WO2022054597A1 - Electrolytic copper foil, negative electrode for lithium ion secondary batteries, and lithium ion secondary battery - Google Patents

Abstract

The present invention provides an electrolytic copper foil which is not susceptible to breaking. With respect to this electrolytic copper foil, if t (unit: μm) is the foil thickness, Gs (unit: %) is the gloss of the electrolytic deposition end surface as determined by irradiating the electrolytic deposition end surface with light at an angle of incidence of 60° in the length direction, and E (unit: %) is the elongation as determined by pulling the foil in the length direction, the foil thickness t is from 10 to 20, Gs/t that is obtained by dividing the gloss Gs by the foil thickness t is from 10 to 40, and E/t that is obtained by dividing the elongation E by the foil thickness t is from 0.9 to 1.8.

Description

Electrolytic copper foil, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

The present invention relates to an electrolytic copper foil, a negative electrode for a lithium ion secondary battery using the electrolytic copper foil, and a lithium ion secondary battery including the negative electrode for the lithium ion secondary battery.

A copper foil may be used as a negative electrode current collector of a lithium ion secondary battery, but the copper foil may break due to expansion and contraction of the negative electrode material during charging and discharging of the lithium ion secondary battery. In addition, the copper foil and the negative electrode material that are in close contact with each other are locally peeled off during charging and discharging, and stress during expansion and contraction is concentrated on the peeled portion, so that the copper foil may break.
Patent Documents 1 and 2 disclose an electrolytic copper foil that can be used as a negative electrode current collector of a lithium ion secondary battery. However, the electrolytic copper foil disclosed in Patent Documents 1 and 2 may have insufficient mechanical properties and adhesion to the negative electrode material, and therefore may be broken during charging / discharging of the lithium ion secondary battery. ..

Japanese Patent Publication No. 217787 2007 Japanese Patent Publication No. 204747, 2016

An object of the present invention is to provide an electrolytic copper foil that is less likely to break. Another object of the present invention is to provide a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery in which the negative electrode current collector is less likely to break during charging and discharging.

The electrolytic copper foil according to one aspect of the present invention has a foil thickness of t (unit: μm) and is measured by irradiating light with an incident angle of 60 ° along the length direction with respect to the electrolytic precipitation end surface. When the glossiness of the finished surface is Gs (unit is%) and the elongation measured by pulling along the length direction is E (unit is%), the foil thickness t is 10 or more and 20 or less, and the glossiness Gs. The gist is that Gs / t divided by the foil thickness t is 10 or more and 40 or less, and E / t obtained by dividing the elongation E by the foil thickness t is 0.9 or more and 1.8 or less.

Further, it is a gist that the negative electrode for a lithium ion secondary battery according to another aspect of the present invention includes the electrolytic copper foil according to the above aspect.
Further, it is a gist that the lithium ion secondary battery according to another aspect of the present invention includes a negative electrode for a lithium ion secondary battery according to the other aspect.

The electrolytic copper foil of the present invention is less likely to break. Further, the negative electrode for a lithium ion secondary battery and the lithium ion secondary battery of the present invention are less likely to break in the negative electrode current collector during charging and discharging.

It is a figure explaining the method of manufacturing the electrolytic copper foil using the electrolytic precipitation apparatus, and is the figure explaining the process of performing anodic oxidation. It is a figure explaining the method of manufacturing the electrolytic copper foil using the electrolytic precipitation apparatus, and is the figure explaining the process of performing copper plating.

An embodiment of the present invention will be described. The embodiments described below show an example of the present invention. In addition, various changes or improvements can be added to the present embodiment, and the embodiment to which such changes or improvements are added can also be included in the present invention.
The electrolytic copper foil according to the embodiment of the present invention has a foil thickness of t (unit: μm) and is measured by irradiating light with an incident angle of 60 ° along the length direction with respect to the electrolytic precipitation end surface. When the glossiness of the end surface of the analysis is Gs (unit is%) and the elongation measured by pulling along the length direction is E (unit is%), the foil thickness t is 10 or more and 20 or less, and the glossiness. Gs / t obtained by dividing Gs by the foil thickness t is 10 or more and 40 or less, and E / t obtained by dividing the elongation E by the foil thickness t is 0.9 or more and 1.8 or less.
Due to such a configuration, the electrolytic copper foil of the present embodiment is unlikely to break.

