1. The pretreatment conditions and the coating conditions of the negative electrode material in the examples and comparative examples are the same.

(1) Pretreatment: [Alkaline degreasing treatment] After immersing the copper foil in a 40g/L sodium hydroxide aqueous solution at a liquid temperature of 50°C for 1 minute, it is washed with water.

[Pickling treatment] The copper foil subjected to alkali degreasing treatment was immersed in a 10% by weight sulfuric acid aqueous solution at a liquid temperature of 25°C for 2 minutes, and then washed with water.

[Pre-dip treatment] The pickled copper foil is immersed in a prepreg chemical solution with a liquid temperature of 40°C and 1.2 g/L of sodium hydroxide for 1 minute.

(2) The first step (oxidation treatment): First, the first step is to apply alkaline aqueous solution to the copper foils of Example 1, Example 2, Example 3, Example 4, Example 5 and Example 7 ( 20g/L sodium hydroxide, 60g/L sodium chlorite, 2g/L 3-epoxypropyloxypropyltrimethoxysilane) for oxidation treatment. The treatment temperature and treatment time were 45°C and 1 minute in Example 1, 73°C and 2 minutes in Examples 2, 3, 4, and 7, and 73°C and 3 minutes in Example 5.

The copper foil of Example 6 was subjected to oxidation treatment with an alkaline aqueous solution (20 g/L sodium hydroxide, 60 g/L sodium chlorite) at 73°C for 8 minutes. In addition, the copper foils of Comparative Examples 1 to 3 were not subjected to surface treatment such as oxidation treatment of the present invention.

(3) Second step: Next, the second step is to perform more than one (3-1) dissolution treatment, (3-2) plating treatment and (3-3) on the copper foil that has undergone the oxidation treatment in the first step. ) Reduction processing.

(3-1) Dissolution treatment: For the copper foils of Example 2, Example 3, and Example 7, after the oxidation treatment in (2), use the solvent L-glutamic acid tetrasodium diacetate (38g/L), Dissolve treatment at 55°C. The processing time is 1 minute in Example 2, 2 minutes in Example 3, and 3 minutes in Example 7.

(3-2) Plating treatment: For the copper foil of Example 1 and Example 4, after the oxidation treatment of (2), for the copper foil of Example 2 and Example 3, dissolve in (3-1) After the treatment, electrolytic plating was applied using an electrolyte for nickel plating (450g/L nickel sulfamate, 40g/L boric acid). The current density is 1Å/dm ² and the time is 15 seconds. The other copper foils were not plated.

(3-3) For the copper foils of Example 5 and Example 6, after the oxidation treatment of (2), use a solvent (5g/L dimethylaminoborane, 5g/L sodium hydroxide) at room temperature Leave for 3 minutes for reduction treatment.

(4) Measurement of the height and number of protrusions, and the surface roughness: For the copper foil processed by (1) to (3), observe the second figure (A) with a scanning electron microscope (SEM). (B) Photo. Use this captured image to determine the number of protrusions in the cross section. The number of convex parts is calculated as convex parts when the length of the line segment connecting the minimum points of the concave parts at both ends of the convex part is more than 5nm in the image taken by the scanning electron microscope. An example of the calculation method (calculation example 5) is shown in Figure 2 (C).

In addition, the surface roughness Rz was measured using a conjugate focus scanning electron microscope OPTELICS H1200 (manufactured by Lasertec Co., Ltd.), and calculated based on Rz specified in JIS B 0601:2001. The measurement condition setting system is that the scan width is 100μm, the scan type is Area, the light source is blue light, and the cut-off value is 1/5. Attach objective lens x100, eyepiece x14, digital zoom x1, and set the Z pitch to 10nm, obtain data at 3 positions, and calculate the standard deviation. Also, Rz is the average of 3 positions.

Table 1 Example Comparative example 1 2 3 4 5 6 7 1 2 3 Convex Number 56 20 41 62 58 49 36 2 4 7 Rz n=1(μm) 0.58 0.48 1.45 0.33 0.33 0.78 0.48 0.52 0.34 3.35 n=2(μm) 0.46 0.44 1.82 0.35 0.38 0.98 0.53 0.59 0.29 2.60 n=3(μm) 0.50 0.43 1.36 0.42 0.30 0.75 0.67 0.63 0.30 2.19 Average (μm) 0.51 0.45 1.54 0.36 0.33 0.84 0.56 0.58 0.31 2.71 Standard deviation 0.06 0.02 0.25 0.05 0.04 0.13 0.10 0.05 0.02 0.59

In this way, in any sample of the example, there are an average of 10 or more convex portions per 3.8 μm in height of 5 nm or more, the average Rz is 2.00 μm or less, and the standard deviation is 0.3 or less.

