JP2013133514A - Copper foil, electrode for secondary battery, secondary battery, and printed circuit board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil for an negative electrode of a lithium ion secondary battery, which allows the production of a lithium ion secondary battery causing no decrease in capacity even if charge and discharge cycles are repeated, having a long life and prevented from being deformed in a negative electrode collector.SOLUTION: The analysis of the copper foil in the depth direction by SIMS (Secondary Ion Mass Spectroscopy) in the foil thickness direction shows that the copper foil includes each of chlorine and carbon in a concentration of 10to 5×10atoms/cmand sulfur or/and nitrogen in a concentration of 10to 5×10atoms/cm. By using the copper foil in a negative electrode collector of a Li ion battery, a lithium ion secondary battery can be provided in which the generation of deformation such as wrinkle in the collector caused by charge and discharge is suppressed, which causes no decrease in capacity even if charge and discharge cycles are repeated and which has long life and can be made compact.

Description

  The present invention relates to a copper foil preferably used for non-aqueous electrolyte secondary batteries such as printed circuit boards and lithium ion secondary batteries.

  A non-aqueous electrolyte secondary battery comprising a positive electrode and a negative electrode current collector made of copper foil having a smooth both surfaces, coated with carbon particles as a negative electrode active material layer, dried and further pressed, and a non-aqueous electrolyte; In particular, lithium ion secondary batteries are currently used in mobile phones, notebook computers and the like. As the negative electrode current collector of this non-aqueous electrolyte secondary battery (lithium ion secondary battery), a so-called “untreated electrolytic copper foil” produced by electrolytic deposition is used for rust prevention treatment. Has been.

  As shown in Patent Document 1, the copper foil as the negative electrode current collector for a lithium ion secondary battery has a reduced surface roughness difference between a glossy surface and a rough surface (both surfaces of the copper foil). By using the foil, a decrease in charge / discharge efficiency of the battery is suppressed.

The electrolytic copper foil with a small difference in surface roughness between the glossy surface and the rough surface as described above is composed of various water-soluble polymer substances, various surfactants, various organic sulfur compounds, chlorides, and copper sulfate-sulfuric acid electrolytes. It is manufactured by appropriately selecting and adding physical ions.
For example, Patent Document 1 uses an electrolytic copper foil produced by adding 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 to a copper sulfate-sulfuric acid electrolyte. A negative electrode current collector was disclosed.
The electrolytic copper foil produced by the above production method is coated with carbon particles on the surface of the copper foil, dried, and then pressed to form a negative electrode.
This electrolytic copper foil has a tensile strength of 300 to 350 N / mm ² , and is a suitable material in combination with appropriate elongation when used as a negative electrode copper foil using the carbon particles as an active material.

  By the way, in recent years, for the purpose of increasing the capacity of lithium ion secondary batteries, which are representative of nonaqueous electrolyte secondary batteries, metal negative electrodes such as tin and silicon that are electrochemically alloyed with lithium during charging are used as negative electrodes. Patent Document 2 discloses a lithium ion secondary battery used as an active material.

A negative electrode for a lithium ion secondary battery for the purpose of increasing the capacity is obtained by depositing, for example, silicon on an amorphous silicon thin film or microcrystal on a current collector such as a copper foil by vapor deposition, sputtering, CVD, or the like. It is deposited and formed as a silicon thin film. It has been found that the thin film layer of the active material produced by such a method is in close contact with the current collector, and thus exhibits good charge / discharge cycle characteristics (see Patent Document 3).
In recent years, Patent Document 4 has also developed a method in which powdered silicon or a silicon compound is formed into a slurry using an imide-based binder and an organic solvent, applied onto a copper foil, dried, and pressed.

However, in such an electrode for a lithium ion secondary battery, for example, the silicon active material expands to a volume of about 2 to 4 times by electrochemically alloying lithium ions during charging, and further the lithium ions are Shrinks during discharge.
Due to the expansion and contraction of the volume of the active material layer accompanying such charge and discharge, there is a phenomenon that the active material is pulverized and peeled off from the current collector.
In addition, since the active material layer is in close contact with the current collector, when the volume of the active material layer expands and contracts due to repeated charging and discharging, a large stress acts between the electrode coating film and the current collector, and the coating film And peeling occurs at the current collector interface, or a part of the coating film is detached. In addition, wrinkles may occur in the current collector, and when charging and discharging are repeated many times, there is a problem that the foil as the current collector is broken in the worst case.

