JP5873711B2 - Copper foil, secondary battery electrode, secondary battery, and printed circuit board - Google Patents

Description

  The present invention relates to a copper foil used for a non-aqueous electrolyte secondary battery such as a printed circuit or a lithium ion secondary battery, the same electrode, and the same negative electrode current collector. In particular, the present invention relates to an electrolytic copper foil suitably used for a negative electrode current collector of a high capacity lithium ion secondary battery using a flexible printed circuit or an alloy negative electrode active material.

  Lithium ion secondary batteries comprising a positive electrode and a negative electrode current collector made of copper foil with smooth both surfaces are coated with carbon particles as a negative electrode active material layer, dried and further pressed, and a non-aqueous electrolyte. Used in mobile phones and notebook computers. As the negative electrode of the lithium ion secondary battery, a so-called “untreated electrolytic copper foil” manufactured by electrolytic deposition is used for rust prevention treatment.

  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.

  Recently, for the purpose of increasing the capacity of lithium ion secondary batteries, lithium ion secondary batteries using a metal negative electrode such as tin or silicon electrochemically alloyed with lithium during charging as a negative electrode active material have been proposed. (See Patent Document 2).

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).
Recently, a method has also been developed in which powdered silicon or a silicon compound is slurried with an imide-based binder and an organic solvent, applied onto a copper foil, dried, and pressed. (See Patent Document 4)

However, in such an electrode for a lithium ion secondary battery, for example, the silicon active material is said to expand in volume by about 2 to 4 times by electrochemically alloying lithium ions during charging. Shrinks during discharge. Such volume change of expansion and contraction accompanying charging and discharging is repeated.
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 at the current collector interface, or part of the coating film is detached. In addition, wrinkles may occur in the current collector. When charging and discharging are repeated many times, there is a problem that the current collector foil breaks in the worst case.

  When deformation such as wrinkles occurs in the current collector, there arises a problem that the positive electrode and the negative electrode are easily short-circuited. Further, when the current collector breaks, there arises a problem that stable battery performance cannot be maintained 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. A lithium ion secondary battery is formed using an electrolytic metal foil having a tensile strength of 400 N / mm ² or more or a breaking elongation of 7% or more and a product of tensile strength and breaking elongation of 2800 N / mm ² ·% or more. It is described to do. (Patent Document 5)

  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. Further, when charging / discharging of the electrode is repeated many times using a weak current collecting foil, there is a problem that the current collecting foil breaks in the worst case.
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 relates to a non-aqueous electrolyte secondary battery using a negative electrode in which an active material layer mainly composed of a metal active material mainly composed of tin or silicon and mainly having a high specific capacity is formed on a current collector foil. The purpose of the present invention is to provide a non-aqueous electrolyte secondary battery that is excellent in charge and discharge cycle efficiency, does not cause wrinkles in the current collector, and maintains stable performance for a long time without causing current collector breakage, It aims at providing the copper foil which can comprise the electrode for secondary batteries, and the electrical power collector of this electrode. It is another object of the present invention to provide an electrolytic copper foil for printed circuits, particularly for flexible printed circuits and fine pattern circuits.

According to the present invention, the copper foil has a purity of 99% by mass or more, and there is a non-uniform region having a copper density different from the surrounding copper density in the copper foil, and the size of the non-uniform region. Has a particle diameter of 1 to 10 nm, and the heterogeneous region is mainly composed of carbon, and at least one of chlorine, sulfur, and oxygen is provided.

  The non-uniform region having a particle size of 1 to 10 nm corresponds to the largest proportion of the total of impurity regions including other sizes, or the average size of all non-uniform regions The particle size is preferred.

  The particle size of the non-uniform region can be measured by small-angle X-ray scattering measurement, and the X-ray used for the small-angle X-ray scattering measurement is preferably a high energy type X-ray generated by using radiant light. .

