JP6067256B2 - Electrolytic copper foil, negative electrode for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

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

A lithium (Li) ion secondary battery includes, for example, a positive electrode, a negative electrode having a negative electrode active material layer formed on the surface of a negative electrode current collector, and a non-aqueous electrolyte. Used in type personal computers.
The negative electrode of the lithium ion secondary battery is formed, for example, by applying carbon particles as a negative electrode active material layer on the surface of a negative electrode current collector made of a copper foil having smooth surfaces, drying, and pressing.
As the negative electrode current collector made of the above copper foil, a so-called “untreated copper foil” produced by electrolysis is subjected to a rust prevention treatment.

As a negative electrode active material for a lithium ion secondary battery, development of a next-generation negative electrode active material having a charge / discharge capacity that greatly exceeds the theoretical capacity of a carbon material is underway.
For example, a material containing a metal that can be alloyed with lithium such as silicon (Si) or tin (Sn) is expected.

  Patent Documents 1 to 11 describe an electrolytic copper foil used for a lithium-ion secondary battery negative electrode current collector and the like.

Japanese Patent No. 3742144 Japanese Patent No. 3850155 Japanese Patent Laid-Open No. 10-255768 Japanese Patent Laid-Open No. 2002-083594 JP 2007-227328 A WO2010-110205 Japanese Patent Publication No.53-39376 Japanese Patent No. 2740768 JP-A-10-96088 JP 2009-221592 A JP 2009-299100 A

However, when it is used for active materials such as silicon, where the expansion and contraction during charging / discharging is severe, the volume change associated with insertion and extraction of lithium during charging / discharging is large. It may be difficult to maintain well. As a result, there is a problem that the current collector is destroyed and the cycle characteristics are deteriorated. As a countermeasure, it is considered that the current collector has a tensile strength or an elongation equal to or greater than a predetermined value. However, the workability (flexibility) when processing into an electronic device such as a battery, and the tensile strength, It was difficult to produce an electrolytic copper foil that balances elongation.
In order to solve the above problems, an object of the present invention is to provide an electrolytic copper foil having high strength and high flexibility.

In the transmission electron microscope (TEM) observation image, the ratio of the area occupied by the crystal particles having a particle size of 5 to 25 nm to the area occupied by the crystal particles having a particle diameter of 200 to 500 nm is 1 or more and 5 or less. A negative electrode for a lithium ion secondary battery using an electrolytic copper foil as a current collector .

Further, the present invention provides a negative electrode for a lithium ion secondary battery using an electrolytic copper foil as a current collector, and the crystal particle having a particle diameter of 5 to 25 nm and 200 to 500 nm in the transmission electron microscope (TEM) observation image. A negative electrode for a lithium ion secondary battery using an electrolytic copper foil as a current collector , wherein the proportion of the area occupied by the crystal particles excluding the crystal particles having a particle size is 10% or less of the total particles It is characterized by.

  The electrolytic copper foil preferably has a tensile strength of 500 to 900 MPa.

  The lithium ion secondary battery of the present invention is characterized by incorporating the negative electrode.

ADVANTAGE OF THE INVENTION According to this invention, the electrolytic copper foil which improved the tensile strength and the flexibility simultaneously can be provided.
In addition, by using the electrolytic copper foil of the present invention as a current collector, it is possible to provide a lithium ion secondary battery having an increased battery capacity and improved charge / discharge characteristics of the secondary battery.

FIG. 1A is a TEM image according to the embodiment, and FIG. 1B is a partially enlarged view of FIG. FIG. 2A is a TEM image according to the embodiment, and FIG. 2B is a partially enlarged view of FIG. FIG. 3A is a TEM image according to the example, and FIG. 3B is a partially enlarged view of FIG.

  The electrolytic copper foil of this embodiment is an observation image in TEM of the electrolytic copper foil, and the ratio of the area occupied by the crystal particles having a particle diameter of 5 to 25 nm to the area occupied by the crystal particles having a particle diameter of 200 to 500 nm is By setting it to 1 or more and 5 or less, tensile strength and flexibility can be improved.