The electrolytic copper foil of the present embodiment can be used as a negative electrode current collector of a lithium ion secondary battery (mainly a cylindrical lithium ion secondary battery). That is, the negative electrode for the lithium ion secondary battery of the present embodiment includes the electrolytic copper foil of the present embodiment. Further, the lithium ion secondary battery of the present embodiment includes the negative electrode for the lithium ion secondary battery of the present embodiment.
Since the electrolytic copper foil of the present embodiment is hard to break, the negative electrode for the lithium ion secondary battery and the lithium ion secondary battery of the present embodiment are hard to break in the negative electrode current collector during charging and discharging.

Hereinafter, the electrolytic copper foil of the present embodiment will be described in more detail.
As a result of diligent studies, the present inventor has made that the electrolytic copper foil having both high stretchability and high glossiness of the electrolytic precipitation end surface expands and contracts even when the negative electrode material expands and contracts during charging and discharging of the lithium ion secondary battery. It was found that breakage is unlikely to occur.

If the electrolytic copper foil has high stretchability, the electrolytic copper foil can follow the expansion and contraction of the negative electrode material, so that breakage is unlikely to occur. Further, if the glossiness is high and the surface is flat, the adhesion between the electrolytic copper foil in close contact and the negative electrode material is uniform over the entire contact surface, and therefore, between the electrolytic copper foil in close contact and the negative electrode material. Local peeling is suppressed during charging and discharging. When local peeling occurs between the electrolytic copper foil and the negative electrode material, the stress at the time of expansion and contraction is concentrated on the peeled portion, so that the electrolytic copper foil is easily broken. Since local peeling is unlikely to occur, breakage is unlikely to occur during charging and discharging.

There is a correlation between the glossiness Gs and the elongation E. The higher the glossiness, the finer the copper crystal grains and the higher the driving force for recrystallization. Therefore, the crystal grain size is increased by the heat softening treatment, and the electrolytic copper foil becomes highly stretchable.
It is known that in electrolytic copper foil, recrystallization of crystal grains progresses at a temperature of about room temperature, and a normal temperature softening phenomenon occurs. However, the finer the crystal grains immediately after precipitation, the greater the driving force for recrystallization. It is considered that the crystal grains after the grain growth is stopped after the softening at room temperature become larger. Therefore, it is considered that if finer crystal grains are precipitated by controlling the thickness of the oxide film described later, the crystal grains inside the electrolytic copper foil after softening at room temperature become larger and the elongation is improved.

In a general double-sided glossy copper foil, the glossiness increases as the foil thickness increases. Therefore, the increase in glossiness is affected by two factors, the contribution due to the densification of the crystal grains inside the electrolytic copper foil and the contribution due to the increase in the foil thickness. Therefore, when estimating the degree of fineness of crystal grains from the glossiness of electrolytic copper foils with different foil thicknesses, the glossiness is standardized by the foil thickness to eliminate the contribution of the foil thickness to the glossiness. It is considered necessary to compare from. Therefore, in the present invention, the parameter Gs / t in which the glossiness Gs is standardized by the foil thickness t is specified.
In addition, two contributions of the foil thickness and the crystal grains can be considered for the elongation, and when estimating the contribution to the elongation of the grain refinement immediately after foil making, the elongation E is standardized by the foil thickness t / E /. It is considered necessary to specify t.
By defining both the parameter Gs / t in which the glossiness Gs is standardized by the foil thickness t and the parameter E / t in which the elongation E is standardized by the foil thickness t, an electrolytic copper foil that is less likely to break can be obtained. It turned out.

