TW202223163A - Electrolytic copper foil, negative electrode for lithium ion secondary cell, and lithium ion secondary cell - Google Patents

Abstract

The present invention provides an electrolytic copper foil which is not susceptible to breaking. In this electrolytic copper foil, where t is the foil thickness (in units of [mu]m), VAV is the recess average volume (in units of [mu]m3), which is the average value of the volume of recesses formed in an electrolytic-deposition-completed surface, E is the elongation (in units of %) measured by pulling along a length direction, and the recess average volume VAV is measured using a white interference microscope, the foil thickness t is 10 to 20[mu]m, the product VAV*t of the recess average volume VAV and the foil thickness t is more than 0[mu]m4 and no more than 1000[mu]m4, and the quotient E/t of the elongation E divided by the foil thickness t is 0.9%/[mu]m to 1.8%/[mu]m.

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 a lithium ion secondary battery.

As the negative electrode current collector of the lithium ion secondary battery, copper foil is sometimes used, and the copper foil may be broken due to expansion and contraction of the negative electrode material during charge and discharge of the lithium ion secondary battery. In addition, the adhered copper foil and the negative electrode material are partially peeled off during charge and discharge, and since the stress during expansion and contraction is concentrated on the peeled portion, the copper foil may be broken. Patent Documents 1 and 2 disclose an electrolytic copper foil which can be used as a negative electrode current collector of a lithium ion secondary battery, and which improves adhesion to a negative electrode material by controlling the surface roughness. Patent Document 3 discloses an electrolytic copper foil for a secondary battery excellent in flexibility, which can withstand expansion and contraction of a negative electrode material during charge and discharge. Patent Document 4 discloses a technique for producing a secondary battery having excellent performance using a copper foil whose slack, wrinkles, and tearing have been controlled by controlling surface roughness and the like. In recent years, research on lithium ion secondary batteries has continued, and further improvement in performance has been demanded. Therefore, there has been demand for a copper foil that is more difficult to break during charge and discharge. The electrolytic copper foils disclosed in Patent Documents 1 to 4 have insufficient mechanical properties and adhesion to the negative electrode material, and therefore may be broken during charging and discharging of the lithium ion secondary battery.

[Prior Art Literature] (patent literature) Patent Document 1: Japanese Patent Publication No. 6587701 Patent Document 2: International Publication No. 2018/207786 Patent Document 3: Japanese Patent Laid-Open Publication No. 502728 of 2020 Patent Document 4: Japanese Patent Laid-Open Publication No. 26563 of 2020

[Problems to be Solved by Invention] The problem to be solved by the present invention is to provide an electrolytic copper foil that is difficult to break. In addition, the problem to be solved by 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 be broken during charge and discharge.

[MEANS TO SOLVE THE PROBLEM] Regarding the electrolytic copper foil of one aspect of the present invention, the gist is: when the foil thickness is t (μm), the volume of the concave portion to be formed on the electrolytic desorption end surface is The average value, that is, the average volume of the concave portion is set to VAV (μm ³ ), the elongation rate measured by stretching in the longitudinal direction is set to E (%), and the average volume of the concave portion VAV is measured using a white light interference microscope, When the foil thickness t is 10 μm or more and 20 μm or less, the product of the average volume VAV of the concave portion and the foil thickness t, that is, VAV×t is more than 0 μm ⁴ and 1000 μm ⁴ or less, E/t obtained by dividing the elongation E by the foil thickness t It is 0.9%/μm or more and 1.8%/μm or less.

Moreover, about the negative electrode for lithium ion secondary batteries of another aspect of this invention, the summary is provided with the electrolytic copper foil of the said aspect. Furthermore, about the lithium ion secondary battery of another aspect of this invention, the gist is provided with the negative electrode for lithium ion secondary batteries of the said other aspect.

[effect] The electrolytic copper foil of the present invention is hardly broken. In addition, in the negative electrode for a lithium ion secondary battery and the lithium ion secondary battery of the present invention, the negative electrode current collector is less likely to be broken during charge and discharge.