Moreover, the electrolytic copper foil of the present embodiment preferably has a tensile strength of 500 to 900 MPa.
When the tensile strength is 500 to 900 MPa, sufficient durability can be ensured even when the film is thinned, and durability such as cycle characteristics is also obtained when used as a structural member for a battery using an active material such as silicon. The improvement in performance can be realized.
When the tensile strength is less than 500 MPa, the strength of the structural member is insufficient, and when it exceeds 900 MPa, defects such as cracks are likely to occur during processing.
Moreover, the electrolytic copper foil of this embodiment has a tensile strength of 600 to 800 MPa more preferably. When it is 600 to 800 MPa, durability is further enhanced, and the battery capacity can be further increased.

  Moreover, the electrolytic copper foil of this embodiment is the observation image in TEM of this electrolytic copper foil, and the area which the crystal particle except the crystal particle which is a particle size of 5-25 nm and the crystal particle which is a particle size of 200-500 nm occupies Is preferably 10% or less of the total particles, whereby the tensile strength and flexibility can be further improved, and the tensile strength and bendability suitable for high-density mounting can be improved. .

In the electrolytic copper foil of the present embodiment, the surface roughness Rz of the S surface (glossy surface) and the M surface (matte surface) of the electrolytic copper foil is 0.8 to 2.8 μm, and is 200 to 400 ° C. The 0.2% yield strength after heat treatment is preferably 250 N / mm ² or more, and the elongation is preferably 2.5% or more.
The above electrolytic copper foil has high heat resistance. Therefore, when an active material layer is applied to form a negative electrode for a lithium ion secondary battery, the adhesion between the active material and the current collector can be improved even if a polyimide binder is used, and the current collector absorbs and releases lithium. Even when the stress due to the expansion / contraction of the active material layer is received, the reduction in charge / discharge cycle efficiency of the battery is small, and the current collector can be prevented from being deformed or broken, such as wrinkles.

Moreover, when using the copper foil of this embodiment for lithium ion secondary battery negative electrode collectors, you may provide a rust prevention process layer in the surface which provides the active material layer of the said electrolytic copper foil.
The antirust treatment layer is a chromate treatment layer, or a nickel or Ni alloy plating layer, a Co or Co alloy plating layer, a Zn or Zn alloy plating layer, a Sn or Sn alloy plating layer, or a further chromate treatment layer on the above various plating layers. Or an organic rust-proofing layer such as benzotriazole.
Furthermore, a silane coupling agent treatment layer or the like may be formed.
The inorganic rust-proofing treatment, organic rust-proofing treatment, and silane coupling agent treatment increase the adhesion strength with the active material and prevent the charge / discharge cycle efficiency of the battery from decreasing.

  Further, when the copper foil of this embodiment is used for the negative electrode current collector of a lithium ion secondary battery, the surface on which the active material layer of the electrolytic copper foil is subjected to a roughening treatment, and the surface subjected to the roughening treatment May be provided with a rust-proofing layer.

[Method for producing high-strength, highly flexible electrolytic copper foil]
The electrolytic copper foil of the present embodiment includes an insoluble anode made of titanium coated with a white metal element or an oxide element thereof, and a titanium cathode drum provided to face the anode, using a sulfuric acid-copper sulfate aqueous solution as an electrolytic solution. The electrolytic solution is supplied between the electrodes, and while rotating the cathode drum at a constant speed, a direct current is passed between the two electrodes to deposit copper on the surface of the cathode drum, and the deposited copper is peeled off from the surface of the cathode drum. It is manufactured by a continuous winding method.

