KR20220002243A - Copper foil and negative electrode current collector of lithium ion battery comprising same, and method for manufacturing the same - Google Patents

Abstract

An object of the present invention is to provide a novel copper foil, a negative electrode current collector of a lithium ion battery including the same, and a method for manufacturing the same. In one embodiment of the present invention, at least a part of the surface has convex portions with a height of 5 nm or more, and a copper foil having a density of 15 or more and 100 or less per 3.8 μm is manufactured, and the negative electrode current collector is manufactured using the copper foil. manufacture

Description

Copper foil and negative electrode current collector of lithium ion battery comprising same, and method for manufacturing the same

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

In the anode current collector of a lithium ion battery (LIB), if a large-capacity active material is employed for high output and high energy density, the expansion rate of the active material volume increases during charging and discharging. Therefore, when charging and discharging are repeated, the binder connecting the active material and the current collector is broken, or the binder is peeled off from the interface of the active material and the current collector, thereby deteriorating cycle characteristics. In order to prevent this, an invention of improving the adhesion between the copper foil and the negative electrode mixture layer by increasing the amount of the binder on the copper foil side has been disclosed (Japanese Patent Application Laid-Open No. 10-284059). In addition, there is disclosed an invention for improving the adhesion between copper foil and an active material by forming a mustache-shaped copper oxide on the surface of the copper foil to increase the surface area (Japanese Patent Application Laid-Open No. Hei 11-307102)

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

One embodiment of the present invention is a copper foil in which at least a portion of the surface has convex portions with a height of 5 nm or more, and in the portion, the density of the convex portions is 15 or more and 100 or less on average per 3.8 μm. The surface may be plated. In some of the above, the density of the convex portions may be 20 or more and 62 or less on average per 3.8 μm. Further, the three-point standard deviation σ of the partial surface roughness Rz may be 0.5 or less, or 0.3 or less. Moreover, 2 micrometers or less may be sufficient as the average of the said part surface roughness Rz, and 1.54 micrometers or less may be sufficient as it. The average number of measurements of the amount of current by binarization per 4 µm ^{2 of copper foil may be 200 or more or 500 or more.} Copper foil 4μm total current average area 100000nm may be ² or more than ² 300000nm or more per ^second. As measured by X-ray photoelectron spectroscopy (XPS), the amount of oxygen in the depth direction 5 nm from the surface may be 50% or less or 25% or less. A metal layer other than copper may be formed on at least a part of the surface. 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 comprising the copper foil of any one of the above.

Another embodiment of the present invention is a method for manufacturing a negative electrode current collector of a lithium ion battery comprising the copper foil of any one of the above, and is selected from sodium chlorite, sodium hypochlorite, potassium chlorate, potassium perchlorate, and potassium persulfate. 1st process of oxidizing the copper surface of copper foil with one or more oxidizing agents, and forming a convex part; a second step of plating the oxidized copper surface; and a third step of manufacturing a negative electrode current collector using the copper foil on which the copper surface is plated. Before the second process, a process of dissolving and/or reducing the copper surface oxidized in the first process may be further included.

In addition, in this specification, let an average value be an average when multiple points|pieces, for example, 3 points|pieces are measured at random.

According to the present invention, it has become possible to provide a novel copper foil, a negative electrode current collector of a lithium ion battery including the same, and a method for manufacturing the same.

1 is a table summarizing the treatment conditions in the first step and the second step in Examples 1 to 7 and Comparative Examples 1 to 3 of the present invention.
2 is a scanning electron microscope (SEM) image showing a cross section of each copper foil in (A) Examples 1 to 7 and (B) Comparative Examples 1 to 3 of the present invention. (C) is an image showing an example of a method of counting the convex portions in (A) and (B). One arrow indicates one convex portion. In addition, in the enlarged view in (C), an example of a method of measuring the 'length extending perpendicularly to the line segment connecting the minimum points of the concave portions at both ends' is shown.
3 is a view showing the application stability of the solvent-based negative electrode material in the embodiment of the present invention.
4 is a view showing a method of measuring the negative electrode material residual ratio in the embodiment of the present invention.
5 is a current image obtained using an atomic force microscope (AFM) in an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to Examples. In addition, the objects, features, advantages and ideas of the present invention are apparent to those skilled in the art from the description of the present specification, and those skilled in the art can easily reproduce the present invention from the description of the present specification. Embodiments and specific examples of the present invention described below represent preferred embodiments of the present invention, are shown for illustration or description, and do not limit the present invention to these. It is apparent to those skilled in the art that various modifications can be made based on the description of the present specification within the spirit and scope of the present invention disclosed herein.