An embodiment of the present invention will be described. In addition, the embodiment described below is an example which shows this invention. In addition, various changes or improvements can be made to the present embodiment, and such changes or improvements are also included in the present invention. Regarding the electrolytic copper foil of one embodiment of the present invention, when the foil thickness is t (unit is μm), the average value of the volume of the recesses to be formed on the electrolytic desorption end surface is the average volume of the recesses (Valleys Average). When the mean volume VAV of the concave portion is measured using a white light interference microscope, the thickness ^of the foil is t is 10 μm or more and 20 μm or less, the product of the average volume VAV of the concave portion and the foil thickness t, that is, VAV×t is more than 0 μm ⁴ and 1000 μm ⁴ or less, and E/t obtained by dividing the elongation E by the foil thickness t is 0.9 %/μm or more and 1.8%/μm or less. With such a structure, the electrolytic copper foil of the present embodiment is less likely to be broken.

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 lithium ion secondary batteries of this embodiment is equipped with the electrolytic copper foil of this embodiment. Moreover, the lithium ion secondary battery of this embodiment is equipped with the negative electrode for lithium ion secondary batteries of this embodiment. Since the electrolytic copper foil of the present embodiment is difficult to break, the negative electrode for a lithium ion secondary battery and the lithium ion secondary battery of the present embodiment are less likely to break the negative electrode current collector during charge and discharge.

Hereinafter, the electrolytic copper foil of the present embodiment will be described in further detail. The inventors of the present invention, as a result of intensive examination, found the fact that an electrolytic copper foil having both characteristics of high elongation and smoothness (low profile) of the electrolytically decomposed finish surface can be used during charging and discharging of lithium ion secondary batteries. , even if the negative electrode material expands and contracts, it is difficult to break.

When the electrolytic copper foil has high stretchability, the electrolytic copper foil can follow the expansion and contraction of the negative electrode material, and thus it is difficult to break. In addition, if the average value of the volume of the fine concave portions formed on the electrodeposition finish surface, that is, the concave portion average volume VAV is small, and the electrodeposition finish surface is smooth, the adhesion force between the electrodeposited copper foil and the negative electrode material will be reduced due to the adhesion. Since it becomes uniform over the entire adhesion surface, the occurrence of local peeling during charge and discharge is suppressed between the adhered electrodeposited copper foil and the negative electrode material. If local peeling occurs between the electrolytic copper foil and the negative electrode material, the stress during expansion and contraction is concentrated on the peeled part, so the electrolytic copper foil is easily broken, but the electrolytic copper foil of this embodiment is less likely to locally occur Therefore, it is difficult to break during the charging and discharging of the lithium ion secondary battery. This point will be described in further detail below.

In the past, the relationship between the foil thickness t of the electrolytic copper foil and the elongation rate due to stretching has many uncertainties, and even electrolytic copper foils with the same foil thickness have variations in the properties such as elongation rate. In addition, if the thickness of the foil is increased, the deposition mechanism of copper in the electrolytic plating (copper plating for producing the electrolytic copper foil) changes, and the electrolytic copper foil may also be damaged during charging and discharging of the lithium ion secondary battery. Problems such as premature breakage.

As a result of intensive examination, the present inventors found that by controlling the electrolytic conditions of electrolytic plating, the value obtained by normalizing the elongation ratio to the foil thickness (that is, the parameter E/t) falls within a predetermined range. Moreover, in the lithium ion secondary battery manufactured using the electrolytic copper foil obtained in this way as a negative electrode current collector, the negative electrode current collector is less likely to be broken during charge and discharge.

Moreover, conventionally, it was thought that a smooth electrolytic copper foil with a smaller surface roughness such as Ra and Rz is less likely to be broken. However, since the surface roughness of Ra, Rz, etc. is calculated from the contour on any line in the surface of the electrolytic copper foil, the fine recesses existing in the region having a certain area are not sufficiently expressed. size, etc.