The electrolytic copper foil of this embodiment can be manufactured by performing electrolytic treatment in a sulfuric acid-copper sulfate electrolytic plating solution.
As a copper concentration of a sulfuric acid-copper sulfate electroplating solution, the range of 40-120 g / L is used, for example, Preferably the range of 60-100 g / L is used.
Moreover, as a sulfuric acid concentration of a sulfuric acid-copper sulfate electroplating solution, the range of 40-60 g / L is used. If the sulfuric acid concentration is less than this range, the conductivity of the plating solution is lowered, so that the throwing power of the copper foil is lowered. If it is excessive, the effect of the N (nitrogen) and S (sulfur) containing additives described below This is not preferable because the strength of the copper foil is lowered and the crystal orientation is randomized.
The chlorine concentration of the sulfuric acid-copper sulfate electroplating solution is in the range of 20-50 ppm. In addition, either or both of the following organic additives A and B are used.

The organic additive A is an organic compound containing at least one N (nitrogen) atom and S (sulfur) atom in one molecule. By adding an appropriate amount of at least one kind of the organic additive A, the amount of coarse crystal grains can be adjusted based on a metal structure having a large number of nano-sized crystal grains.
The organic additive A is desirably a thiourea compound, and more desirably a thiourea compound having 3 or more carbon atoms.
Examples of the organic additive A include thiourea (CH ₄ N ₂ S), N, N′-dimethylthiourea (C ₃ H ₈ N ₂ S), N, N′-diethylthiourea (C ₅ H ₁₂ N ₂ S). ), tetramethyl thiourea _{(C 5 H 12 N 2 S} ), thiosemicarbazide Sid _{(CH 5 N 3 S),} N- allyl thiourea _{(C 4 H 8 N 2 S} ), ethylene thiourea (C ₃ H ₆ N ₂ One or more additives selected from water-soluble thiourea such as S), thiourea such as thiourea derivatives, or thiourea derivatives can be used.

The organic additive B includes, for example, glue, gelatin, polyethylene glycol, polypropylene glycol, starch, polymer polysaccharides such as cellulose water-soluble polymer (carboxyl methyl cellulose, hydroxyethyl cellulose, etc.), polyethylene imine, polyamine polymer, etc. One or more additives selected from water-soluble polymer compounds such as polyacrylamide can be used.
By further adding the organic additive B in addition to the organic additive A, it is possible to adjust the amount of coarse crystal grains based on a metal structure having many nano-sized crystal grains.

  Furthermore, by adding a transition metal element to the sulfuric acid-copper sulfate electroplating solution, the metal element to be added, which can further improve the heat resistance, is preferably an element whose oxide is stable in a sulfuric acid aqueous solution. Desirably, it is an element capable of stably taking a trivalent or higher polyvalent oxide.

  In the present specification, the surface on the side where the electrolytic copper foil is in contact with the surface of the cathode drum at the time of manufacture is referred to as the S surface (glossy surface), and the opposite surface is referred to as the M surface (matt surface).

On the produced electrolytic copper foil (untreated copper foil), chromate treatment, Ni or Ni alloy plating, Co or Co alloy plating, Zn or Zn alloy plating, Sn or Sn alloy plating, or on the above various plating layers Further, an inorganic rust prevention treatment such as a chromate treatment or an organic rust prevention treatment such as benzotriazole.
Furthermore, the silane coupling agent process etc. are given, for example, and it uses as an electrolytic copper foil for lithium ion secondary battery negative electrode collectors.
The inorganic rust prevention treatment, organic rust prevention treatment, and silane coupling agent treatment increase the adhesion strength with the active material and prevent the charge / discharge cycle efficiency of the battery from being lowered.

Moreover, before performing said rust prevention process, a roughening process is performed to the electrolytic copper foil surface, for example. As this roughening treatment, for example, a plating method, an etching method, or the like can be suitably employed.
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. As the plating method, an electrolytic plating method and an electroless plating method can be employed.

  As the roughening by the plating method, a method of forming a plating film mainly composed of copper such as copper or copper alloy on the surface of the untreated electrolytic copper foil is preferable.