[Gs / t]
The parameter Gs / t needs to be 10 or more and 40 or less, but is preferably 25 or more and 40 or less. When the parameter Gs / t is within the above range, the surface of the electrolytic copper foil is flat, so that the adhesive force between the electrolytic copper foil and the negative electrode material tends to be uniform over the entire contact surface. Therefore, local peeling between the electrolytic copper foil and the negative electrode material, which are in close contact with each other, is suppressed during charging / discharging, so that breakage is less likely to occur during charging / discharging. On the other hand, when the parameter Gs / t is within the above range, the adhesive force between the electrolytic copper foil and the negative electrode material is sufficiently exhibited, so that breakage is unlikely to occur during charging and discharging.

The glossiness Gs is measured by irradiating the electrolytic precipitation end surface with light at an incident angle of 60 ° along the length direction, and the glossiness Gs is measured in the "length direction" of the electrolytic copper foil in the present invention. "" Means MD (Machine Direction). For example, when a rotating electrode is used to form a copper foil by plating on the surface of the rotating electrode when manufacturing an electrolytic copper foil, the rotation direction of the rotating electrode is changed. means.

[E / t]
The parameter E / t needs to be 0.9 or more and 1.8 or less, but is preferably 1.2 or more and 1.7 or less, and more preferably 1.3 or more and 1.6 or less. When the parameter E / t is within the above range, the electrolytic copper foil has high stretchability, so that fracture is unlikely to occur during charging and discharging.

[Root mean square root height Sq]
The root mean square height Sq of the electrolytic precipitation end surface of the electrolytic copper foil of the present embodiment measured using a white interference microscope is preferably 0.1 μm or more and 0.4 μm or less, preferably 0.1 μm or more and 0. It is more preferably .25 μm or less.

If the root mean square height Sq of the electrolytic precipitation end surface is within the above range, the adhesion between the electrolytic copper foil and the negative electrode material tends to be higher due to the anchor effect. Further, when the root mean square height Sq of the electrolytic precipitation end surface is within the above range, the electrolytic precipitation end surface is sufficiently flat, so that the adhesion between the electrolytic copper foil and the negative electrode material that are in close contact with each other is strong. It becomes uniform over the entire contact surface. Therefore, local peeling between the electrolytic copper foil and the negative electrode material, which are in close contact with each other, is suppressed during charging / discharging, so that fracture is less likely to occur during charging / discharging.

[Tensile strength]
The electrolytic copper foil of the present embodiment preferably has a tensile strength of 300 MPa or more and 380 MPa or less measured by pulling along the length direction. When the tensile strength is within the above range, the electrolytic copper foil is less likely to break, and the negative electrode material has more excellent followability to expansion and contraction. The definition of "length direction" of the electrolytic copper foil is the same as in the case of glossiness Gs.

The electrolytic copper foil of the present embodiment can be used not only for the negative electrode current collector of the lithium ion secondary battery but also for other purposes. For example, the electrolytic copper foil of the present embodiment can be suitably used for circuit applications. Since the adhesion between the electrolytic copper foil and the resin tends to be uniform over the entire adhesion surface, wrinkles are suppressed from being generated on the electrolytic copper foil at high temperatures, and swelling due to local non-uniformity of the adhesion is caused. The occurrence of defects is suppressed.

[Manufacturing method of electrolytic copper foil]
An example of the method for manufacturing the electrolytic copper foil of the present embodiment will be described below.
The electrolytic copper foil can be manufactured, for example, by using an electrolytic precipitation device as shown in FIGS. 1 and 2. The electrolytic precipitation apparatus of FIGS. 1 and 2 includes an insoluble electrode 12 made of titanium coated with a platinum group element or an oxide thereof, and a titanium rotating electrode 11 provided facing the insoluble electrode 12. There is.

Copper plating is performed using an electrolytic precipitation device, copper is deposited on the surface (columnar surface) of the columnar rotating electrode 11 to form a copper foil, and the copper foil is peeled off from the surface of the rotating electrode 11. Although the electrolytic copper foil of the present embodiment can be produced, the surface of the rotating electrode 11 is oxidized (hereinafter, may be referred to as “anode oxidation”) before copper plating, so that the surface of the rotating electrode 11 is more than a natural oxide film. An oxide film having a thick and uniform thickness may be formed.