==Copper Foil==

The copper foil disclosed in this specification may be a rolled copper foil, an electrolytic copper foil may be sufficient, and copper alloy foil may be sufficient as it. The copper content or purity is preferably high, preferably 50% or more, more preferably 60% or more, more preferably 70% or more, more preferably 80% or more, more preferably 90% or more, It is more preferable that it is 95 % or more, It is more preferable that it is 98 % or more, It is still more preferable that it is 99.5 % or more. The thickness of the copper foil is not particularly limited, but it is preferably a thickness used for a negative electrode current collector of a lithium ion battery, for example, 5 μm to 100 μm, and the thickness of the copper foil according to the use can be selected from the range. can In addition, the surface roughness of the copper foil is not particularly limited, and any copper foil of any roughness can be used, but if the surface roughness is too large, the tensile strength is lowered or the negative electrode material is not filled to the uneven bottom, so that the adhesion is lowered. In addition, when the number of convex portions is small while the surface roughness is large, electricity is concentrated in the convex portions and deterioration of battery characteristics occurs due to peeling of the active material. Therefore, the surface roughness is preferably 2 µm or less.

In the cross-sectional image of this copper foil taken by a scanning electron microscope, at least a part of the surface has convex parts with a height of 5 nm or more, and the density of the convex parts averages 15 to 100 per 3.8 μm measured in a direction parallel to the surface. It is preferable that they are below, and it is more preferable that they are an average of 20 or more and 62 or less. The number of convex parts is counted as a convex part when the length extending perpendicularly to the line segment connecting the minimum points of the concave parts at both ends of the convex part is 5 nm or more on the scanning electron microscope cross-section imaging. The height of the convex portion can be calculated by Rz defined in JIS B 0601:2001 using a scanning electron microscope, particularly a confocal scanning electron microscope.

It is preferable that it is 0.5 or less, and, as for the three-point standard deviation (sigma) of the surface roughness Rz of a part of surface with a convex part 5 nm or more in height, it is more preferable that it is 0.3 or less. As the three-point standard deviation σ of Rz decreases, the unevenness becomes more uniform. And it is preferable that it is 2 micrometers or less, and, as for the average of Rz, it is more preferable that it is 1.54 micrometers or less. The smaller the average of Rz, the smaller the unevenness.

These properties are preferable structures in using copper foil for a negative electrode current collector. Although there is no particular restriction on the principle, when the number of convex portions is small, the surface area of the copper foil becomes small, so the adhesion of the copper foil to the negative electrode deteriorates, and as a result, the holding capacity becomes low. When the number of convex portions is small, it is necessary to increase Rz in order to increase the surface area. When Rz becomes large, current is concentrated on the convex portions, so that the copper foil and the active material are easily peeled off, and the capacity retention rate becomes small. In addition, even when the three-point standard deviation of the surface roughness Rz, that is, non-uniformity is large, current concentration tends to occur when used for a negative electrode current collector, and as a result, the capacity retention rate is lowered.

As the negative electrode current collector, for example, current concentration can be suppressed as the number of current dispersion increases, and peeling of the negative electrode material is less likely to occur. Accordingly, the capacity retention rate is excellent in the high-speed charge/discharge characteristic (C-rate). Copper foil 4μm average number per ^second of the number of current distribution is preferably less than 200, more preferably, preferred, and more than 500 more preferably greater than 400. That is, the density of the current dispersed water ^{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 threshold value is equal to or greater than a certain amount of current, the easier the flow of electricity is and the better the power collection is. The copper foil 4μm ² Average total area party, it is preferable 100000nm least ^2, more preferably at least 200000nm ^2, more preferably not less than 300000nm ^2. That is, the ratio of the area through which the current flows when a certain amount of current or more is set 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 constant current is, for example, 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 by a well-known method, for example, the method described in an Example.

When the amount of oxygen contained in the negative electrode material is large, resistance increases, so that it becomes difficult to flow an electric current. Therefore, in order for the area through which the current flows to be 10000 ^{nm 2} or more, it is preferable that the amount of oxygen contained in the negative electrode material is small, specifically, the amount of oxygen at a depth of 5 nm is preferably 50% or less, and more preferably 40% or less, It is more preferable that it is 35 % or less, and it is still more preferable that it is 25 % or less. In addition, this amount of oxygen can be measured by X-ray photoelectron spectroscopy (XPS).

In addition, since a metal layer other than copper is formed on the surface, the current dispersibility becomes good, the current flows more easily, and oxidation of the surface can be prevented, so that the change of the contact angle with respect to water is difficult to occur with time. For this reason, it is preferable that the metal layer is formed in the surface. As the metal other than copper, tin, silver, zinc, aluminum, titanium, bismuth, chromium, iron, cobalt, nickel, palladium, gold, platinum or various alloys can be used. A plating process can be used for formation of this metal layer, for example. It is preferable that they are 15 nm or more and 200 nm or less, and, as for the thickness of a metal layer, it is more preferable that they are 30 nm or more and 200 nm or less. When it is less than 15 nm, it becomes easy to generate a change with time, and when it exceeds 200 nm, since the unevenness|corrugation is filled by leveling, the number of current dispersion also decreases, and it becomes easy to generate|occur|produce current concentration.