  As a roughening method by electroplating, for example, a roughening method by plating generally used for copper foils for printed circuits disclosed in Patent Document 7 is preferably used. That is, after forming a granular copper plating layer by so-called “bake plating”, “cover plating” is performed on this granular copper plating layer so as not to impair the uneven shape, thereby substantially smoothing. This is a roughening method in which a fine plating layer is deposited to turn the granular copper into a so-called bumpy copper.

As the roughening by the etching method, for example, a method by physical etching or chemical etching is suitable. For physical etching, there is a method of etching by sandblasting or the like, and for chemical etching, many liquids containing an inorganic or organic acid, an oxidizing agent, and an additive have been proposed. For example, Patent Literature 8 discloses a corrosion inhibitor such as an inorganic acid + hydrogen peroxide + triazole + a surfactant. Patent Document 9 discloses a liquid containing inorganic acid + peroxide + azole + halide.
Usually, it is a bath in which an additive such as a chelating agent is added to an acid and an oxidizing agent, and preferentially dissolves the copper grain boundaries. For example, in addition to the liquid composition disclosed in Patent Document 9, commercially available products such as CZ-8100 and 8101 of MEC Co., Ltd. and CPE-900 of Mitsubishi Gas Chemical Co., Ltd. can be adopted.

[Configuration and manufacturing method of lithium ion secondary battery negative electrode and lithium ion secondary battery using the same]
The lithium ion secondary battery negative electrode of the present embodiment uses the electrolytic copper foil for the lithium ion secondary battery negative electrode collector of the present embodiment as a current collector, and the rust-proofing layer of the current collector is formed. In this configuration, an active material layer is formed on the formed surface.

  For example, the active material layer is obtained by applying a slurry obtained by kneading an active material, a binder, and a solvent to a negative electrode current collector, drying, and pressing.

The active material layer in the present embodiment is a material that occludes / releases lithium, and is preferably an active material that occludes lithium by alloying. Examples of such an active material include carbon, silicon, germanium, tin, lead, zinc, magnesium, sodium, aluminum, potassium, and indium. Among these, carbon, silicon, germanium, and tin are preferably used because of their high theoretical capacity. Therefore, the active material layer used in the present embodiment is preferably a layer mainly composed of carbon, silicon, germanium, or tin, and in particular, a lithium ion secondary having the electrolytic copper foil of the present embodiment as a current collector. The active material that can be preferably used in the battery is silicon.
As the binder, for example, a polyimide binder can be used.

  In the present embodiment, the current collector is preferably thin, and the active material layer can be formed on one side or both sides of the current collector.

  For example, lithium may be occluded or added to the active material layer in this embodiment in advance. Lithium may be added when forming the active material layer. That is, lithium is contained in the active material layer by forming an active material layer containing lithium. Further, after forming the active material layer, lithium may be occluded or added to the active material layer. Examples of a method for inserting or adding lithium into the active material layer include a method for electrochemically inserting or adding lithium.

  Moreover, the lithium ion secondary battery of this embodiment is a lithium ion secondary battery provided with a positive electrode and a negative electrode, and the negative electrode is composed of the above-described negative electrode of the lithium ion secondary battery of this embodiment.

  The nonaqueous electrolyte used in the lithium ion secondary battery of the present embodiment is an electrolyte in which a solute is dissolved in a solvent. The solvent for the non-aqueous electrolyte is not particularly limited as long as it is a solvent used for lithium ion secondary batteries. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate And chain carbonates such as methyl ethyl carbonate. Preferably, a mixed solvent of a cyclic carbonate and a chain carbonate is used. Alternatively, a mixed solvent of the above cyclic carbonate and an ether solvent such as 1,2-dimethoxyethane or 1,2-diethoxyethane, or a chain ester such as γ-butyrolactone, sulfolane, or methyl acetate may be used. Good.