  When deformation such as wrinkles occurs in the current collector, the positive electrode and the negative electrode are easily short-circuited. Further, when the current collector breaks, it becomes impossible to maintain stable battery performance for a long time.

Conventionally, it has been proposed to use a copper foil having a high tensile strength and a large elongation at break in response to such problems. That is, Patent Document 5 discloses a lithium ion secondary battery using an electrolytic metal foil having a tensile strength of 400 N / mm ² or more or a breaking elongation of 7% or more as a current collector.

  Patent Document 5 describes an example in which carbon is used as an active material. In the case of a carbon active material, volume expansion of about 10% occurs during charging, but is smaller than that of a silicon active material or the like. Therefore, it cannot be said that the copper foil having the performance described in Patent Document 5 is sufficient when used as a silicon active material.

Japanese Patent No. 3742144 Japanese Patent Laid-Open No. 10-255768 Japanese Patent Laid-Open No. 2002-083594 JP 2007-227328 A JP 2001-189154 A

As described above, when the negative electrode having an active material layer mainly composed of carbon such as graphite, tin, or silicon formed on a current collector as an electrode for a lithium ion secondary battery, the active material accompanies the charge / discharge reaction. In some cases, the volume of the layer expands and contracts, and a large stress acts on the current collector to cause deformation such as wrinkles in the current collector. Furthermore, when charging and discharging was repeated many times, there was a problem that the foil as a current collector was broken.
When the current collector is deformed, such as wrinkles, the active material is detached, the chargeable / dischargeable capacity is reduced, and the battery life is reduced. Further, when the current collector is broken, the conductive path is cut, and the basic battery performance and electrode characteristics for charging and discharging are drastically deteriorated.

  The present invention provides a lithium ion secondary battery (non-aqueous electrolyte secondary battery) using a negative electrode in which an active material layer mainly composed of tin or silicon is formed on a copper foil as a current collector. An object of the present invention is to provide a lithium ion secondary battery that is excellent in discharge cycle efficiency, does not cause wrinkles in the current collector, and maintains stable performance for a long time without causing breakage of the current collector. It is an object of the present invention to provide an electrode for use as well as an electrolytic copper foil constituting a current collector of the electrode. Another object of the present invention is to provide an electrolytic copper foil that is excellent for printed circuits, particularly for flexible printed circuits and fine pattern circuits.

  In the present invention, depending on the amount of chlorine, carbon, oxygen, sulfur, and nitrogen contained in the copper foil, the tensile strength of the copper foil, 0.2% yield strength, tensile strength after heating at 200 to 400 ° C., and 0.2% yield strength As a result, the present invention has been found.

The copper foil of the present invention contains chlorine (Cl) and carbon (C) in a concentration of 10 ^{17 to} 5 × 10 ²⁰ atoms / cm ³ , and sulfur (S) and / or nitrogen (N) in a range of 10 ^{15 to} 5 × 10. A copper foil containing ¹⁹ atoms / cm ^{3 and} containing oxygen O at a concentration of 5 × 10 ²⁰ atoms / cm ³ or less.
In addition, these elements contained in the copper foil can be measured by a depth profile (depth direction) analysis by a secondary ion mass spectrometer (SIMS) in the thickness direction of the copper foil.

The minimum crystal grain size of the copper foil in the thickness direction cross section is preferably 500 nm or less, and the maximum is 2500 or less.
In addition, the crystal grain diameter of copper foil can be measured from a scanning ion microscope (Scanning ion microscope: SIM) image.

The copper foil preferably has a 0.2% proof stress of 250 N / mm ² or more after heating at 200 to 400 ° C. for 30 minutes to 1.5 hours.

  The copper foil is an electrolytic copper foil or a rolled electrolytic copper foil obtained by further rolling the electrolytic copper foil.