As a result of intensive examination, the present inventors found that copper crystals grow in the thickness direction of the electrolytic copper foil during electrolytic plating, so that many fine recesses on the order of cubic micrometers are formed on the surface of the electrolytic copper foil. When the volume of the concave portion is large, when the negative electrode material expands and contracts during charging and discharging of the lithium ion secondary battery, the concave portion becomes a starting point, and the electrolytic copper foil is likely to be broken. The concave portion formed by this copper crystal growth may become larger in proportion to the thickness of the foil.

The present inventors have found the fact that by controlling the conditions of electrolytic plating, if the average value of the volumes of the concave portions formed on the electro-deposited finish surface, that is, the concave portion average volume VAV, is made small and the effect due to the thickness of the foil is controlled The effect on the average volume VAV of the concave portion is not high, and an electrolytic copper foil with high elongation ratio and difficult to break can be obtained.

FIG. 2 is a white light interference photomicrograph showing the unevenness formed on the electrolytic desorption end surface of the electrolytic copper foil, and the height is indicated by the shade of color. FIG. 3 is a diagram showing the outline of the electrolytic desorption end surface of the electrolytic copper foil, and shows the outline of one line in the white light interference micrograph of FIG. 2 . The portion lower than the horizontal line with a height of 0 μm set on the basis of the international standard ISO25178 is a concave portion formed on the end surface of the electrolytic desorption.

The concave portion average volume VAV is influenced by the following two factors: inhibition of copper growth in the thickness direction of the electrolytic copper foil and increase in the thickness of the foil. Therefore, for electrolytic copper foils with different foil thicknesses, when the above-mentioned degree of suppression of crystal growth is derived from the average volume VAV of the recesses, it is necessary to compare the product of the average volume VAV of the recesses and the foil thickness t, that is, VAV×t. As described above, by specifying both the parameter VAV×t and the parameter E/t, an electrolytic copper foil for which breakage is unlikely to occur can be obtained.

[foil thickness t] The foil thickness t must be 10 μm or more and 20 μm or less, preferably 12 μm or more and 20 μm or less. When the foil thickness t is within the above-mentioned range, the organic additive in the electrolytic solution functions to fill the large irregularities of the electro-deposited copper foil due to the growth in the thickness direction, so that it is possible to suppress the thickness direction of the electro-deposited copper foil. The effect of crystal growth. As a result, it is possible to obtain an electrolytic copper foil in which the average value of the volume of the concave portions formed on the electrolytic desorption finished surface, that is, the concave portion average volume VAV, is reduced, has a high elongation ratio, and is less likely to occur. break.

When starting to energize the cathode, that is, in the area of the foil thickness t from 0 μm to less than 10 μm, the crystal growth in the thickness direction of the electrolytic copper foil takes priority, the average volume VAV of the concave part tends to increase, and the tensile fracture is premature. Chances are higher. In the area where the foil thickness t exceeds 20 μm, since the electrolysis time required for foil production becomes longer, it is easily affected by the decomposition and consumption of organic additives, and the average volume VAV of the concave portion becomes significantly larger. As a result, the occurrence of There is a high possibility that the local elongation rate decreases.

[VAV×t] The parameter VAV×t must be more than 0 μm ⁴ and 1000 μm ⁴ or less, preferably more than 0 μm ⁴ and 400 μm ⁴ or less. When the parameter VAV×t is within the above range, since the surface of the electrolytic copper foil is smooth, the adhesion force between the electrolytic copper foil and the negative electrode material tends to be uniform over the entire adhesion surface. Therefore, local peeling during charge and discharge is suppressed between the closely-contacted electrolytic copper foil and the negative electrode material, and breakage during charge and discharge is less likely to occur. On the other hand, when the parameter VAV×t is within the above-mentioned range, since the adhesive force between the electrolytic copper foil and the negative electrode material is sufficiently exhibited, breakage is unlikely to occur during charge and discharge.

[E/t] The parameter E/t must be 0.9%/μm or more and 1.8%/μm or less, preferably 1.2%/μm or more and 1.7%/μm or less, more preferably 1.3%/μm or more and 1.6%/μm or less. If the parameter E/t is within the above-mentioned range, since the electrolytic copper foil has a high elongation ratio, it is difficult to break during charging and discharging.