The solute of the nonaqueous electrolyte is not particularly limited as long as it is a solute used for a lithium ion secondary battery. For example, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , LiAsF ₆ , Examples thereof include LiClO ₄ , Li ₂ B ₁₀ Cl ₁₀ , and Li ₂ B ₁₂ Cl ₁₂ . In particular, LiXFy (wherein X is P, As, Sb, B, Bi, Al, Ga, or In, y is 6 when X is P, As, or Sb, and X is B, Bi, Al) , Ga, or In, y is 4.) and lithium perfluoroalkylsulfonic acid imide LiN (C _m F _{2m + 1} SO ₂ ) (C _n F _{2n + 1} SO ₂ ), where m and n Are each independently an integer of 1 to 4.) or lithium perfluoroalkylsulfonic acid methide LiC (C _p F _{2p + 1} SO ₂ ) (C _q F _{2q + 1} SO ₂ ) (C _r F _{2r + 1} SO ₂ ) (wherein p, q and r are each independently an integer of 1 to 4). Among these, a mixed solute of LiPF ₆ and LiN (C ₂ F ₅ SO ₂ ) ₂ is particularly preferably used.

As the nonaqueous electrolyte, for example, a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide, polyacrylonitrile, or polyvinylidene fluoride with an electrolytic solution, or an inorganic solid electrolyte such as LiI or Li ₃ N can be used.

  The electrolyte of the lithium ion secondary battery of the present embodiment is, for example, a lithium compound as a solute that develops ionic conductivity and a solvent that dissolves and holds the solute is not decomposed by a voltage at the time of charging, discharging or storing the battery. As long as it can be used without restriction.

Further, as the positive electrode active material used for the positive electrode, Li-containing transition metal oxides such as LiCoO ₂ , LiNiO ₂ , LiMn ₂ O ₄ , LiMnO ₂ , LiCo _0.5 Ni _0.5 O ₂ , LiNi _0.7 Co _0.2 Mn _0.1 O ₂ , Examples include metal oxides such as MnO ₂ that do not contain Li. In addition, any substance that can insert and desorb Li electrochemically can be used without limitation.

When forming a conventional carbon-based negative electrode constituent active material layer, for example, a paste made of carbon as a negative electrode active material, polyvinylidene fluoride resin as a binder, and N-methylpyrrolidone as a solvent is made on both sides of the copper foil. Apply and dry.
In this case, for example, drying is performed at a temperature of about 150 ° C. At temperatures around 150 ° C., the tensile strength, 0.2% proof stress, and elongation of the electrolytic copper foil hardly change. For example, using the electrolytic solution described in the above-mentioned Patent Document 1 to which a compound having a mercapto group, a chloride ion, and a low molecular weight glue having a molecular weight of 10,000 or less and a high molecular weight polysaccharide are added to a copper sulfate-sulfuric acid electrolyte. The produced electrolytic copper foil has a 10 μm foil having a tensile strength at room temperature of 300 to 350 N / mm ² , but its performance hardly changes even when it is dried at a temperature of around 150 ° C.
Furthermore, as described above, in the case of a carbon active material, the volume expansion at the time of charging / discharging is at most about 10%, so that the charging / discharging cycle efficiency is remarkably reduced, or the current collector is deformed or broken by charging / discharging. There is no such thing as to do.

Moreover, the 10-micrometer-thick electrolytic copper foil manufactured from the copper sulfate-sulfuric acid electrolyte solution described in Patent Document 2 has a tensile strength at room temperature of about 570 N / mm ² and an elongation of about 7%. However, when drying is performed at a temperature of about 150 ° C., the performance changes, the tensile strength is about 230 N / mm ² , and the elongation is about 25%. However, in the case of a carbon active material, the volume expansion at the time of charging / discharging is at most about 10%. Therefore, even when the foil has a low tensile strength and a large elongation, the charging / discharging cycle efficiency is remarkably reduced, or charging / discharging The current collector does not deform or break.