  The negative electrode of the non-aqueous electrolyte secondary battery of the present invention has a rust preventive treatment on at least one surface of the copper foil of the present invention, or a rough treatment on at least one surface to prevent the roughened surface. It is an electrode in which an active material layer is deposited on a surface that has been rust-treated and subjected to the rust-proofing treatment.

  The active material layer constituting the negative electrode is formed of an active material containing carbon, silicon, tin, aluminum, magnesium, or calcium as a main component.

  The nonaqueous electrolyte secondary battery of the present invention is a battery incorporating the negative electrode of the present invention.

  The printed or flexible printed circuit board of the present invention is a circuit board formed by laminating the copper foil of the present invention with an insulating substrate.

  The lithium ion secondary battery of the present invention can withstand the large stress on the current collector and the expansion and contraction of the active material layer accompanying the charge / discharge reaction by using the copper foil for the negative electrode current collector of the battery. Thus, it is possible to provide a long-life nonaqueous electrolyte secondary battery (lithium ion secondary battery) that does not cause deformation such as wrinkles in the current collector and has little battery performance deterioration.

  The present invention relates to a nonaqueous electrolyte secondary battery (lithium ion secondary battery) using a negative electrode in which an active material layer mainly composed of tin or silicon is formed on a copper foil as a current collector. An object of the present invention is to provide a lithium ion secondary battery that is excellent in discharge cycle efficiency, does not cause wrinkles in the current collector, and maintains stable performance for a long time without causing breakage of the current collector. It is possible to provide an electrode for use as well as a copper foil constituting a current collector of the electrode.

  The present invention can also provide a copper foil that is excellent for printed circuits, particularly for flexible printed circuits and fine pattern circuits.

It is the image which image | photographed the thickness direction cross section of copper foil with the scanning ion microscope (SIM). It is the schematic diagram explaining the distance d from the boundary to the magnitude | size of the crystal grain comprised by the crystal | crystallization boundary of a copper foil.

The copper foil of the present invention has been intensively studied on the relationship between the contents of chlorine, carbon, oxygen, sulfur, and nitrogen contained in the copper foil and the mechanical strength, and as a result, chlorine and carbon were each 10 ^{17 to} 5 × 10 ^20. A copper foil containing an atom / cm ³ concentration, containing sulfur or / and nitrogen at a concentration of 10 ^{15 to} 5 × 10 ¹⁹ atoms / cm ^{3 and} containing oxygen at a concentration of 5 × 10 ²⁰ atoms / cm ³ or less has excellent mechanical strength. In particular, the copper foil is a copper foil having an excellent 0.2% proof stress of 250 N / mm ² or more when heated at 200 ° C. to 400 ° C. for 0.5 to 1.5 hours.

  In addition, the electrolytic copper foil from which the content of the atoms deviated could not satisfy the mechanical strength. The superiority or inferiority of the mechanical strength will be described in Examples and Comparative Examples described later, but the theory and cause have not been pursued.

The atomic content measurement is a result of analysis in a depth profile (depth direction) with a secondary ion mass spectrometer (SIMS) in the copper foil thickness direction.
The copper foil of the present invention is preferably a copper foil having a cross-sectional observation crystal grain size of 500 nm or less and a maximum of 2500 or less in the thickness direction of the copper foil. Cross-sectional observation in the thickness direction of the copper foil The crystal grain size was measured with a scanning ion microscope (SIM) image.

  The copper foil of the present invention exhibits an excellent effect as a current collector for depositing an active material having a large expansion / contraction, which is particularly employed for an electrode of a non-aqueous secondary battery.

When forming a conventional carbon-based negative electrode constituent active material layer, a paste made of carbon as a negative electrode active material, polyvinylidene fluoride resin as a binder, N-methylpyrrolidone as a solvent is applied to both sides of the copper foil, Dry.
In this case, the active material deposited on the current collector is dried at a temperature of about 150 ° C. At a temperature 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 Patent Document 1 described above, in 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 electrolytic solution. The manufactured 10 μm thick electrolytic copper foil has a tensile strength at room temperature of 300 to 350 N / mm ² , and its performance hardly changes even when dried at a temperature of around 150 ° C.
Further, as described above, in the case of the carbon active material, the volume expansion at the time of charging / discharging is at most about 10%. There is no such thing as to do.