==Manufacturing method of copper foil and negative electrode current collector of lithium ion battery==

The manufacturing method of the copper foil disclosed in this specification is a 1st process of oxidizing the copper surface of copper foil to form a fine convex part; 2nd process of further adjusting the convex part formed in the surface of the oxidized copper foil; The 3rd process of manufacturing the negative electrode collector of the lithium ion battery using the copper foil which adjusted the convex part on the copper surface; it includes. In addition, the second process includes at least one process of plating, reducing, or dissolving the oxidized copper surface. Hereinafter, each process will be described in detail.

(1) 1st process (oxidation process)

At a 1st process, first, the copper surface of copper foil is oxidized using an oxidizing agent, and while forming the layer containing copper oxide, a convex part is formed in the surface.

The oxidizing agent is not particularly limited, and for example, an aqueous solution or buffer solution such as sodium chlorite, sodium hypochlorite, potassium chlorate, potassium perchlorate, or potassium persulfate can be used, but an aqueous solution containing sodium chlorite or sodium hypochlorite is used. it is preferable If these are used, a desirable surface shape can be formed. Various additives (for example, phosphate salts such as trisodium phosphate dodecahydrate or surface active molecules) may be added to the oxidizing agent. Examples of the surface-active molecules include porphyrins, porphyrin large ring, expanded porphyrin, ring-reduced porphyrin, linear porphyrin polymer, porphyrin sandwich coordination complex, porphyrin sequence, silane, tetraorgano-silane, aminoethyl-aminopropyl-tri Methoxysilane, (3-aminopropyl)trimethoxysilane, (1-[3-(trimethoxysilyl)propyl]urea)((l-[3-(Trimethoxysilyl)propyl]urea)), (3- Aminopropyl) triethoxysilane, ((3-glycidyloxypropyl) trimethoxysilane), (3-chloropropyl) trimethoxysilane, (3-glycidyloxypropyl) trimethoxysilane, dimethyl Dichlorosilane, 3-(trimethoxysilyl)propyl methacrylate, ethyltriacetoxysilane, triethoxy(isobutyl)silane, triethoxy(octyl)silane, tris(2-methoxyethoxy)(vinyl) ) silane, chlorotrimethylsilane, methyltrichlorosilane, silicon tetrachloride, tetraethoxysilane, phenyltrimethoxysilane, chlorotriethoxysilane, ethylene-trimethoxysilane, amine, sugar and the like. Moreover, you may contain alkaline compounds, such as sodium hydroxide and potassium hydroxide, other than an oxidizing agent.

As an additive used in this oxidation step, it is preferable to appropriately suppress the formation of convex portions on the surface due to oxidation, such as a silane coupling agent containing a silicon compound. become more uniform. By manufacturing the electrical power collector of a lithium ion battery using the copper foil with a uniform height of the convex part on the surface, it becomes possible to reduce the partial nonuniformity of the negative electrode material application amount with respect to an unevenness|corrugation. Thereby, the non-uniformity in the manner of flowing the current is eliminated, and the battery characteristics are also improved. And productivity is also improved.

Although the oxidation reaction conditions are not specifically limited, It is preferable that it is 40-95 degreeC, and, as for the liquid temperature of an oxidizing agent, it is more preferable that it is 45-80 degreeC. It is preferable that it is 0.5 to 30 minutes, and, as for reaction time, it is more preferable that it is 1 to 10 minutes.

In addition, before this oxidation process, degreasing by alkali treatment or washing by acid treatment may be performed as pretreatment. The specific method of alkali treatment or acid treatment is not particularly limited, but alkali treatment is, for example, preferably 30 to 50 g/L, more preferably 40 g/L of an aqueous alkali solution, for example, 30 to 50 g of sodium hydroxide aqueous solution. It can be carried out by treating with water at ℃, about 0.5 to 2 minutes, and then washing with water. In addition, the acid treatment can be performed, for example, by immersing the copper surface in sulfuric acid having a liquid temperature of 20 to 50° C. and 5 to 20% by weight for 1 to 5 minutes, followed by washing with water. After the acid treatment, in order to reduce the treatment unevenness and to prevent mixing of the acid used in the washing treatment with the oxidizing agent, a weak alkali treatment may be performed again. This alkali treatment is not particularly limited, but preferably 0.1 to 10 g/L, more preferably 1 to 2 g/L of an aqueous alkali solution, for example, an aqueous sodium hydroxide solution at 30 to 50° C. for about 0.5 to 2 minutes. can be done In addition, as a pretreatment, a treatment for physically roughening the copper surface, such as etching, may be performed. At this time, since the shape of the convex portion formed on the copper surface generally depends on the crystallinity of the copper to be treated, physical roughening treatment It does not become fine unevenness|corrugation only by itself, and in order to obtain the copper foil which has fine unevenness|corrugation, it is necessary to go through this oxidation process.