On the other hand, for example, when a silicon-based material containing silicon is used as an active material, a polyimide-based resin may be used as a binder in order to prevent expansion and contraction of the active material during charge / discharge. In this case, the drying and curing temperature is higher than that when a carbon-based active material is used. For example, the drying and curing are performed at a temperature of about 200 ° C. to 400 ° C. for about 0.5 to 1.5 hours.
When heat treatment is performed at a high temperature as described above, in the electrolytic copper foils of Patent Document 1 and Patent Document 2 described above, the foil is annealed and softened, and the charge / discharge cycle efficiency is remarkably reduced. Due to the expansion and contraction, the foil is likely to be deformed and broken.

  When the foil is deformed, it can be considered that the foil is subjected to stress above the yield point. The yield point is the stress at which the elasticity changes to plasticity. Even if the foil is subjected to stress in the elastic region, no deformation occurs. However, it deforms when stress in the plastic region is applied.

  Therefore, even after the foil is heated by drying and curing, in the case of a foil having a large yield point, the active material expands and contracts due to charge and discharge, and deformation occurs even when stress is applied to the foil as a current collector. Is unlikely to occur.

Therefore, as described in Patent Document 6 above, even when an electrolytic copper foil having a tensile strength of 400 N / mm ² or more and an elongation of 4.5% to 13% at room temperature is used, it is not always due to charge / discharge. It cannot be said that deformation does not occur in the foil due to expansion and contraction. It can be said that a foil having a large yield point even after drying and curing is a foil that does not cause foil deformation.

  Here, the yield point is measured by a tensile test, but this point is not clear in the case of an electrolytic copper foil. In such a case, usually the value when 0.2% strain is generated is taken and substituted for the yield point. This is called 0.2% proof stress.

In the case of an electrolytic copper foil, having a large 0.2% yield strength at room temperature does not necessarily coincide with having a large yield point even after heating. For example, the foil shown in Comparative Example 2 of Table 2 is a foil was prepared based on Patent Document 2, high tensile strength at room temperature (510N / mm ²⁾ 0.2% yield strength of (345N / mm ²⁾ with, but after heating annealed soften tensile strength (204N ^/ mm 2), it becomes small foil 0.2% yield strength (102N / mm ^2).

As described in Patent Document 6, even a material having a tensile strength at room temperature of 400 N / mm ² or more is not preferable for a material that is annealed by heating and has a 0.2% yield strength. It is important that the 0.2% yield strength after heating has a certain value or more.
Moreover, when elongation is small, there exists a tendency for the fall of charging / discharging cycle efficiency to be large while repeating charging / discharging cycle many times.
In order to reduce the decrease in charge / discharge cycle efficiency, it is preferable that the 0.2% yield strength is 250 N / mm ² or more and the elongation is 2.5% or more.

  In this embodiment, the tensile strength is a value measured by a method defined in the IPC standard (IPC-TM-650).

[Example]
[Manufacture of untreated copper foil]
An additive solution having the composition shown in Table 1 was added to an acidic copper electrolytic bath of copper 80 g / L-sulfuric acid 40-60 g / L to prepare an electrolytic solution for foil production. In the examples, the chloride ion concentration was all adjusted to 30 ppm, but the chloride ion concentration is appropriately changed depending on the electrolysis conditions, and is not limited to this concentration.
Using the prepared electrolytic solution, a noble metal oxide-coated titanium electrode for the anode, and a titanium rotating drum for the cathode, under the electrolysis conditions (current density, liquid temperature) shown in Table 1, 20 μm-thick untreated copper The untreated copper foil of Examples 1-9 was manufactured by the foil-making method.
Moreover, unprocessed copper foil was manufactured so that it might become 20 micrometers with the electrolyte solution of the composition shown in Table 1 also in Comparative Examples 1-4, and unprocessed copper foil was manufactured.
Here, 2M-5S is 2-mercapto-5-benzimidazolesulfonic acid, SPS is bis (3-sulfopropyl) disulfide, and DDAC is diallyldimethylammonium chloride.