Said copper foil has a copper purity of 95 to 99.999 wt%, tensile strength 500~1000N ^/ mm 2 at room temperature, 0.2% proof stress is a copper foil having a 350~800N / mm ² Is preferred.
The copper foil has a tensile strength of 275 to 800 N / mm ² after heat treatment at 300 to 350 ° C. for 1 hour, and a 0.2% proof stress after the heat treatment of 225 to 600 N / mm ^2. Preferably there is.

  The negative electrode of the present invention is a negative electrode using the copper foil of the present invention as a current collector, and at least one surface of the electrolytic copper foil is subjected to a roughening treatment and a rust prevention treatment as necessary. A negative electrode of a secondary battery in which an electrode-constituting active material layer is formed on the surface subjected to the rust prevention treatment.

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

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

  The copper foil is preferably an electrolytic copper foil or a copper foil obtained by rolling an electrolytic copper foil.

Since the copper foil of the present invention is mainly excellent in mechanical properties and its heat resistance, by using the copper foil as a negative electrode current collector of a non-aqueous electrolyte secondary battery, an active material layer associated with a charge / discharge reaction can be obtained. Non-aqueous electrolytes such as long-life lithium-ion secondary batteries that can withstand expansion and contraction and large stress on the current collector, do not cause deformation of the current collector, have little battery performance degradation, etc. A secondary battery can be realized.
The copper foil of the present invention is also suitable for printed circuit applications, particularly flexible printed circuits and fine pattern circuit applications, because of its high folding resistance due to its stress resistance performance and fine etching characteristics due to its fine grain structure. Can be used.

When a conventional carbon-based negative electrode constituent active material layer is formed on a current collector, a copper foil is prepared by making a paste composed of carbon as a negative electrode active material, polyvinylidene fluoride resin as a binder, and N-methylpyrrolidone as a solvent. Application and drying are performed on both sides of the (current collector).
In this case, drying is performed at a temperature of about 150 ° C. At a temperature around 150 ° C., the tensile strength, 0.2% proof stress, and elongation of the copper foil hardly change.
For example, it was manufactured using the electrolytic solution described in Patent Document 1 in which a copper sulfate-sulfuric acid electrolytic solution was added with a compound having a mercapto group, chloride ions, and a low molecular weight glue having a molecular weight of 10,000 or less and a high molecular weight polysaccharide. The electrolytic copper foil has a tensile strength at room temperature of 10 μm foil of 300 to 350 N / mm ² , but its performance hardly changes even when it is dried at a temperature of around 150 ° C.
Further, 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 current collector is not deformed or broken due to charging / discharging.

On the other hand, when using a metal-based active material such as a silicon-based material, a polyimide-based resin may be used for the binder in order to prevent expansion and shrinkage of the silicon-based active material during charge / discharge. In this case, the drying and curing temperature is higher than 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 foil is annealed and softened in the copper foil, and deformation of the foil is likely to occur due to expansion and contraction of the active material during charge and discharge.

  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. No deformation will 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.

  In the case of copper foil, having a large tensile 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 in Table 2 has a high tensile strength at room temperature, but after heating, it is annealed and softened, resulting in a foil having a small yield point.

  Here, the yield point is measured by a tensile test, but this point is not clear in the case of 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.

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 foil to break, 0.2% proof stress is required to be 250 N / mm ² or more, and elongation is required to be 4.5% or more.

In the copper foil, there are many non-uniform regions (hereinafter sometimes referred to as “precipitated phases”) having different densities from the surrounding copper density. From the scattering curve obtained as a result of the small-angle X-ray scattering measurement and the vector q (wave number vector: 4π sin θ / λ), the precipitated phase can be discriminated from the result of fitting analysis of the obtained scattering pattern. .
The copper foil of the present invention is a high-purity copper foil having 95 to 99.999% by mass, and the copper foil of the present invention has a large number of heterogeneous regions (precipitation phases) having different densities from the surroundings. Is recognized. The deposited phase of the copper foil of the present invention has a fine particle size of 1 to 10 nm assuming that the nanodomain shape is spherical.
In addition, the nano-domain-shaped precipitated phase having a fine particle size of 1 to 10 nm in the copper foil of the present invention occupies the largest proportion of the whole or has the average particle size of the whole.