Normally, a natural oxide film having a thickness of about several nm is formed on the surface of the rotating electrode 11, but the surface on which the natural oxide film is formed is further anodic oxidized to form an anodic oxide film. If an oxide film composed of a natural oxide film and an anode oxide film is formed, an oxide film thicker and more uniform than the natural oxide film is formed. If there is a distribution in the thickness of the oxide film, the resistance at the time of copper plating increases in the thick portion, and the plating amount decreases. As a result, the thickness of the electrolytic copper foil may be distributed, or pinholes may be generated in the electrolytic copper foil.

If an oxide film thicker than the natural oxide film and having a uniform thickness is formed by anodic oxidation, the distribution of foil thickness and pinholes can be suppressed. Further, due to the presence of the oxide film thicker than the natural oxide film, copper plating is performed at a higher overvoltage, so that the crystal grains of the initial precipitation layer of plating become fine. As a result, the elongation of the electrolytic copper foil after softening at room temperature is improved, the glossiness of the electrolytic precipitation end surface is improved, and the surface roughness is reduced. Therefore, it is possible to manufacture an electrolytic copper foil that is unlikely to break during expansion and contraction when used as a negative electrode current collector.

The thickness of the anodic oxide film formed by anodic oxidation is controlled by the amount of electricity applied to the rotating electrode 11 (unit is C / dm ² ), and more specifically, the amount of electricity per unit area of the surface of the rotating electrode 11. be able to. By controlling the thickness of the anodic oxide film, it is possible to control the thickness of the oxide film composed of the natural oxide film and the anodic oxide film.

The amount of electricity applied to the rotating electrode 11 is preferably 1000 C / dm ² or more and 5000 C / dm ² or less. Within the above numerical range, it becomes easy to control the parameter Gs / t to 10 or more and 40 or less. Further, within the above numerical range, it is possible to prevent the oxide film from becoming too thick, so that the surface roughness of the electrolytic copper foil becomes large due to abnormal precipitation in copper plating, etc., and the adhesion with the negative electrode material is increased. Can be suppressed from becoming non-uniform.

The method of manufacturing electrolytic copper foil by plating after anodic oxidation will be described below. First, anodic oxidation will be described with reference to FIG. When performing anode oxidation, a current is applied using the rotating electrode 11 as the anode and the insoluble electrode 12 as the cathode. As the insoluble electrode 12, for example, a DSE (Dimensionally Stable Electrode) electrode (registered trademark) can be used. Further, as the electrolytic solution 13, for example, a phosphoric acid aqueous solution having a concentration of 20% can be used.

While supplying the electrolytic solution 13 from the electrolytic solution supply unit (not shown) between the rotating electrode 11 and the insoluble electrode 12 (see the white arrow) and rotating the rotating electrode 11 in the direction indicated by the dotted arrow at a constant speed, A DC current is applied between the rotating electrode 11 and the insoluble electrode 12. Then, an anodic oxide film is formed on the natural oxide film on the surface of the rotating electrode 11, and an oxide film thicker and more uniform than the natural oxide film is formed.

Next, copper plating will be described with reference to FIG. When copper plating is performed, a current is applied using the rotating electrode 11 having an oxide film formed as a cathode and the insoluble electrode 12 as an anode. Further, as the electrolytic solution 13, for example, an aqueous solution containing sulfuric acid and copper sulfate can be used. The copper concentration of the electrolytic solution 13 can be, for example, 50 to 150 g / L, and the sulfuric acid concentration can be, for example, 20 to 200 g / L.

While supplying the electrolytic solution 13 from the electrolytic solution supply unit (not shown) between the rotating electrode 11 and the insoluble electrode 12 (see the white arrow) and rotating the rotating electrode 11 in the direction indicated by the dotted arrow at a constant speed, When a DC current is applied between the rotating electrode 11 and the insoluble electrode 12, copper is deposited on the surface of the rotating electrode 11. The electrolytic copper foil 14 is obtained by peeling the precipitated copper from the surface of the rotating electrode 11, pulling it up as shown by the solid arrow in FIG. 2, and continuously winding it.