[Measurement of characteristics of electrolytic copper foil]
Tensile strength (MPa) of each electrolytic copper foil (Examples 1 to 9, Comparative Examples 1 to 4), measurement of the area ratio occupied by particles belonging to a specific particle size range calculated from the TEM image, and IPC test, A comprehensive evaluation was conducted. The results are shown in Table 2.
The tensile strength was measured using a tensile testing machine (Instron type 1122).

In addition, the crystal grain existing area ratio was measured and observed with a transmission electron microscope (JEM-3010 manufactured by JEOL Ltd.) with an acceleration voltage of 300 kV and an observation field of view of 200 to 400,000 times. The crystal grain size was determined.
An observation sample was prepared using TenuPol-5 (Struers).
Temperature: −26 to −25 ° C., voltage: 8 V, electrolyte; nitric acid: methanol = 1: 2.
The measurement of the area ratio of crystal grains belonging to a specific particle size range by TEM is performed by measuring the area ratio (%) of crystal grains having a particle diameter of 5 to 25 nm and the area ratio of crystals having a particle diameter of 200 to 500 nm. (%), The area ratio (%) which is the other particle size was calculated. From this value, the ratio of the area occupied by crystal grains having a particle diameter of 5 to 25 nm to the area occupied by crystal grains having a particle diameter of 200 to 500 nm was determined.
In addition, the evaluation of flexibility is based on IPC-TM-650, bending speed: 1500 times / minute, bending stroke: 20 mm, test direction: MD, sample width: 15 mm, bending radius: 1.0 mm, until breakage Was measured and indicated as the number of times (× 10 ⁶ times).

FIG. 1A is a TEM image according to the embodiment, and FIG. 1B is a partially enlarged view of FIG.
2A is a TEM image according to the embodiment, and FIG. 2B is a partially enlarged view of FIG.
Moreover, Fig.3 (a) is a TEM image which concerns on an Example, FIG.3 (b) is a partially expanded view of Fig.3 (a).
As shown in FIG. 1 to FIG. 3, crystal particles having different particle diameters exist on the structure to be observed, and the ratio of the crystal particle existing area was measured based on the TEM image by the line intercept method.
In the comprehensive evaluation, a case where the tensile strength and the IPC test result are both good is Δ, a case where the tensile strength is good is ○, and a case where any one is poor is ×.

As shown in Table 2, in the TEM image, the ratio of the area occupied by the crystal particles having a particle diameter of 5 to 25 nm to the area occupied by the crystal particles having a particle diameter of 200 to 500 nm is 1 or more and 5 or less. 1 to 9 had good tensile strength and IPC test results.
On the other hand, in Comparative Examples 1 to 4, either the tensile strength or the IPC test result was defective.

  Since the electrolytic copper foil of the present invention has tensile strength and bendability suitable for high-density mounting, it can be suitably used for electronic devices.

Claims (4)

In the transmission electron microscope (TEM) observation image, the ratio of the area occupied by the crystal particles having a particle diameter of 5 to 25 nm to the area occupied by the crystal particles having a particle diameter of 200 to 500 nm is 1 or more and 5 or less. A negative electrode for a lithium ion secondary battery using the electrolytic copper foil as a current collector . The negative electrode for a lithium ion secondary battery using the electrolytic copper foil according to claim 1 as a current collector , the crystal particle having a particle diameter of 5 to 25 nm and 200 to 500 nm in the transmission electron microscope (TEM) observation image A negative electrode for a lithium ion secondary battery using an electrolytic copper foil as a current collector , wherein the proportion of the area occupied by crystal particles excluding crystal particles having a particle size of 10% or less is 10% or less of all particles. The negative electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the electrolytic copper foil has a tensile strength of 500 to 900 MPa. The lithium ion secondary battery incorporating the negative electrode which made the collector the electrolytic copper foil in any one of Claims 1-3.