(2) second process

A 2nd process contains the at least 1 process of (2-1) plating process process, (2-2) reduction process process, and (2-3) dissolution process process. The plating process may be performed after the reduction process or after the dissolution process. Although the copper surface is roughened so that it may have a fine convex part by the oxidation treatment in a 1st process, the convex part formed in the copper surface by the 2nd process of this invention is further adjusted. Each process of the 2nd process is demonstrated below.

(2-1) Plating process

In this process, the oxidized copper surface is plated with metals other than copper, and the convex part of the oxidized copper surface is adjusted. As the plating method, a known technique may be used. For example, as a metal other than copper, tin, silver, zinc, aluminum, titanium, bismuth, chromium, iron, cobalt, nickel, palladium, gold, platinum, or various alloys may be used. can The plating method is not particularly limited, either, and plating can be performed by electrolytic plating, electroless plating, vacuum vapor deposition, chemical conversion treatment, or the like. Electrolytic plating is preferable, and it is easy to reduce to metallic copper and has excellent power collection compared to electroless plating.

In the case of electroless nickel plating, it is preferable to perform treatment using a catalyst. As the catalyst, it is preferable to use iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium and salts thereof. As a reducing agent used in the case of electroless nickel plating, it is preferable to use a reducing agent in which copper and copper oxide do not have catalytic activity. As a reducing agent in which copper and copper oxide do not have a catalytic activity, hypophosphite, such as sodium hypophosphite, is mentioned.

Thus, by obtaining the metal layer which maintained the fine unevenness|corrugation formed in the 1st process, the surface is protected and the aging stability of composite copper foil improves. The thickness of the plating is not particularly limited, but if it is too thick, RSm becomes small by reducing the number of convex portions by leveling, and the surface area decreases, and at the same time, the battery characteristics deteriorate due to a decrease in the current collecting power, so 1 μm or less is preferable.

In a plating processing process, unless copper purity is raised, Preferably it is not made into pure copper, it is difficult to make plating uniformly. Therefore, it is common to perform plating by removing the oxide film on the surface. In the method of the present disclosure, by forming a desirable shape with an oxide film and then performing a plating treatment, adhesion and battery characteristics necessary for manufacturing a current collector of a lithium ion battery can be obtained.

(2-2) reduction treatment process

In this process, the copper oxide formed in copper foil is reduced using the chemical|medical solution (reduction|reduction chemical|medical solution) containing a reducing agent, and the number and length of unevenness are adjusted.

As a reducing agent, DMAB (dimethylamine borane), diborane, sodium borohydride, hydrazine, etc. can be used. In addition, the chemical|medical solution for reduction 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 process

In this process, the oxidized copper surface is melt|dissolved with a dissolving agent, and the convex part of the oxidized copper surface is adjusted. Although the solubilizing agent used in this process is not specifically limited, A chelating agent, a biodegradable chelating agent, etc. can be illustrated. Specifically, EDTA (ethylenediamine tetraacetic acid), DHEG (diethanol glycine), GLDA (L-glutamic acid diacetic acid tetrasodium), EDDS (ethylenediamine-N, N'-disuccinic acid), HIDS (3-hyd Sodium hydroxy-2,2'-iminodisuccinate), MGDA (methyl glycine trisodium diacetate), ASDA (aspartate diacetic acid 4Na), HIDA (N-2-hydroxyethyliminodiacetic acid disodium salt), sodium gluconate, ethide ronic acid (hydroxyethanediphosphonic acid); and the like.

The pH of the solubilizing agent is not particularly limited, but in acid, since the amount of dissolution is large, it is difficult to control the treatment, and treatment unevenness tends to occur. It is more preferable that it is pH 9.0-10.5, and it is still more preferable that it is pH 9.8-10.2.

In this process, the copper surface is treated until the dissolution rate of copper oxide is 35 to 99%, preferably 50 to 99%, and the thickness of CuO is 4 to 300 nm, preferably 8 to 200 nm. In addition, the thickness of CuO can be measured by SERA (manufactured by ECI). Under this condition, since the number and length of the surface asperity becomes preferable and the treatment unevenness is reduced, it is preferable to conduct a pilot experiment in advance to set conditions such as temperature and time so that such a layer of copper oxide is obtained. In addition, a dissolution rate means the ratio of the copper oxide which melt|dissolved and removed from the copper surface among the copper oxides of a copper surface.