On the other hand, when silicon (silicon-based) is used as the active material, a polyimide-based resin may be used for the 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, and drying and curing are performed at a temperature of about 200 ° C. to 400 ° C.
When heating is performed at such a high temperature, the electrolytic copper foil disclosed in Patent Document 1 and Patent Document 2 is annealed and softened, the charge / discharge cycle efficiency is significantly reduced, and the active material expands during charge / discharge. Shrinkage tends to cause deformation and breakage of the foil.

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 has been heated by drying and curing, if the foil has a large yield point, the silicon active material expands and contracts due to charge and discharge, and stress is applied to the foil that is the current collector. , Deformation is unlikely to occur.

Therefore, as described in Patent Document 5, the tensile strength is 400 N / mm ² or more at room temperature or the elongation at break is 7% or more at room temperature, and the product of the tensile strength and the elongation at break is 2800 N / mm ² ·%. Constructing a lithium-ion secondary battery using the above electrolytic metal foil is not effective in preventing foil deformation due to charge / discharge, but it is a foil with a large yield point even after drying and curing. It can be said that the foil does not cause 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 defined as 0.2% yield strength.

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 foil shown in Comparative Example 4 in Table 2 below, which have high tensile strength at room temperature (510N / mm ²⁾ 0.2% yield strength (345N / mm ^2), it is annealed to soften after heating Te tensile strength (204N ^/ mm 2), becomes small foil 0.2% yield strength (102N / mm ^2).

As described in Patent Document 5, even a material having a tensile strength at room temperature of 400 N / mm ² or more is meaningless in 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 is above a certain value. When the elongation is small, the current collector (foil) breaks while the charge / discharge cycle is repeated many times. In order not to cause the breakage of the foil, 250 N / mm ² or more is required at 0.2% proof stress, and the elongation is required to be 2.5% or more.

The copper foil of the present invention is a copper foil having a 0.2% proof stress of 250 N / mm ² or more. Therefore, when such a copper foil is used as a current collector, even if it receives stress due to expansion / contraction of the active material layer due to insertion / extraction of lithium, the current collector will not be deformed or broken such as wrinkles. .
The mechanical properties of the copper foil of the present invention include chlorine and carbon in concentrations of 10 ^{17 to} 5 × 10 ²⁰ atoms / cm ³ , oxygen O in concentrations of 5 × 10 ²⁰ atoms / cm ³ or less, sulfur or And nitrogen is contained at a concentration of 10 ^{15 to} 5 × 10 ¹⁹ atoms / cm ³ .
Quantification of these elements can be determined by analyzing the depth profile (depth direction) with a secondary ion mass spectrometer (SIMS) in the foil thickness direction.

  The analysis by SIMS can analyze elements by irradiating and sputtering primary ions on the sample surface and mass-analyzing secondary ions emitted from the surface. It is also possible to analyze the concentration of the profile in the depth direction with high sensitivity. Cesium ions, oxygen ions, and argon ions are used for the primary ion beam. The quantification of the component concentration is grasped by comparing these analysis results with a standard sample.

Furthermore, as for the copper foil of this invention, as a result of taking out a cross section by FIB (focused ion beam) and observing and confirming the particle size from a clear image by a scanning ion microscope (SIM) image, the cross-sectional observation crystal particle size is 4000 nm or less, A copper foil in the range of 20 to 3500 nm is desirable.
The crystal grain size in the present invention is defined as the distance d shown in FIG. 2 in the crystal grain composed of the crystal-crystal boundary shown in FIG.

Moreover, it is desirable that the copper foil of the present invention is an electrolytic copper foil produced by an electrolytic deposition method. This is because each element described above can be effectively incorporated into the copper foil by electrodeposition by manufacturing by electrolytic deposition. Moreover, it is also desirable that it is the copper foil which rolled the electrolytic copper foil.
In addition, although it can manufacture also with rolled copper foil, it is a little difficult to take in each element effectively as prescribed | regulated.