[Root mean square height Sq] The root mean square height Sq of the electrolytic copper foil of the present embodiment measured using a white light interference microscope is preferably 0.1 μm or more and 0.4 μm or less, and more preferably 0.1 μm or more and 0.25 μm or less.

If the root-mean-square height Sq of the electrodeposition end surface is within the above-mentioned range, the adhesion between the electrolytic copper foil and the negative electrode material is more likely to be increased by the anchoring effect. In addition, when the root mean square height Sq of the electro-deposition end surface is within the above-mentioned range, since the electro-deposition end surface is sufficiently smooth, the adhesion force between the adhered electrolytic copper foil and the negative electrode material becomes uniform over the entire adherence surface. . Thereby, the occurrence of local peeling during charge and discharge is suppressed between the closely-contacted electrolytic copper foil and the negative electrode material, so that breakage during charge and discharge is less likely to occur.

[Tensile Strength] The electrolytic copper foil of the present embodiment has a tensile strength of 300 MPa or more and 380 MPa or less measured by being stretched in the longitudinal direction. When the tensile strength is within the above range, the electrolytic copper foil is more difficult to be broken, and the followability to the expansion and contraction of the negative electrode material is also more excellent.

The tensile strength of the electro-deposited copper foil is measured by stretching along the longitudinal direction. The "longitudinal direction" of the electro-deposited copper foil in the present invention means MD (Machine Direction). For example, in the electro-deposited copper foil At the time of manufacture, when a rotating electrode is used and the surface of the rotating electrode is plated to form a copper foil, it means the rotation direction of the rotating electrode.

In addition, the electrolytic copper foil of this embodiment can be used not only for the negative electrode current collector of a lithium ion secondary battery, but also for other applications. For example, the electrolytic copper foil of the present embodiment can be suitably used as a copper foil for a printed wiring board. Since the electrodeposited copper foil of the present embodiment has both high elongation and smoothness of the electrolytically decomposed surface, even if the electrodeposited copper foil is bonded to the copper foil during the manufacture of printed wiring boards (for example, during hot pressing) When resin, such as an epoxy resin, expands and contracts, since copper foil follows this expansion and contraction, it is hard to break.

[Manufacturing method of electrolytic copper foil] An example of the manufacturing method of the electrolytic copper foil of this embodiment is demonstrated below. The electrolytic copper foil can be produced using, for example, the electrolytic separation apparatus shown in FIG. 1 . The electro-desorption apparatus of FIG. 1 includes an insoluble electrode 12 made of titanium covered with a platinum group element or its oxide, and a titanium rotating electrode 11 provided to face the insoluble electrode 12 . Copper plating is performed using the electrolytic precipitation apparatus shown in FIG. 1, copper is deposited on the surface (cylindrical surface) of the cylindrical rotating electrode 11 to form a copper foil, and then the copper foil is peeled off from the surface of the rotating electrode 11, whereby it is possible to The electrolytic copper foil of this embodiment was manufactured.

In addition, by controlling the current density, the temperature of the electrolyte, the composition of the electrolyte (for example, the concentration of copper ions, sulfuric acid, chloride ions, additives in the electrolyte) and other conditions during copper plating, the thickness of the electrolytic copper foil can be suppressed. direction of copper crystal growth. As a result, it is possible to obtain an electro-deposited copper foil having a small concave portion average volume VAV, a small change in surface properties (eg, concave portion average volume VAV, root-mean-square height Sq) due to the foil thickness of the electrolytic copper foil, and high elongation. Rate.

An example of the method of performing copper plating to manufacture an electrolytic copper foil will be described in detail with reference to FIG. 1 . When copper plating is performed, a current is applied with the rotating electrode 11 serving as a cathode and the insoluble electrode 12 serving as an anode. As the insoluble electrode 12 , for example, a DSE electrode (coated titanium electrode, Dimensionally Stable Electrode) (registered trademark) can be used. In addition, as the electrolytic solution 13, for example, an aqueous solution containing sulfuric acid and copper sulfate can be used. The copper concentration of the electrolyte solution 13 can be, for example, 50 to 150 g (grams)/L (liters), and the sulfuric acid concentration can be 20 to 200 g/L.