Additives such as organic additives and inorganic additives may be added to the electrolytic solution 13 used for copper plating from the viewpoint of smoothing the electrolytic copper foil and controlling mechanical properties. By adding the additive, the strength, elongation, surface roughness, and glossiness under normal conditions can be improved. One type of additive may be used alone, or two or more types may be used in combination.

Examples of the organic additive include ethylenethiourea, polyethylene glycol, and Janus Green.
As the inorganic additive, for example, metal chloride such as sodium chloride (NaCl) or hydrogen chloride (HCl) can be used as a source of chloride ions.

It is preferable to add 10 to 50% by mass of chloride ion (chlorine) as an inorganic additive to the electrolytic solution 13 used for copper plating, and a total of at least one of ethylenethiourea, polyethylene glycol and Janus Green as an organic additive. It is preferable to add 3 to 30% by mass in ppm.
The electrolysis conditions for copper plating can be, for example, as follows. That is, the liquid temperature of the electrolytic solution 13 is 18 to 67 ° C., and the current density is 3 to 67 A / dm ² .

If desired, the surface of the electrolytic copper foil produced as described above may be surface-treated. The surface treatment will be described below.
The surface of the electrolytic copper foil may be subjected to a rust preventive treatment. Examples of the rust preventive treatment include an inorganic rust preventive treatment and an organic rust preventive treatment. Examples of the inorganic rust preventive treatment include chromate treatment and plating treatment, and chromate treatment may be applied to the plating layer by the plating treatment. Examples of the plating treatment include nickel plating, nickel alloy plating, cobalt plating, cobalt alloy plating, zinc plating, zinc alloy plating, tin plating, and tin alloy plating. Examples of the organic rust preventive treatment include surface treatment using benzotriazole.

The surface that has been subjected to the rust preventive treatment may be further subjected to surface treatment (silane treatment) using a silane coupling agent. By surface treatment using a silane coupling agent, a functional group having a strong affinity with an adhesive is imparted to the surface of the electrolytic copper foil (the surface on the bonding side with the negative electrode material or the resin), so that the electrolytic copper foil and the negative electrode material are provided. Adhesion with the resin and the resin is further improved, and the rust resistance and moisture absorption heat resistance of the electrolytic copper foil are further improved. Therefore, such an electrolytic copper foil is suitable as an electrolytic copper foil for a negative electrode current collector of a lithium ion secondary battery.
The rust preventive treatment and the silane coupling agent treatment increase the adhesion strength between the active material of the lithium ion secondary battery and the electrolytic copper foil, and play a role of preventing deterioration of the charge / discharge cycle characteristics of the lithium ion secondary battery.

Further, the surface of the electrolytic copper foil may be roughened before the above-mentioned rust preventive treatment is applied. As the roughening treatment, for example, a plating method, an etching method, or the like can be preferably adopted. The plating method is a method of roughening the surface by forming a thin film layer having irregularities on the surface of the untreated electrolytic copper foil. Examples of the plating method include an electrolytic plating method and an electroless plating method.

As the roughening treatment by the plating method, for example, a method of forming a plating film containing copper as a main component such as copper or a copper alloy on the surface of an untreated electrolytic copper foil is preferable. As the roughening treatment by the etching method, for example, a method by physical etching or chemical etching is preferable. Examples of the physical etching include a method of etching by sandblasting and the like, and examples of the chemical etching include etching performed by using a treatment liquid containing an inorganic acid or an organic acid, an oxidizing agent and an additive.

〔Example〕
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. The electrolytic copper foils of Examples 1 to 27 and Comparative Examples 1 to 13 are manufactured, negative electrode current collectors are manufactured using these electrolytic copper foils, and a lithium ion secondary battery is manufactured using these negative electrode current collectors. Was manufactured respectively. Then, various characteristics of the electrolytic copper foil and the lithium ion secondary battery were evaluated. A method for manufacturing an electrolytic copper foil and a lithium ion secondary battery and a method for evaluating various characteristics will be described.