In the present invention, the tensile strength, 0.2% proof stress, and elongation are values measured by a method defined in Japanese Industrial Standard (JIS K 6251).
The surface roughness Rz is a ten-point average roughness defined in Japanese Industrial Standards (JIS B 0601-1994), and is a value measured by, for example, a stylus type surface roughness meter.

  The electrolytic copper foil of the present invention comprises, for example, a sulfuric acid-copper sulfate aqueous solution as an electrolytic solution, 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. 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 the present invention can be produced by adding thioureas, polymer polysaccharides, and chloride ions to a sulfuric acid-copper sulfate electrolytic solution.

The manufactured electrolytic copper foil is subjected to inorganic rust prevention treatment such as chromate treatment, organic rust prevention treatment such as benzotriazole, silane coupling agent treatment, and the like to obtain a product.
The above inorganic rust prevention treatment, organic rust prevention treatment, and silane coupling agent treatment are rust prevention on the surface of copper foil, improvement of adhesion to insulating resin substrate, improvement of adhesion strength with active material, capacity maintenance rate during charge / discharge of battery It plays the role of preventing the decrease of

Moreover, the surface roughness of the electrolytic copper foil surface is set to Rz = 0.8 to 2.8 μm, which is suitable when, for example, a silicon-based active material is laminated. The surface roughness is adjusted by roughening the surface. As this roughening treatment, 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 electrolytic copper foil. As the plating method, an electrolytic plating method or an electroless plating method can be employed.

  As the surface 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 electrolytic copper foil is preferable.

  As a roughening method by electroplating, for example, a roughening method by plating generally used for copper foil for printed circuits disclosed in Japanese Patent Publication No. 53-39376 is preferably used. That is, after a granular copper plating layer is formed by so-called “bake plating”, “capsule plating” is performed on the granular copper plating layer so as not to impair the uneven shape, thereby substantially smoothing. This is a roughening method in which a fine plated layer is deposited to make the granular copper into so-called bumpy copper.

As the roughening by the etching method, 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, a liquid containing an inorganic or organic acid, an oxidizing agent and an additive is used as a processing liquid. For example, Japanese Patent No. 2740768 describes a corrosion inhibitor such as an inorganic acid + hydrogen peroxide + triazole + a surfactant. Japanese Patent Application Laid-Open No. 10-96088 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 the above-mentioned patent document, 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.

The case where the copper foil of the present invention is used as a current collector of a lithium ion secondary battery will be described.
The active material layer deposited on the current collector surface is a material that occludes and releases lithium, and is preferably an active material that occludes lithium by alloying. Examples of such an active material include silicon, germanium, tin, zinc, magnesium, sodium, and aluminum. Among these, carbon, silicon, and tin are preferably used because of their high theoretical capacity. Accordingly, the active material layer used in the present invention is preferably a layer mainly composed of silicon, carbon, or tin, and particularly preferably a silicon layer.

  The active material layer is preferably formed by slurrying the active material together with a binder and a solvent, coating, drying, and pressing.

  The current collector is preferably thin, and the active material layer can be deposited on one or both sides of the current collector.

  Lithium may be occluded or added in advance to the active material layer. 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.

  The nonaqueous electrolyte used in the lithium ion secondary battery is an electrolyte in which a solute is dissolved in a solvent. The solvent for the nonaqueous electrolyte is not particularly limited as long as it is a solvent used in a lithium ion secondary battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate, dimethyl carbonate, and 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 non-aqueous electrolyte, 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 a lithium ion secondary battery should be used without restriction unless the Li compound as a solute that develops ionic conductivity and the solvent that dissolves and retains it are decomposed by the voltage at the time of battery charging, discharging or storage. Can do.

Further, as the positive electrode active material used for the positive electrode, lithium-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 lithium. In addition, any substance that electrochemically inserts and desorbs lithium can be used without limitation.

  By using the copper foil of the present invention as a current collector, the current collector can be prevented from being deformed or broken due to charging / discharging, and stable battery performance and electrode characteristics can be maintained for a long period of time. A non-aqueous electrolyte secondary battery (lithium ion secondary battery) can be provided.