(5) Coating of negative electrode material: (5-1) Coating of water-based negative electrode material: This evaluation uses the copper foils of Example 1, Example 2, Example 3 and Comparative Example 1. Graphite (EQ-Lib-MCMB manufactured by MTI), acetylene black (Li-400 manufactured by Denka), CMC (carboxymethyl cellulose, CMC DAICEL 2200 manufactured by Daicel FineChem), SBR (styrene butadiene rubber, BM-400B manufactured by ZEON, Japan) ), silicon (manufactured by Tekna Advanced Materials) weighed into the specified ratio (graphite: 86.5 wt%, acetylene black: 1.5 wt%, CMC: 5.0 wt%, SBR: 2.5 wt%, silicon: 4.5 wt%), with pure water Adjust the viscosity.

After that, stir graphite, acetylene black, CMC, and silicon in a planetary stirring device until uniform, and finally add the SBR solution, and then stir. A bar coater (bar coater) was used to set the coating thickness to 150 μm to coat the copper foil. After coating, it was dried at 70°C for 2 hours to remove moisture, and pressed using roll pressing so that the thickness of the negative electrode material was 30 μm and the copper foil and the negative electrode material were closely adhered. After that, drying was performed in a vacuum decompression dryer at 70°C for 12 hours.

(5-2) Coating of solvent-based negative electrode material: This evaluation uses the copper foils of Example 4, Example 5, Example 6, Comparative Example 1, Comparative Example 2, and Comparative Example 3. Use graphite (made by Japanese black lead), acetylene black (Li-400 manufactured by Denka), PVDF (polyvinylidene fluoride, L#1120 manufactured by KUREHA), weighed to the specified ratio (graphite: 85% by weight, acetylene black: 5 Wt%, PVDF: 10 wt%). Use NMP as a solvent to adjust the viscosity.

After that, graphite, acetylene black, and PVDF are stirred until uniform in a planetary stirring device, and the coating thickness is set to 150 μm to be coated on the copper foil with a coating bar. After coating, it was dried at 80° C. for 2 hours to remove the solvent, and it was pressed using roll pressing so that the thickness of the negative electrode material was 30 μm and the copper foil and the negative electrode material were closely adhered. After that, it was dried in a vacuum decompression dryer at 120°C for 12 hours.

Figure 3 is a graph showing the coating stability of the solvent-based negative electrode material. The left of Figure 3 is the result of Example 4. The adhesion is good due to the large number of convexities, and the negative electrode agent is uniformly coated due to the capillary phenomenon. On the other hand, the right of Fig. 3 is the result of Comparative Example 1. Since there are few protrusions, adhesion and capillarity cannot be obtained, so partial peeling occurs in many places.

(6) Production of button batteries: the production of button batteries, the negative electrode is used (5) The samples made in the coating of negative electrode materials. Use 1M LiPF6/EC-DEC (1:1) as electrolyte, and use negative electrode, separator and lithium foil to make button battery.

(7) Measurement of charge and discharge characteristics: After the electrolyte is reduced and decomposed at 0.2C, 1 cycle, the thin film formed on the surface of the negative electrode, namely SEI (Solid Electrolyte Interphase), is discharged after CC-CV (voltage 10mV, (Current up to 0.1C) mode, charging system CC (up to voltage 1500mV) mode. After repeating 1C⇒3C⇒5C⇒1C at 30°C for 3 times, repeat 1C⇒3C⇒5C⇒1C at 50°C. Three cycles, the characteristics of the third cycle at 5C at 50°C were evaluated.

(8) Measurement of the residual rate of negative electrode material: Use the copper foil coated with negative electrode material in (5) to calculate the residual rate of negative electrode material as an evaluation of adhesion. First, the weight of the copper foil coated with the negative electrode material is measured. After that, stick double-sided tape on the board for fixing, stick scotch tape on it and make the adhesive surface of the scotch tape contact the negative electrode material, and then stick the negative electrode material surface of the copper foil coated with the negative electrode material After contacting the cellophane tape and applying a pressure of 5kN/inch ² , it was peeled with a peel strength tester (manufactured by Imada) under 90° peel strength test conditions (JIS 0237:2009) to measure the amount of negative electrode material remaining on the copper foil. The test method is shown in Figure 4.

The residual rate of negative electrode material was calculated using the following formula. Residual rate of negative electrode material [%] = (total weight after test-weight of copper foil) / (total weight before test-weight of copper foil) × 100

The evaluation results of the water-based negative electrode material are shown in Table 2. The evaluation results of the solvent-based negative electrode materials are shown in Table 3.