Thus, by performing a 2nd process with respect to copper foil, the composite copper foil suitable for the negative electrode collector of the lithium ion battery with which the convex part on the surface was adjusted can be manufactured.

A coupling treatment using a silane coupling agent or the like, a chromate treatment, or a rust prevention treatment using benzotriazoles may be performed on the copper foil produced in these second steps.

(3) 3rd process (negative electrode current collector manufacturing process)

Using the copper foil treated as described above, a negative electrode current collector for a lithium ion battery may be manufactured according to a known method, and a negative electrode may be manufactured. For example, a negative electrode material containing a carbon-based active material is prepared and dispersed in a solvent or water to obtain an active material slurry. After this active material slurry is applied to a copper foil, it is dried in order to evaporate a solvent or water. Then, after pressing and drying again, the negative electrode collector is shape|molded so that it may become a desired shape. In addition, the negative electrode material may include silicon, a silicon compound, germanium, tin, lead, and the like having a theoretical capacity greater than that of the carbon-based active material. Further, as the electrolyte, not only an organic electrolyte in which a lithium salt is dissolved in an organic solvent, but also a polymer made of polyethylene oxide or polyvinylidene fluoride may be used. It can be applied not only to lithium ion batteries but also to lithium ion polymer batteries.

Example

[Roughening treatment of evaluation copper foil and copper foil surface]

The processing of the base material was performed using the following copper foils as an Example and a comparative example.

In Examples 1-3, the surface treatment layer of the mat surface of a commercially available copper foil (B-Foil by Targray) was removed, and various surface treatments were performed. In Examples 4-7, the surface treatment layer of commercially available copper foil (Furukawa Electric Co., Ltd. product NC-WS) was removed, and the surface treatment mentioned later was performed. Comparative Example 1 is a mat surface of a commercially available copper foil (B-Foil manufactured by Targray), Comparative Example 2 is a commercially available copper foil (NC-WS manufactured by Furukawa Denki Kogyo Co., Ltd.), Comparative Example 3 is a commercially available copper foil (Targray) The shiny surface (cathode contact surface) of product B-Foil) was used.

In addition, the processing conditions in a 1st process and a 2nd process were put together in the table|surface of FIG. As the pretreatment conditions and the application conditions of the negative electrode material, the same conditions were used in Examples and Comparative Examples.

(1) Pretreatment

[Alkaline degreasing treatment]

After immersing copper foil in the sodium hydroxide aqueous solution of 50 degreeC liquid temperature and 40 g/L for 1 minute, water washing was performed.

[acid washing treatment]

After the copper foil subjected to alkaline degreasing treatment was immersed in an aqueous solution of sulfuric acid having a liquid temperature of 25°C and 10 wt% for 2 minutes, water washing was performed.

[Predip processing]

The copper foil which performed the acid washing process was immersed for 1 minute in the liquid temperature 40 degreeC, and the chemical|medical solution for predip of sodium hydroxide (NaOH) 1.2g/L.

(2) 1st process (oxidation treatment)

First, about the copper foil of Example 1, Example 2, Example 3, Example 4, Example 5, and Example 7 as a 1st process, aqueous alkali solution (20 g/L sodium hydroxide, 60 g/L sodium chlorite , 2 g/L 3-glycidyloxypropyltrimethoxysilane). The treatment temperature and treatment time were 1 minute at 45°C for Example 1, 2 minutes at 73°C for Examples 2, 3, 4, and 7, and 3 minutes at 73°C for Example 5.

About the copper foil of Example 6, 73 degreeC and 8 minutes oxidation treatment were performed with aqueous alkali solution (20 g/L sodium hydroxide, 60 g/L sodium chlorite). In addition, surface treatment, such as oxidation treatment of this invention, was not performed to the copper foil of Comparative Examples 1-3.

(3) 2nd process

Next, with respect to the copper foil which performed the oxidation process of the 1st process as a 2nd process, (3-1) dissolution process, (3-2) plating process, and (3-3) reduction process are each 1 or more types of processes. performed

(3-1) dissolution treatment

About the copper foil of Example 2, Example 3, and Example 7, after the oxidation treatment of (2), the dissolution treatment was performed at 55 degreeC using the solvent L-glutamic acid tetrasodium diacetate (38 g/L). . The treatment time was 1 minute for Example 2, 2 minutes for Example 3, and 3 minutes for Example 7.