The electrolyte solution 13 is supplied between the rotating electrode 11 and the insoluble electrode 12 (refer to the white arrow) from the electrolyte solution supply unit (not shown), and the rotating electrode 11 is moved at a predetermined speed in the direction indicated by the broken line arrow. While rotating and applying a direct current 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 can be obtained by peeling the deposited copper from the surface of the rotating electrode 11 , pulling up as indicated by the solid arrow in FIG. 1 and continuously winding.

In the electrolytic solution 13 for copper plating, additives such as organic additives and inorganic additives may be added from the viewpoint of smoothing of the electrolytic copper foil and control of mechanical properties. By adding an additive, the strength, elongation, and surface roughness of the electrolytic copper foil in a normal state can be improved, or the crystal growth of copper in copper plating can be suppressed. An additive may be used individually by 1 type, and may be used in combination of 2 or more types.

Examples of organic additives include ethylene thiourea, polyethylene glycol, and Janus green. As the inorganic additive, for example, metal chlorides such as sodium chloride (NaCl), which are sources of chloride ions, or hydrogen chloride (HCl) can be used.

In the electrolytic solution 13 for copper plating, it is preferable to add 20 to 50 mg/L of chloride ions (chlorine) as an inorganic additive. In addition, in the electrolytic solution 13 for copper plating, as the organic additive, at least one of ethylene thiourea, polyethylene glycol, and kena green is preferably added in a total amount of 3 to 30 mg/L It is added, and it is more preferable to add it in a total amount of 3 to 10 mg/L.

During copper plating, copper crystals may grow in the thickness direction of the electrolytic copper foil, but if at least one of ethylene thiourea, polyethylene glycol, and kena green is added to the electrolyte at a concentration within the above range In 13, the effect of suppressing the crystal growth of copper in the thickness direction of the electrolytic copper foil becomes large.

The electrolytic conditions in copper plating can be, for example, the following conditions. That is, the liquid temperature of the electrolyte solution 13 is 45 to 65° C., and the current density is 25 to 50 A/dm ² . During copper plating, the temperature of the electrolyte 13 rises due to resistance heating of the anode and the cathode, and the organic additives may be decomposed. Therefore, it is preferable to suppress the current density to the above-mentioned low value.

The surface of the electrolytic copper foil produced as described above may be surface-treated as desired. The surface treatment is explained below. Antirust treatment can also be applied to the surface of the electrolytic copper foil. Examples of the antirust treatment include inorganic and organic antirust treatments. As an inorganic rust-proofing process, a chromate process and a plating process are mentioned, for example, You may give a chromate process to the plating layer formed by this plating process. 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. As an organic rust preventive treatment, the surface treatment using benzotriazole is mentioned, for example.

For the surface that has been subjected to anti-rust treatment, surface treatment (silane modification treatment) using a silane coupling agent can also be further carried out. By surface treatment using a silane coupling agent, the surface of the electrolytic copper foil (the surface on the bonding side with the negative electrode material or resin, etc.) is given a functional group with a strong affinity for the adhesive, so the electrolytic copper foil is Adhesion of the negative electrode material, resin, etc. is further improved, and the rust resistance, moisture absorption heat resistance, etc. of the electrolytic copper foil are further improved. Therefore, such an electrolytic copper foil is suitable as an electrolytic copper foil for negative electrode current collectors of lithium ion secondary batteries or for printed wiring boards. Anti-rust treatment and surface treatment using silane coupling agent improve the adhesion strength between the active material of the lithium ion secondary battery and the electrolytic copper foil, and achieve the effect of preventing the deterioration of the charge-discharge cycle characteristics of the lithium ion secondary battery.