(A) Anode oxidation An anodic oxidation was performed by the same operation as described above using the same equipment as in FIG. 1, and an oxide film was formed on the surface of the rotating electrode. An aqueous phosphoric acid solution having a concentration of 20% was used as the electrolytic solution. The thickness of the oxide film was controlled by the amount of electricity applied to the rotating electrode. Table 1 shows the amount of electricity applied to the rotating electrode. Comparative Examples 8 to 10 are examples in which anodic oxidation was not performed.

(B) Copper plating Following the anodic oxidation in item (A) above, copper plating was performed in the same manner as described above to deposit copper on the surface of the rotating electrode on which the oxide film was formed. Then, the precipitated copper was peeled off from the surface of the rotating electrode and continuously wound to produce electrolytic copper foils of Examples and Comparative Examples (see FIG. 2). The temperature and current density of the electrolytic solution at the time of copper plating are as shown in Table 1.

An aqueous solution containing sulfuric acid, copper sulfate pentahydrate, and additives was used as the electrolytic solution. As additives, ethylene thiourea, polyethylene glycol, and Janus Green were used. Table 1 shows the concentrations of sulfuric acid, copper sulfate pentahydrate, and each additive. The concentration of copper sulfate pentahydrate is the concentration as copper. Table 1 shows the chlorine concentration in the electrolytic solution.

(C) Chromate treatment The surface of each electrolytic copper foil produced in the above item (B) was subjected to chromate treatment to form a rust preventive treatment layer, which was used as a negative electrode current collector. The conditions for chromate treatment are as follows. The plating solution used for the chromate treatment contains potassium dichromate, the chromium concentration is preferably in the range of 6 to 12 g / L, and the treatment time of the chromate treatment is in the range of 8 to 12 seconds. Is desirable. In this example and the comparative example, the chromium concentration was 10 g / L, and the chromate treatment treatment time was 10 seconds.

(D) Production of positive electrode N-methyl-2-pyrrolidone and ethanol are added as solvents to a mixture of 90% by mass of lithium cobalt oxide (LiCoO ₂ ) powder, 7% by mass of graphite powder, and 3% by mass of polyvinylidene fluoride powder. The positive electrode material paste was prepared by kneading. This positive electrode material paste was uniformly applied onto the aluminum foil with a thickness of 15 μm. The aluminum foil coated with the positive electrode material paste was dried in a nitrogen atmosphere to volatilize the solvent, and then roll-rolled to prepare a sheet having an overall thickness of 150 μm. After cutting this sheet into a strip having a width of 43 mm and a length of 285 mm, a lead terminal of aluminum foil was attached to one end thereof by ultrasonic welding to obtain a positive electrode.

(E) Production of Negative Electrode N-methyl-2-pyrrolidone and ethanol are added and kneaded as a solvent to a mixture of 90% by mass of natural graphite powder having an average particle size of 10 μm and 10% by mass of polyvinylidene fluoride powder, and the negative electrode is used. A material paste was prepared.

Each negative electrode current collector manufactured in the above item (C) was cut into a strip having a width of 720 mm. At this time, the width direction of the electrolytic copper foil was made to coincide with the width direction of the strip obtained by cutting. Next, the negative electrode material paste was applied to both sides of the strip in a double stripe shape. The width of the coating film of the linear negative electrode material paste was 300 mm, and the direction in which the coating film of the linear negative electrode material paste was stretched was made parallel to the longitudinal direction of the strip.

The strip coated with the negative electrode material paste was dried in a nitrogen atmosphere to volatilize the solvent, and then roll-rolled to prepare a sheet having an overall thickness of 150 μm. After cutting this sheet into a rectangular shape having a width of 43 mm and a length of 280 mm, a nickel foil lead terminal was attached to one end thereof by ultrasonic welding to form a negative electrode.