(3-2) Plating

After the oxidation treatment of (2) for the copper foils of Examples 1 and 4, and after the dissolution treatment of (3-1) for the copper foils of Examples 2 and 3, the electrolytic solution for nickel plating (450 g/L) Electrolytic plating was performed using nickel sulfamic acid, 40 g/L boric acid). The current density was 1 (Å/dm 2 ) and the time was 15 (sec). No plating treatment was performed on the other copper foils.

(3-3) reduction treatment

For the copper foils of Examples 5 and 6, after the oxidation treatment of (2), a reduction treatment was performed by using a solvent (5 g/L dimethylamine borane, 5 g/L sodium hydroxide) and allowing it to stand at room temperature for 3 minutes. .

(4) Measurement of height and number of convex portions, and surface roughness

When the cross section of the copper foil which performed the process of (1)-(3) was observed with the scanning microscope (SEM), the photograph of FIG.2(A), FIG.2(B) was obtained. Using this photographed image, the number of convex portions in the cross section was measured. The number of convexities was counted as a convex part when the length extending perpendicularly to the line segment connecting the minimum points of the concave parts at both ends of the convex part on the scanning electron microscope cross-section was 5 nm or more. An example of a counting method (counting Example 5) is shown in FIG. 2(C).

In addition, the surface roughness Rz was measured using the confocal scanning electron microscope OPTELICS H1200 (Lasertec Corporation (Lasertec Corporation) product), and it computed by Rz determined by JIS B0601:2001. As measurement conditions, the scan width was set to 100 µm, the scan type was set to area, the light source was set to Blue, and the cutoff value was set to 1/5. The object lens was set to x100, the contact lens to x14, the digital zoom to x1, and the Z-pitch to be set at 10 nm. Data for three parts were acquired, and the standard deviation was calculated. In addition, Rz was made into the average value of three parts.

(Table 1)

As described above, all samples of Examples had an average of 10 or more protrusions per 3.8 μm in height of 5 nm or more, an average Rz of 2.00 μm or less, and the standard deviation was 0.3 or less.

(5) Application of negative electrode material

(5-1) Application of water-based negative electrode material

The copper foils of Example 1, Example 2, Example 3, and Comparative Example 1 were used for evaluation.

Graphite (EQ-Lib-MCMB from MTI), Acetylene Black (Li-400 from Denka Company Limited), CMC (Carboxymethyl Cellulose CMC Daicel 2200 from Daicel FineChem Ltd.), SBR ( Styrene-butadiene rubber BM-400B manufactured by Zeon Corporation) and Si (manufactured by Tekna Advanced Materials) are mixed with a predetermined mixture (graphite: 86.5% by weight, acetylene black: 1.5% by weight, CMC: 5.0% by weight, SBR: 2.5% by weight) %, Si: 4.5 wt%), and the viscosity was adjusted using pure water.

Thereafter, the mixture was stirred with a planetary stirring device until graphite, acetylene black, CMC, and Si became uniform, and finally SBR was added to further stir. It applied to copper foil by setting it so that the coating thickness might become 150 micrometers in thickness with a bar coater. After application, it was dried at 70° C. for 2 hours to remove moisture, and pressing was performed so that the thickness of the negative electrode material became 30 μm using a roll press to adhere the copper foil to the negative electrode material. Thereafter, drying was performed at 70° C. for 12 hours with a vacuum and a reduced pressure dryer.

(5-2) Application of solvent-based negative electrode material

The copper foils of Example 4, Example 5, Example 6, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were used for evaluation.

Graphite (manufactured by Nippon Graphite), acetylene black (Li-400 manufactured by Denka), and PVDF (polyvinylidene fluoride L#1120 manufactured by Kureha Corporation) are used in a prescribed formulation (graphite: 85 weight) %, acetylene black: 5 wt%, PDVF: 10 wt%). The viscosity was adjusted using NMP as a solvent.

Then, it stirred with a planetary stirring device until graphite, acetylene black, and PVDF became uniform, and it applied to copper foil by setting so that the coating thickness might become 150 micrometers with a bar coater. After application, it was dried at 80° C. for 2 hours to remove the solvent, and pressing was performed so that the thickness of the negative electrode material was 30 μm using a roll press to adhere the copper foil to the negative electrode material. Thereafter, drying was performed at 120° C. for 12 hours with a vacuum and a reduced pressure dryer.

3 is a view showing the application stability of the solvent-based negative electrode agent. The left side of FIG. 3 is Example 4, and since there are many convex parts, adhesiveness is favorable and the negative electrode agent is apply|coated uniformly by capillary phenomenon. On the other hand, the right side of FIG. 3 is Comparative Example 1, and since the number of convex parts was small, neither adhesiveness nor capillary phenomenon was obtained, but peeling arose partly a lot.