Moreover, you may perform roughening process on the surface of an electrolytic copper foil before performing the said rust-proof process. As a roughening process, a plating method, an etching method, etc. can be suitably used, for example. The plating method is a method of roughening the surface by forming a thin film layer having irregularities on the surface of an untreated electrolytic copper foil. As a plating method, an electrolytic plating method and an electroless plating method are mentioned.

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 a roughening process performed by an etching method, the method performed by physical etching, chemical etching, etc. is preferable, for example. Examples of physical etching include a method of etching by sandblasting or the like, and examples of chemical etching include etching using a treatment liquid containing an inorganic acid or an organic acid, an oxidizing agent, and an additive.

[Example] Hereinafter, an Example and a comparative example are shown, and this invention is demonstrated more concretely. First, the electrolytic copper foils of Examples 1 to 19 and Comparative Examples 1 and 2 were produced, and then negative electrode current collectors were produced using these electrodeposited copper foils, respectively, and lithium ion secondary batteries were produced using these negative electrode current collectors, respectively. Then, various properties of the electrolytic copper foil and the lithium ion secondary battery were evaluated. A method for producing an electrolytic copper foil and a lithium ion secondary battery and an evaluation method for various properties will be described.

(A) Copper plating Using the same apparatus as in Fig. 1, copper plating was performed by the same operation as described above, and copper was deposited on the surface of the rotating electrode. Then, the deposited copper was peeled off from the surface of the rotating electrode, and the electrolytic copper foils of Examples and Comparative Examples were produced by continuous winding (see FIG. 1 ). The temperature and current density of the electrolyte during copper plating are shown in Table 1.

As the electrolyte, an aqueous solution containing sulfuric acid, copper sulfate pentahydrate and additives was used. As additives, ethylene thiourea, polyethylene glycol, and kena 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 of copper. In addition, Table 1 shows the chlorine concentration in the electrolyte solution.

[Table 1]

(B) Production of Positive Electrode N-methylpyrrolidone and ethanol were added to a mixture of 90% by mass of lithium cobaltate (LiCoO ₂ ), 7% by mass of graphite powder, and 3% by mass of polyvinylidene fluoride powder. The solvent is mixed and kneaded to prepare a positive electrode material paste. This positive electrode material paste was uniformly coated on the aluminum foil so as to have a thickness of 15 μm. After drying the aluminum foil coated with the positive electrode material paste in a nitrogen atmosphere to volatilize the solvent, rolling was performed to produce a sheet having a total thickness of 150 μm. This sheet was cut into a strip having a width of 43 mm and a length of 285 mm, and then a lead terminal of an aluminum foil was attached to one end by ultrasonic welding to prepare a positive electrode.

(C) Manufacture of negative electrode A negative electrode material paste was prepared by adding N-methylpyrrolidone and ethanol as a solvent to a mixture of 90 mass % of natural graphite powder having an average particle diameter of 10 μm and 10 mass % of polyvinylidene fluoride powder. Each of the electrolytic copper foils produced in the above (A) was cut into a strip having a width of 720 mm to prepare a negative electrode current collector. At this time, the width direction of the electrolytic copper foil was set to coincide with the width direction of the strip-shaped negative electrode current collector obtained by cutting.

Next, the negative electrode material paste was coated on both sides of the negative electrode current collector in a double-layered stripe shape. The width of the coating film of the linear negative electrode material paste was 300 mm, and the extension direction of the coating film of the linear negative electrode material paste was set to coincide with the longitudinal direction of the strip-shaped negative electrode current collector. After the negative electrode current collector coated with the negative electrode material paste was dried in a nitrogen atmosphere to volatilize the solvent, rolling was performed to produce a sheet having an overall thickness of 150 μm. This sheet was cut into a rectangular shape with a width of 43 mm and a length of 280 mm, and then a lead terminal of a nickel foil was attached to one end by ultrasonic welding to prepare a negative electrode.

(D) Fabrication of lithium ion secondary battery Between the positive electrode and the negative electrode produced as described above, a separator made of polypropylene with a thickness of 25 μm was sandwiched, and the entirety was wound to obtain a wound body. This wound body was accommodated in a cylindrical battery can, and the lead terminal of the negative electrode was spot welded to the bottom of the battery can. Furthermore, the battery can is formed of mild steel with nickel plating applied to the surface.