Table 2 Example 1 Example 2 Example 3 Example 4 Residual rate of anode material (%) 35% 32% 31% 28% Capacity maintenance rate (%) 70.8 68.9 70.6 65.9

Table 3 Example 4 Example 5 Example 6 Example 7 Comparative example 1 Comparative example 2 Comparative example 3 Residual rate of anode material (%) 25% 25% 26% 16% Peel off 11% 12% Capacity maintenance rate (%) 88.3 89.5 86.5 86.3 Peel off 82.3 85.4

In this way, a copper foil with protrusions with a height of 5 nm or more on at least a part of the surface and an average density of 15 or more and 100 or less protrusions per 3.8 μm is used to produce a negative electrode current collector for a lithium ion battery. This can improve the adhesion between the copper foil and the negative electrode and the capacity retention rate.

(9) Measurement of the amount and area of current dispersion: As an example, the sample copper foil was used in addition to the above examples 3 to 6, and the same conditions as in Example 1, except that the plating treatment time was extended, and the plating time was adjusted The amount of coulomb is such that copper foil with a plating thickness of 100nm (Example 8) and 200nm (Example 9) is used as a comparative example. In addition to the above-mentioned comparative examples 1 to 3, a commercially available copper foil (Furukawa Electric NC-WS manufactured by Industrial Co., Ltd.) only the same oxidation treatment (no plating treatment) as in Example 1 (Comparative Example 4) and the same conditions as in Example 1 were applied. Only the plating treatment time was shortened so that the plating thickness was 10nm (Comparative Example 5). In addition, the plating thickness here is the average thickness in the vertical direction of plating. In other words, the copper foil is dissolved in 12% nitric acid, and the solution is analyzed with an ICP emission spectrometer 5100 SVDV ICP-OES (manufactured by Agilent Technologies) to measure the concentration of the metal used for plating, considering the density of the metal and the surface area of the metal layer Calculate the average thickness of the metal layer when the layer is formed as the plating thickness.

Using an atomic force microscope (AFM) on these sample copper foils, the current image in Figure 5 was obtained under the following setting conditions. The current image obtained is adjusted to only display the current value below -60nA. In addition, in this measurement, in order to remove the influence of the oxidation of the copper foil surface on the current image, the bias voltage was set to a negative value. Therefore, the smaller the current value, the smaller the resistance and the easier current flow.

Device: Hitachi High-Tech Science system probe station AFM5000II Connected model: AFM5300E Cantilever: SI-DF3-R Use the automatic setting function of AFM5000II to set (Amplitude attenuation rate, scanning frequency, I gain, P gain, A gain, S gain) Scanning area: 2μm square Number of pixels: 512x512 Measurement mode: Current (nano) Measuring field of view: 2μm SIS mode: use Scanner: 20μm scanner Bias voltage: -0.5V Measuring atmosphere: vacuum

Use image processing software (WINROOF 2018 manufactured by Mitani Corporation) to convert the obtained current image into a black and white image and then perform binarization processing, and measure the number and total area of the current portion (green portion) per 4μm ² copper foil.

(10) Oxygen ratio at a depth of 5nm: X-ray photoelectron spectroscopy (XPS) is used to measure the oxygen ratio from the surface of the negative electrode body to a depth of 5nm. The measuring device used Quantera SXM (manufactured by ULVAC-PHI) and monochromatic AlKα (1486.6 eV) as excitation X-rays. Obtain a narrow spectrum for all elements detected by Survey Spectrum. In the depth direction, Ar sputtering was performed 12 times at 2.5 minute intervals, and the measurement and sputtering were repeated to obtain data. In addition, each measurement system was performed under the following conditions. <Survey Spectrum> X-ray beam diameter: 100μm (25w15kV) Pass energy: 280eV, 1eV step Line analysis: φ100μm*1200um cumulative number of times 6 times <Narrow spectrum> X-ray beam diameter: 100μm (25w15kV) Pass energy: 112eV, 0.1eV step line analysis: φ100μm*1200um <Ar sputtering conditions> Accelerating voltage 1kV Irradiated area 2x2mm Sputtering speed 2.29nm/min (Calculated by SiO ₂ )

The results of the amount of current dispersion per 4μm ² copper foil, the total area, and the oxygen content at a depth of 5nm are shown in Table 4.