Hereinafter, specific examples of the present invention will be described based on examples. However, the present invention is not limited to the following examples, and can be appropriately modified and implemented without departing from the scope of the invention.
[Examples 1 to 10, Comparative Examples 1 to 4]

[Manufacture of copper foil]
Additives having the composition shown in Table 1 were added to an acidic copper electrolytic bath of copper 70 to 130 g / l-sulfuric acid 80 to 140 g / l. In the table, the kind of additive A is thiourea, NN′-dimethylthiourea, tetramethylthiourea, ethylenethiourea, and the kind of additive B is polyacrylamide, polyethyleneimine, gelatin, polyethylene glycol, hydroxyethylcellulose. In the additive of the comparative example, only MPS (sodium 1-mercapto-3-propanesulfonate), gelatin, HEC (hydroxyethylcellulose) is used, and the chloride ion has a concentration shown in Table 1, Each was added to prepare an electrolytic solution for foil production. Although the chloride ion concentration was adjusted to 30 ppm, the chloride ion concentration is appropriately changed depending on the electrolysis conditions, and is not limited to this concentration.

Using the prepared electrolyte, a noble metal oxide-coated titanium electrode for the anode, and a titanium rotating drum for the cathode, and 18 μm-thick untreated copper under the electrolysis conditions (current density, liquid temperature) shown in Table 1 Copper foils of Examples 1 to 4 and Comparative Example 1 were produced by electrolytic foil production. Similarly, about Examples 5-10, 20 micrometer untreated copper foil was manufactured as weight thickness.
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 for Comparative Examples 2-3.

[Creation of negative electrode current collector]
The surface of the electrolytic copper foil shown in Table 1 was subjected to copper burnt plating by electroplating to form a granular copper plating layer. Furthermore, smooth copper plating (capsule plating) is performed on the granular powder copper plating layer so as not to impair the irregular shape, and the roughened surface improves the adhesion between the granular copper and the copper foil. Copper foil was created.
As described above for Examples 1 to 4 and Comparative Example 1, an untreated copper foil having an initial thickness of 18 μm was prepared, and then copper burnt plating and capsule plating by electroplating were performed so that the thickness became 20 μm. A surfaced electrolytic copper foil was prepared, subjected to chromate treatment, and then used as a current collector.

On the other hand, for Examples 5 to 10 and Comparative Examples 2 to 4, a 20 μm untreated copper foil was prepared, and then the copper burnt plating and the capsule plating were not performed, and only the chromate treatment was performed, did.
In other words, the thicknesses of Examples 1 to 10 and Comparative Examples 1 to 4 were adjusted to 20 μm when they were current collectors.
The conditions for burnt plating (granular powder plating), capsule plating (smooth copper plating), and chromate treatment for roughening the copper foil surface are as follows.

[Burn plating (granular powder plating) conditions]
Copper sulfate 80-140g / L
Sulfuric acid 110-160g / L
Additive Appropriate amount Liquid temperature 30-60 ° C
Current density 10-50A / dm ²
Processing time 2 to 20 seconds

[Capsule (smooth copper plating) conditions]
Copper sulfate 200-300g / L
Sulfuric acid 90 ~ 130g / L
Liquid temperature 30-60 ° C
Current density 10-30A / dm ²
Processing time 2 to 20 seconds

[Chromate treatment conditions]
Potassium dichromate 1-10g / L
Immersion treatment time 2 to 20 seconds

  Table 2 shows the tensile strength, 0.2% proof stress, elongation, and surface roughness Ra and Rz of each of the examples and comparative examples.

The tensile strength, 0.2% proof stress, and elongation are values measured using a tensile tester (Model 1122 manufactured by Instron). The surface roughness Ra and Rz are values measured by a stylus type surface roughness meter (SE-3C type manufactured by Kosaka Laboratory).

  Table 3 shows the results of depth direction analysis by SIMS for the copper foils of each of the examples and comparative examples. In addition, the value of the crystal grain size by observation of a FIB (focused ion beam) cross-section SIM image is also shown. I wrote.