(6) Coin cell fabrication

For the production of the coin cell, the sample prepared in (5) Application of the negative electrode material was used for the negative electrode. 1M LiPF6/EC-DEC (1:1) was used for the coin cell as an electrolyte, and the coin cell was produced using the negative electrode, the separator, and lithium foil.

(7) Measurement of charge/discharge characteristics

After manufacturing SEI (Solid Electrolyte Interphase), a thin film formed on the surface of the anode by reduction decomposition of the electrolyte at 0.2C, 1 cycle, discharge is in CC-CV (voltage 10mV, current up to 0.1C) mode, and charging is CC (voltage 1500mV). Until) mode, repeat 1C⇒3C⇒5C⇒1C for 3 cycles each at 30℃, then repeat 1C⇒3C⇒5C⇒1C for 3 cycles each at 50℃ in the same way at 50℃, the 3rd cycle of 5C at 50℃ properties were evaluated.

(8) Measurement of anode material residual rate

As adhesive evaluation, the negative electrode material residual rate was computed using the copper foil after application|coating of the negative electrode material of (5). First, the weight of the copper foil coated with the negative electrode material is measured. Thereafter, a double-sided tape is applied to the plate for fixing, and the cellophane tape is attached thereon so that the adhesive side of the cellophane tape is in contact with the negative electrode material, and then, the negative electrode material side of the copper foil coated with the negative electrode material is in contact with the cellophane tape After applying a pressure of 5 kN/inch2, it was peeled off under 90° peel strength test conditions (JIS 0237:2009) with a peel strength tester (manufactured by Imada), and the amount of negative electrode material remaining on the copper foil side was measured. . The test method is shown in FIG. 4 .

The negative electrode material residual ratio was computed using the following formula.

Negative electrode material residual ratio [%] = (total weight after test - weight of copper foil) / (total weight before test - weight of copper foil) × 100

Table 2 shows the evaluation results with the aqueous negative electrode material. Table 3 shows the evaluation results with the solvent-based negative electrode material.

(Table 2)

(Table 3)

In this way, by manufacturing a negative electrode current collector of a lithium ion battery using a copper foil having convex portions with a height of 5 nm or more on at least a part of the surface and having an average density of 15 or more and 100 or less per 3.8 μm, the copper foil and the negative electrode Adhesion and capacity retention are improved.

(9) Measurement of current dispersion number and area

The sample copper foil is an example, and in addition to Examples 3 to 6, under the same conditions as in Example 1, only the plating processing time is lengthened, and the plating thickness is 100 nm (Example 8), 200 nm by adjusting the Coulomb amount at the time of plating A copper foil was used as (Example 9), and as a comparative example, in addition to Comparative Examples 1 to 3, a commercially available copper foil (NC-WS manufactured by Furukawa Denki Kogyo Co., Ltd.) was subjected to the same oxidation treatment as in Example 1 Under the same conditions as in Example 1 (Comparative Example 4) and in Example 1, only the plating time was shortened and the plating thickness was 10 nm (Comparative Example 5). In addition, it was set as the average thickness of the perpendicular|vertical direction of plating as plating thickness here. That is, copper foil is dissolved in 12% nitric acid, and the solution is analyzed using an ICP emission spectrometer 5100SVDV ICP-OES (manufactured by Agilent Technologies) to measure the concentration of metal used for plating, By considering the density of the metal and the surface area of the metal layer, the average thickness of the metal layer at the time of forming a layer was calculated, and it was set as the plating thickness.

About these sample copper foils, the current image of FIG. 5 was obtained on the following measurement conditions using an atomic force microscope (AFM). Adjustments were made so that only the current value of -60 nA or less was displayed on the obtained current. In addition, in this measurement, in order to remove the influence on the electric current phase by oxidation of the copper foil surface, the bias voltage is made into negative. Therefore, a negative current value means that the resistance value is small and the current flows more easily.

Apparatus: Product of Hitachi High-Tech Science Corporation

Probe Station AFM5000II

Connection model: AFM5300E

Cantilever: SI-DF3-R

Set using the auto setup function on the AFM5000II

(Amplitude attenuation rate, scan frequency, I gain, P gain, A gain, S gain)

Scanning area: 2μm everywhere

Number of pixels: 512x512

Measurement mode: Current (nano)

Measuring field of view: 2μm

SIS Mode: Enabled

Scanner: 20μm scanner

Bias voltage: -0.5V

Measuring atmosphere: vacuum

The obtained current image was converted to a monochrome image using image processing software (WINROOF2018, manufactured by MITANI CORPORATION), and then binarized, and the number of current parts (green part) per ^{4μm 2 of copper foil, total area} was measured.

(10) oxygen ratio at 5 nm depth

The oxygen ratio at a depth of 5 nm from the surface of the cathode body was measured by X-ray photoelectron spectroscopy (XPS).