Table 4 Example Types of Copper Foil 3 4 5 6 8 9 Current dispersion Scattered number 1448 827 953 1166 847 510 Total area [nm ² ] 399871 1307973 1254892 981925 877900 2305761 Oxygen amount [atom%] 16 17 18 twenty three 7 5 Comparative example Types of Copper Foil 1 2 3 4 5 Current dispersion Scattered number 0 2 105 0 12 Total area [nm ² ] 0 122 78644 0 1586 Oxygen amount [atom%] 42 40 25 37 26

In this way, the copper foil system of the example has a current dispersion number of 200 or more per 4 μm ² copper foil, and the total area through which current flows is 100,000 nm ² or more. In addition, the oxygen content in any embodiment is 25% or less, which is a preferable value. In the case of Comparative Examples 1, 2, 4, and 5, since the amount of oxygen is large, the total area through which the current flows is small. The small total area through which the current flows means that the current is not easy to flow and the power collection is poor. In the case of Comparative Example 3, although the oxygen content was 25% or less, the amount of current dispersion was small, and the current concentration caused the negative electrode material to peel off, resulting in poor high-speed charge and discharge characteristics.

[Figure 1] A comprehensive table of the processing conditions of the first step and the second step in Example 1 to Example 7 and Comparative Example 1 to Comparative Example 3 of the present invention. [Second Figure] In (A) Examples 1 to 7 and (B) Comparative Examples 1 to 3 of the present invention, scanning electron microscope (SEM) images of the cross section of each copper foil are displayed. (C) is an illustration of the method of calculating the convex part in (A) and (B). An arrow indicates a convex part. In addition, the enlarged diagram in (C) shows an example of the method of measuring "the length of the line segment that extends perpendicular to the minimum point of the concave portion connecting both ends". [Figure 3] In an example of the present invention, a graph showing the coating stability of the solvent-based negative electrode material. [Figure 4] A schematic diagram of a method for measuring the residual rate of negative electrode material in an example of the present invention. [Figure 5] In the embodiment of the present invention, the current image obtained by the atomic force microscope (AFM) is used.

Claims (19)

A copper foil having protrusions with a height of 5 nm or more on at least a part of the surface, and the density of the protrusions in this part is 15 or more and 100 or less per 3.8 μm on average. Such as the copper foil of claim 1, wherein the surface is plated. The copper foil of claim 1 or 2, wherein the density of the protrusions in the part is 20 or more and 62 or less on average per 3.8 μm. The copper foil of any one of claims 1 to 3, wherein the three-point standard deviation σ of the surface roughness Rz of the part is 0.5 or less. The copper foil of any one of claims 1 to 3, wherein the three-point standard deviation σ of the surface roughness Rz of the part is 0.3 or less. The copper foil according to any one of claims 1 to 4, wherein the surface roughness Rz of the part is 2 μm or less on average. The copper foil of any one of claims 1 to 4, wherein the surface roughness Rz of the part is 1.54 μm or less on average. Such as the copper foil of any one of claims 1 to 7, wherein the calculated number of currents per 4 μm ² by binarization treatment is an average of 200 or more. Such as the copper foil of any one of Claims 1 to 7, wherein the calculated number of currents to be binarized per 4 μm ² is an average of 500 or more. Such as the copper foil of any one of claims 1 to 9, wherein the total area of current per 4 μm ² is an average of 100,000 nm ² or more. Such as the copper foil of any one of claims 1 to 9, wherein the total current area per 4 μm ² is an average of 300,000 nm ² or more. The copper foil of any one of claims 1 to 11, wherein, when measured by X-ray photoelectron spectroscopy, the oxygen content at 5 nm from the surface in the depth direction is 50% or less. The copper foil according to any one of claims 1 to 11, wherein, when measured by X-ray photoelectron spectroscopy, the oxygen content at 5 nm from the surface in the depth direction is 25% or less. The copper foil according to any one of claims 1 to 13, wherein at least a part of the surface is formed with a metal layer other than copper. Such as the negative electrode current collector of claim 14, wherein the thickness of the metal layer is 15 nm or more and 200 nm or less. A negative electrode current collector of a lithium ion battery, comprising the copper foil according to any one of claims 1 to 7. A negative electrode current collector of a lithium ion battery, comprising the copper foil according to any one of Claims 8-15. A method for manufacturing a negative electrode current collector of a lithium ion battery, which is the method for manufacturing a negative electrode current collector of a lithium ion battery as described in claim 7, comprising: a method selected from sodium chlorite, sodium hypochlorite, potassium chlorate and potassium perchlorate The first step of oxidizing the copper surface of the copper foil with more than one oxidant to form protrusions; The second step of plating the oxidized copper surface; and The third step of manufacturing a negative electrode current collector using the copper foil after the copper surface is plated. The method for manufacturing a negative electrode current collector of a lithium ion battery according to claim 18, wherein, before the second step, it further includes a step of dissolving the copper surface oxidized in the first step and/or a second step of reducing Four steps.

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