[Create negative electrode]
Using silicon powder (purity 99.9%) having an average particle diameter of 15 μm as the negative electrode active material particles, using polyimide as the binder, the negative electrode active material particles and the binder have a weight ratio of 9: 1. In addition to N-methyl-2-pyrrolidone, these were mixed to prepare a negative electrode mixture slurry.

  Next, the negative electrode mixture slurry was applied onto a copper foil serving as a current collector and dried to form negative electrode mixture layers on both sides of the negative electrode current collector. The electrode thickness at this time was 85 μm.

  Then, after rolling to an electrode thickness of 60 μm using a rolling roller, this was sintered at each temperature shown in Table 1 for 1 hour in an argon atmosphere to prepare a negative electrode.

[Preparation of positive electrode]
In producing the positive electrode active material, Li ₂ Co ₃ and CoCo ₃ were used and weighed so that the atomic ratio of Li: Co was 1: 1, and these were mixed in a mortar. After pressing with a mold and pressure forming, this is fired in air at a temperature of 800 ° C. for 24 hours to produce a LiCoO ₂ fired body, and this LiCoO ₂ fired body is pulverized in a mortar, LiCoO ₂ powder having an average particle size of 20 μm was obtained.

Then, 5 parts by weight of N-methyl-containing 5 parts by weight of an artificial graphite powder as a conductive agent and 3 parts by weight of polyvinylidene fluoride as a binder with respect to 90 parts by weight of the positive electrode active material particles made of this LiCoO ₂ powder. A 2-pyrrolidone solution was mixed to prepare a positive electrode mixture slurry.

  Next, this positive electrode mixture slurry was applied to a positive electrode current collector made of 15 μm aluminum foil, dried and rolled to produce a positive electrode in which a positive electrode mixture layer was formed on both surfaces of the positive electrode current collector.

[Preparation of non-aqueous electrolyte]
In preparing the non-aqueous electrolyte, LiPF ₆ was dissolved to a concentration of 1 mol / liter in a mixed solvent in which ethylene carbonate and diethylene carbonate were mixed at a volume ratio of 3: 7, and further 25 ° C. In this case, carbon dioxide was blown for 10 minutes to dissolve the carbon dioxide until the saturation amount was reached.

[Evaluation of battery charge / discharge characteristics]
A lithium ion secondary battery was prepared using the negative electrode, the positive electrode, and the non-aqueous electrolyte, and the charge / discharge characteristics were evaluated.
In producing a lithium ion secondary battery, a positive electrode current collector tab made of aluminum is attached to the positive electrode, and a negative electrode current collector tab made of nickel is attached to the negative electrode. The positive electrode and the negative electrode are made of polyethylene porous material. The electrode body was produced by winding so as to face each other through a separator made of a body.

  Next, the electrode body is inserted into an exterior body made of an aluminum laminate film, and the nonaqueous electrolyte is added to the exterior body. Thereafter, the positive electrode current collection tab and the negative electrode current collection tab are externally attached. As described above, the opening of the outer package was sealed.

  Next, each of the lithium ion secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 4 manufactured as described above was subjected to a current value of 1000 mA in a 25 ° C. atmosphere at 4 mA. After charging to 2V, at a current value of 1000 mA, 2. The battery was discharged to 75 V, and charging and discharging were repeated as one cycle. The number of cycles until the discharge capacity reached 70% of the discharge capacity at the first cycle was measured, and this was defined as the cycle life. The results are shown in Table 4 using an index with the cycle life of the lithium ion secondary battery of Example 1 as 100.

  In addition, each of the lithium secondary batteries of Examples 1 to 10 and Comparative Examples 1 to 4 after the cycle was disassembled, and the presence or absence of wrinkles in the negative electrode current collector of each negative electrode was examined. Showed.

As shown in Table 4, in Examples 1 to 10 of the present invention, the result of SIMS depth direction analysis of the copper foil in the thickness direction was 10 ^{17 to} 5 × 10 ²⁰ atoms / cm ³ concentration of chlorine Cl, carbon C: 10 ^{17 to} 5 × 10 ²⁰ atoms / cm ³ concentration, oxygen O: 10 ^{17 to} 5 × 10 ²⁰ atoms / cm ³ concentration, sulfur S: 10 ^{15 to} 5 × 10 ¹⁹ atoms / cm ³ concentration, nitrogen N By using the copper foil containing 10 ^{15 to} 5 × 10 ¹⁹ atoms / cm ³ concentration, it is confirmed that the capacity does not decrease even when the charge / discharge cycle is repeated, and the current collector is wrinkled by charge / discharge. It was possible to suppress the occurrence.