(F) Preparation of Lithium Ion Secondary Battery A polypropylene separator having a thickness of 25 μm was sandwiched between the positive electrode and the negative electrode manufactured as described above, and all of them were wound to obtain a wound body. The wound body was housed in a cylindrical battery can, and the lead terminal of the negative electrode was spot welded to the bottom of the battery can. The battery can is made of mild steel whose surface is nickel-plated.

Next, the top lid made of insulating material was placed on the battery can, and after inserting the gasket, the lead terminal of the positive electrode and the safety valve made of aluminum were ultrasonically welded and connected. Then, after injecting a non-aqueous electrolyte solution consisting of propylene carbonate, diethyl carbonate, and ethylene carbonate into the battery can, a lid is attached to the safety valve, and a cylindrical sealed structure lithium ion battery with an outer diameter of 14 mm and a height of 50 mm is attached. I assembled the next battery.

Next, various characteristics of each electrolytic copper foil manufactured in the above item (B) and each lithium ion secondary battery manufactured in the above item (F) were evaluated. The evaluation method will be described below. The foil thickness of each electrolytic copper foil produced in the above item (B) is as shown in Table 2.

[Glossiness Gs of electrolytic copper foil]
Using a gloss meter VG7000 manufactured by Nippon Denshoku Industries Co., Ltd., the glossiness of the electrolytic precipitation end surface of the electrolytic copper foil was measured based on the method specified in JIS Z8741-1997. In the measurement of the glossiness, the glossiness was measured by irradiating the electrolytic precipitation end surface with light at an incident angle of 60 ° along the length direction (MD) of the electrolytic copper foil. The glossiness was measured 5 times, and the average value of these was taken as the glossiness Gs. The results are shown in Table 2.
The glossiness was measured by using a normal electrolytic copper foil as a measurement target. In the present invention, the "normal state" means a state in which the electrolytic copper foil is placed at room temperature and humidity (for example, temperature 23 ± 2 ° C., humidity 50 ± 5% RH).

[Elongation E and tensile strength of electrolytic copper foil]
A normal electrolytic copper foil that had not been heat-treated was cut into a rectangular shape having a width of 12.7 mm and a length of 130 mm, and this was used as a measurement sample. Then, a tensile tester 1122 manufactured by Instron was used to perform a tensile test on the measurement sample based on the method specified in IPC-TM-650, and the elongation at break and the tensile strength were measured. In this tensile test, the distance between chucks was 70 mm and the tensile speed was 50 mm / min. Tensile tests were performed on five measurement samples, and the average values of these were taken as elongation E and tensile strength. The results are shown in Table 2.

[Root mean square height Sq of electrolytic copper foil]
With reference to ISO25178, the surface shape of the electrolytic precipitation end surface of the electrolytic copper foil was measured using a white light interference type optical microscope WykoContourGT-K manufactured by BRUKER, with the normal electrolytic copper foil as the measurement target. The analysis was performed to obtain the root mean square height Sq. The surface shape was measured at any 5 points on the end surface of electrolytic precipitation, and shape analysis was performed at each of the 5 points to obtain the root mean square height Sq at each of the 5 points. Then, the average value of the results of the obtained five points was taken as the root mean square height Sq of the electrolytic precipitation end surface of the electrolytic copper foil.

The shape analysis was performed by the VSI measurement method (vertical scanning interferometry) using a high resolution CCD camera. The conditions were that the light source was white light, the resolution was 1280 × 980 pixels, the measurement magnification was 10 times, the measurement range was 477 μm × 357.8 μm, and Threshold was 3%. Further, the entire measurement range of 477 μm × 357.8 μm was filtered by Terms Removal (Cylinder and Tilt) and Data Ristorante (Measode: legacy, iterations 5), and then Fourier Filter processing was performed.