Quantera SXM (manufactured by ULVAC-PHI) as a measuring device and monochromatic AlKα (1486.6 eV) as excitation X-rays were used. For all elements detected in the Survey Spectrum, a Narrow Spectrum was obtained. In the depth direction, Ar sputtering was performed 12 times at 2.5-minute intervals, and data were acquired by repeating measurement and sputtering.

In addition, each measurement was performed under the following conditions.

<Survey spectrum>

X-ray beam diameter: 100 μm (25w15kV)

Pass Energy: 280 eV, 1 eV step

Line analysis: φ100μm*1200um

6 integration times

<Narrow spectrum>

X-ray beam diameter: 100 μm (25w15kV)

Pass Energy: 112 eV, 0.1 eV steps

Line analysis: φ100μm*1200um

<Ar sputter condition>

Acceleration voltage 1kV

irradiation area 2x2mm

Sputtering rate 2.29 nm/min (in terms _{of SiO 2 )}

Table 4 shows the results of the number of current dispersions per 4 µm ^{2 of} copper foil and the oxygen content in the total area and 5 nm depth.

(Table 4)

In this manner, in the embodiment, a copper foil, a copper foil 4μm current spreading over the number of 200 per ^second, the total area in which a current flows is at least ^two 100000nm. In addition, in all cases of Examples, the oxygen content was a preferable value of 25% or less. In Comparative Examples 1, 2 and 4, 5, since the amount of oxygen is large, the total area through which current flows is small. The small total area through which the current flows means that the current hardly flows and the power collection is low. In the case of Comparative Example 3, although the amount of oxygen is 25% or less, since the number of current dispersion is small, the negative electrode material is peeled off because the current is concentrated, and the high-speed charge/discharge characteristic is deteriorated.

Claims (19)

At least a part of the surface has a convex part with a height of 5 nm or more,
In some of the above, the copper foil having an average density of 15 or more and 100 or less per 3.8 μm of the convex portions. According to claim 1,
A copper foil on which the surface is plated. 3. The method of claim 1 or 2,
In some of the above, the copper foil having an average density of 20 or more and 62 or less per 3.8 μm of the convex portions. 4. The method according to any one of claims 1 to 3,
The copper foil whose three-point standard deviation (sigma) of the said part surface roughness Rz is 0.5 or less. 4. The method according to any one of claims 1 to 3,
The copper foil whose three-point standard deviation (sigma) of the said part surface roughness Rz is 0.3 or less. 5. The method according to any one of claims 1 to 4,
Copper foil whose average of said one part surface roughness Rz is 2 micrometers or less. 5. The method according to any one of claims 1 to 4,
Copper foil whose average of said one part surface roughness Rz is 1.54 micrometers or less. 8. The method according to any one of claims 1 to 7,
Copper foil whose average number of measurements of the amount of current by binarization is 200 or more per ^{4 µm 2 of copper foil.} 8. The method according to any one of claims 1 to 7,
Copper foil with an average of 500 or more of the number of measurements of the amount of current by binarization per ^{4 μm 2 of the copper foil.} 10. The method according to any one of claims 1 to 9,
Copper foil with an average total current area of 100000 nm ^{2 or more per 4 μm 2 of} copper foil. 10. The method according to any one of claims 1 to 9,
Copper foil with an average total current area of 300000 nm ^{2 or more per 4 μm 2 of} copper foil. 12. The method according to any one of claims 1 to 11,
Copper foil whose oxygen content in 5 nm depth direction from the surface is 50 % or less when it measures by X-ray photoelectron spectroscopy (XPS). 12. The method according to any one of claims 1 to 11,
Copper foil whose oxygen content at a depth of 5 nm from the surface is 25% or less when measured by X-ray photoelectron spectroscopy (XPS). 14. The method according to any one of claims 1 to 13,
A copper foil in which a metal layer other than copper is formed on at least a part of the surface. 15. The method of claim 14,
The thickness of the metal layer is 15 nm or more and 200 nm or less. The negative electrode current collector of a lithium ion battery comprising the copper foil according to any one of claims 1 to 7. The negative electrode current collector of a lithium ion battery comprising the copper foil according to any one of claims 8 to 15. In the manufacturing method of the negative electrode current collector of the lithium ion battery according to claim 7,
1st process of oxidizing the copper surface of copper foil with one or more oxidizing agents chosen from sodium chlorite, sodium hypochlorite, potassium chlorate, and potassium perchlorate, and forming a convex part;
a second step of plating the oxidized copper surface;
and a third step of manufacturing a negative electrode current collector using the copper foil on which the copper surface is plated. 19. The method of claim 18,
The manufacturing method which further includes the 4th process of melt|dissolving and/or reducing the copper surface oxidized in the said 1st process before the said 2nd process.

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