Next, the top cover made of insulating material was placed on the battery can, and after inserting the gasket, the lead terminal of the positive electrode and the aluminum safety valve were ultrasonically welded and joined. And, after injecting the non-aqueous electrolytic liquid consisting of acrylic carbonate, diethyl carbonate and ethylene carbonate into the battery can, the upper cover is mounted on the safety valve, and assembled into a cylindrical shape with an outer diameter of 14 mm and a height of 50 mm. Sealed structure type lithium ion secondary battery.

Next, various characteristics of each of the electrolytic copper foils produced in the above item (A) and each of the lithium ion secondary batteries produced in the above item (D) were evaluated. The evaluation method will be described below. In addition, the foil thickness of each electrolytic copper foil manufactured in the said item (A) is as described in Table 2.

[Table 2]

[Average volume VAV and root mean square height Sq of the concave portion at the end surface of electrolytic copper foil electrolytic desorption] The method for measuring the average volume VAV of the recessed portion and the root mean square height Sq described above is a method set with reference to the contents described in the international standard ISO25178. Using a white light interference type microscope Wyko ContourGT-K manufactured by Bruker, the surface shape of the electrolytically resolved surface of the electrolytic copper foil was measured, and shape analysis was performed to obtain the average volume VAV and root mean square height Sq of the concave portion. The measurement of the surface shape was carried out at any five places on the end surface of the electrolysis, and the shape analysis of each of the five places was carried out, and the average volume VAV of the concave portion and the root mean square height Sq of each of the five places were obtained. Then, the average value of the obtained results at five places was used as the average volume VAV of the concave portion and the root-mean-square height Sq of the electrolytic-deposited end surface of the electrolytic copper foil.

The shape analysis was performed by the VSI measurement method (vertical scanning type interferometry) using a high-resolution CCD camera (resolution 1280×960 pixels). The conditions are set as the light source is white light, the measurement magnification is 10 times, the measurement range is 477 μm × 357.8 μm, and the threshold value is 3%. , the implementation of Fourier filter processing.

In the Fourier filtering process, a high frequency band-pass filter (High Freq Pass) is used as the Fourier filter, the Fourier filter window is a Gaussian window, and the cut-off frequency is set to 12.5mm ^-1 . Furthermore, statistical filter (filter size: 3, filter type: median) processing is performed.

The concave portion average volume VAV is obtained by multi-region analysis. Specifically, "Region Finding Routine" is set to "By", "Threshold" is set to "0.5 μm", "Minimum Region Size" is set to "100 pixels", and "Region Level )" is set to "Valleys", "Zero Level" is set to "Automatic", "Term Removal" is set to "None", and the calculated "Volume" The value displayed in "Avg:" of "value" is adopted as the average volume VAV of the concave part. In addition, since the area level is a valley and is calculated as a negative value, the calculated average volume VAV of the concave portion is corrected to an absolute value. The root mean square height Sq is calculated using "S parpmeters-height analysis" with "Remove Tilt" set to "True". Table 2 shows the measurement results of the concave portion average volume VAV and the root mean square height Sq.

[Elongation E and Tensile Strength of Electrolytic Copper Foil] The electrolytic copper foil was cut into a rectangular shape with a width of 13.0 mm and a length of 152 mm, and this was used as a sample for measurement. Then, the tensile test of the sample for measurement was performed using a tensile tester model 1122 manufactured by Instron Corporation, and the elongation ratio and tensile strength in the normal state were measured. In this tensile test, the distance between the chucks was set to 70 mm, the tensile speed was set to 50 mm/min, and other conditions were set based on the method specified in IPC-TM-650. The results are shown in Table 2. In addition, the term "normal state" in the present invention means a state in which the electrolytic copper foil is placed in an environment of normal temperature and normal humidity (for example, a temperature of 23±2° C. and a humidity of 50±5% RH).