For the Fourier Filter treatment, High Freq Pass was used as the Fourier filtering, Gaussian was used as the Fourier Filter Window, and the High Frequency was set to 12.5 mm ^-1 in the Frequency Cutoff.
Further, a Statistic Filter (Statistic Size: 3, Filter Type: Median) treatment was performed.
The root mean square height Sq was calculated by using S-parameters-height analysis with Remove Til as True. The results are shown in Table 2.

[Evaluation of charge / discharge cycle characteristics of lithium-ion secondary batteries]
A charge / discharge cycle test was conducted in which a lithium ion secondary battery was charged to 4.2 V at a charge current of 100 mA and then discharged to 2.4 V at a discharge current of 100 mA as one cycle. After repeating this cycle, the lithium ion secondary battery was disassembled and the presence or absence of breakage of the electrolytic copper foil was examined. The results are shown in Table 2.

In Table 2, when no break is observed even after 500 cycles, it is indicated by "A", when it is broken in 300 cycles or more and less than 500 cycles, it is indicated by "B", and when it is broken in less than 300 cycles, it is indicated by "C". be.
It can be said that an electrolytic copper foil that breaks in less than 300 cycles is not suitable for use as a negative electrode current collector. It can be said that the electrolytic copper foil that breaks in 300 cycles or more and less than 500 cycles is suitable for the use of a negative electrode current collector. The electrolytic copper foil that does not break even after 500 cycles is particularly suitable for the use of the negative electrode current collector, and can improve the charge / discharge cycle characteristics of the lithium ion secondary battery.

As can be seen from Table 2, in the lithium ion secondary batteries using the electrolytic copper foils of Examples 1 to 27 as the negative electrode current collector, the foil thickness t of the electrolytic copper foil is 10 or more and 20 or less, and Gs / t is high. Since it is 10 or more and 40 or less and the E / t is 0.9 or more and 1.8 or less, the electrolytic copper foil is less likely to break even after repeated charging and discharging, and the charge and discharge cycle characteristics of the lithium ion secondary battery are excellent. Was there.

11 ... Rotating electrode 12 ... Insoluble electrode 13 ... Electrolyte solution 14 ... Electrolyzed copper foil

Claims (9)

1. The foil thickness is t (unit: μm), and the glossiness of the electrolytic precipitation end surface measured by irradiating the electrolytic precipitation end surface with light at an incident angle of 60 ° along the length direction is Gs (unit is). %), When the elongation measured by pulling along the length direction is E (unit is%), the foil thickness t is 10 or more and 20 or less, and Gs / t obtained by dividing the glossiness Gs by the foil thickness t is An electrolytic copper foil having an E / t of 10 or more and 40 or less and an elongation E divided by a foil thickness t of 0.9 or more and 1.8 or less.
2. The foil thickness t is 12 or more and 20 or less, the Gs / t obtained by dividing the glossiness Gs by the foil thickness t is 25 or more and 40 or less, and the E / t obtained by dividing the elongation E by the foil thickness t is 1.2 or more and 1 .. The electrolytic copper foil according to claim 1, which is 7 or less.
3. The electrolytic copper foil according to claim 1 or 2, wherein E / t obtained by dividing the elongation E by the foil thickness t is 1.3 or more and 1.6 or less.
4. The electrolytic copper foil according to any one of claims 1 to 3, wherein the root mean square height Sq of the electrolytic precipitation end surface measured using a white interference microscope is 0.1 μm or more and 0.4 μm or less.
5. The electrolytic copper foil according to any one of claims 1 to 3, wherein the root mean square height Sq of the electrolytic precipitation end surface measured using a white interference microscope is 0.1 μm or more and 0.25 μm or less.
6. The electrolytic copper foil according to any one of claims 1 to 5, wherein the tensile strength measured by pulling along the length direction is 300 MPa or more and 380 MPa or less.
7. The electrolytic copper foil according to any one of claims 1 to 6, which is for a negative electrode current collector of a lithium ion secondary battery.
8. A negative electrode for a lithium ion secondary battery provided with the electrolytic copper foil according to any one of claims 1 to 7.
9. A lithium ion secondary battery comprising the negative electrode for the lithium ion secondary battery according to claim 8.

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