Moreover, when the copper foil has a 0.2% proof stress of 250 N / mm ² or more after heat treatment at 200 to 400 ° C. for 30 minutes to 1.5 hours, the capacity decreases even if the charge / discharge cycle is repeated. It did not occur, and the generation of wrinkles on the current collector due to charge / discharge could be suppressed.

  Further, when a copper foil having a cross-sectional observation crystal grain size in the range of 20 to 2500 nm as measured by the SIM image is used for the current collector, the capacity does not decrease even when the charge / discharge cycle is repeated. It was possible to suppress the generation of wrinkles on the current collector due to the discharge.

  Comparative Examples 1 to 4 were foils having a small 0.2% yield strength at room temperature, and were softened by heating. The 0.2% yield strength was even smaller, and wrinkles were generated in the current collector after repeated charge and discharge.

  As described above, when a negative electrode current collector using the copper foil of the present invention and having a rust prevention treatment on at least one surface is used, it is possible to suppress the occurrence of deformation such as wrinkles in the current collector due to charge / discharge. Provided is a lithium ion secondary battery that can prevent a short circuit between a positive electrode and a negative electrode of a lithium ion secondary battery, has a long life and does not decrease in capacity even after repeated charge and discharge cycles, and can be miniaturized. be able to.

  Although the present embodiment describes the case where the active material is silicon, even when an active material mainly composed of silicon oxide, carbon, and tin is used, the current collector may be deformed such as wrinkles due to charge and discharge. Lithium ion that can suppress the generation, can prevent the short-circuit between the positive electrode and negative electrode of the lithium ion secondary battery, has a long life and does not decrease in capacity even after repeated charge and discharge cycles A secondary battery can be provided.

  It is also effective to use the copper foil of the present invention as a printed circuit board by laminating it with a rigid or flexible insulating substrate.

Claims (9)

A copper foil, which contains chlorine (Cl) and carbon (C) in a concentration of 10 ^{17 to} 5 × 10 ²⁰ atoms / cm ^{3, and} contains sulfur (S) and / or nitrogen (N) from 10 ¹⁵ to ¹⁵ A copper foil containing a concentration of 5 × 10 ¹⁹ atoms / cm ^{3 and} containing oxygen (O) at a concentration of 5 × 10 ²⁰ atoms / cm ³ or less.     The copper foil according to claim 1, wherein the copper foil has a minimum crystal grain size of 500 nm or less and a maximum of 2500 or less in a cross section in the thickness direction. The copper foil according to claim 1 or 2, wherein a 0.2% yield strength after heating the copper foil at 200 to 400 ° C is 250 N / mm ² or more.   The copper foil according to any one of claims 1 to 3, wherein the copper foil is an electrolytic copper foil or a rolled electrolytic copper foil obtained by further rolling the electrolytic copper foil.   An electrode of a secondary battery using the copper foil according to any one of claims 1 to 4 as a current collector, wherein at least one surface of the copper foil is subjected to a rust prevention treatment, and the rust prevention treatment is performed on the surface. An electrode of a secondary battery in which an active material layer is formed.   It is an electrode of the secondary battery which uses the copper foil in any one of Claims 1 thru | or 4 as a collector, Comprising: At least one surface of the said copper foil is roughened, The said roughened surface is rust-proofed An electrode of a secondary battery that is processed and has an active material layer formed on the surface that has been subjected to the antirust treatment.   The electrode of the secondary battery according to claim 5 or 6, wherein the active material layer constituting the electrode is formed of an active material containing carbon, silicon, tin, aluminum, magnesium, or calcium as a main component. .   A secondary battery incorporating the electrode according to claim 5.   A printed or flexible printed circuit board obtained by laminating the copper foil according to claim 1 with an insulating substrate.