[Evaluation of charge-discharge cycle characteristics of lithium ion secondary batteries] For the lithium ion secondary battery, a charge-discharge cycle test was performed using a cycle of charging at a charging current of 100 mA until the voltage reached 4.2 V and discharging at a discharge current of 100 mA until the voltage reached 2.4 V 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 investigated. The results are shown in Table 2. In Table 2, the case where no breakage was observed even after 500 cycles or more was shown as "A", the case where breakage was observed after 300 cycles or more and 500 cycles or less was shown as "B", and 300 The case where breakage was observed after the second cycle was denoted as "C".

It can be said that the electrolytic copper foil, which breaks after 300 cycles, is not suitable for use as a negative electrode current collector. It can be said that the electrolytic copper foil which breaks at 300 cycles or more and 500 cycles or less is suitable for use as a negative electrode current collector. The electrolytic copper foil that does not break even after 500 cycles or more is very suitable for use as a negative electrode current collector, and can make the charge-discharge cycle characteristics of the lithium ion secondary battery good.

As can be seen from Table 2, in the lithium ion secondary batteries using the electrolytic copper foils of Examples 1 to 19 as negative electrode current collectors, since the foil thickness t of the electrolytic copper foils is 10 μm or more and 20 μm or less, VAV×t exceeds 0 μm ^. And 1000 μm ⁴ or less, E/t is 0.9%/μm or more and 1.8%/μm or less, so even if charge and discharge are repeated, the electrolytic copper foil is hardly broken, and the charge-discharge cycle characteristics of the lithium ion secondary battery are excellent.

11: Rotary electrode 12: Insoluble electrode 13: Electrolyte 14: Electrolytic copper foil

FIG. 1 is a diagram illustrating a method for producing an electrolytic copper foil using an electrolytic deposition apparatus. FIG. 2 is a diagram illustrating the electrolytic copper foil according to the present embodiment, and shows a white light interference micrograph of unevenness formed on the electrolytic desorption end surface. FIG. 3 is a diagram for explaining the electrolytic copper foil of the present embodiment, and is a diagram showing the outline of an electrolytically resolved surface on a line in the white light interference micrograph of FIG. 2 .

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Claims (10)

An electrolytic copper foil, when the foil thickness is t (μm), the average value of the volume of the concave portions formed on the electrolytic desorption end surface, that is, the average volume of the concave portions is VAV (μm ³ ), and the length along the length When the elongation ratio measured by stretching in the direction is set as E (%), and the average volume VAV of the concave portion is measured using a white light interference microscope, the foil thickness t is 10 μm or more and 20 μm or less, and the product of the average volume of the concave portion VAV and the foil thickness t That is, VAV×t is more than 0 μm ⁴ and 1000 μm ⁴ or less, and E/t obtained by dividing the elongation E by the foil thickness t is 0.9%/μm or more and 1.8%/μm or less. The electrolytic copper foil according to claim 1, wherein the product of the average volume VAV of the concave portion and the foil thickness t, that is, VAV×t is more than 0 μm ⁴ and 400 μm ⁴ or less, and is obtained by dividing the elongation E by the foil thickness t E/t is 1.2%/μm or more and 1.7%/μm or less. 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%/μm or more and 1.6%/μm or less. The electrolytic copper foil according to any one of claims 1 to 3, wherein the root-mean-square height Sq of the end surface of the electro-desorption measured using a white light interference microscope is 0.1 μm or more and 0.4 μm or less. The electrolytic copper foil according to any one of claims 1 to 3, wherein the root-mean-square height Sq of the end surface of the electro-desorption measured using a white light interference microscope is 0.1 μm or more and 0.25 μm or less. The electrolytic copper foil according to any one of claims 1 to 5, wherein the tensile strength measured by stretching in the longitudinal direction is 300 MPa or more and 380 MPa or less. 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. The electrolytic copper foil according to any one of claims 1 to 6, which is for a printed wiring board. A negative electrode for a lithium ion secondary battery comprising the electrolytic copper foil according to any one of claims 1 to 7. A lithium ion secondary battery comprising the negative electrode for a lithium ion secondary battery according to claim 9.

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