Copper foil having a deposition phase of the fine particle diameter such as described above, as a result, it has a tensile strength 500~1000N / mm ² at room temperature, and good 0.2% proof stress of 350~800N / mm ² Have good mechanical properties.

Furthermore, the copper foil of the present invention has high heat resistance and softening resistance, and maintains a tensile strength of 275 to 800 N / mm ² even after heat treatment at 300 to 350 ° C. for 0.5 to 1.5 hours, and the heating. It has high mechanical and thermal properties that maintain a 0.2% yield strength after treatment of 225 to 600 N / mm ² .

There are cases where the X-rays used for the small-angle X-ray scattering measurement are high energy type X-rays generated by using synchrotron radiation, and normal, general and not particularly high energy may be generated. Often results in a measurement result that increases the proportion of large dimensional size. Small angle in small-angle X-ray scattering refers to scattering that appears in a scattering angle region of about 5 ° or less, and therefore requires more changes on the apparatus than general X-ray diffraction measurement, such as narrowing the direct beam. In small-angle scattering, when the scattering angle, which is the angle between the direct direction and the scattering direction, is expressed by 2θ, the size of the scattering vector q is q = 4π sin θ / λ (λ is the wavelength of the X-ray)
The small-angle scattering corresponds to about q = 0 to 0.3 ^-1 and is generally a measurement analysis method that can know a structure of 100 nm or less.

  A small-angle X-ray scattering pattern of the copper foil to be measured is measured, and on the other hand, the precipitation phase is assumed to be spherical, and further, the fitting analysis can be performed assuming the number of groups having a large proportion of the size. Thereby, the graph curve which shows a peak particle size with many existence ratios, those values, the ratio by the volume fraction with respect to the whole precipitation phase, and the value of the whole average particle diameter can be obtained. These values are the fine particle diameters detected by the copper foil of the present invention, and have favorable mechanical and thermal characteristics when there are many 1 to 10 nm precipitated phases.

  These precipitated phases are mainly present in the crystal grains. Ingredients such as carbon of organic additives that have been considered in the past have existed in the grain boundaries. In the present invention, since the additive compound component is arranged and present in the grains as a precipitated phase or matrix copper and a different phase component domain, simple grain boundary breakage due to mechanical stress and crystal fusion grain boundary expansion due to thermal stress are suppressed. It is thought that the pinning effect within a crystal grain is shown.

  The presence of these components such as carbon can be detected by a qualitative / semi-quantitative instrument analyzer such as EDS, EDX, or EPMA. When it is difficult to detect the presence of a light element such as carbon, it is possible to perform high-resolution and high-sensitivity analysis by EELS (Electron Energy-Loss Spectroscopy) of aberration correction STEM.

  Furthermore, the cross-sectional observation crystal grain size of these copper foils is in the range of 20 to 3500 nm. A clear image can be obtained by a scanning ion microscope (SIM) image taken out by FIB, and the particle diameter can be observed and confirmed.

  Moreover, the case where the copper foil of this invention is the electrolytic copper foil manufactured by the electrolytic deposition method, or the case where it is the copper foil which rolled the electrolytic copper foil is more desirable. This is because the above elements can be effectively taken into the copper foil by electrodeposition.

As a copper foil for a lithium-ion secondary battery negative electrode current collector, which is the main use of the copper foil of the present invention, a further required characteristic is a capacity retention rate when the battery charge / discharge cycle is repeated.
When the lithium ion secondary battery is repeatedly charged and discharged, the capacity retention rate gradually decreases. The smaller the decrease in the capacity maintenance rate, the higher the performance of the lithium ion secondary battery, and the longer it can be used, the customer is satisfied. On the other hand, if the battery deteriorates in a short time, the battery life is shortened, and the battery must be updated to a new one as soon as possible.
Factors affecting this property include deterioration of the negative electrode active material itself, formation of a film on the surface of the active material due to decomposition of the electrolytic solution, occurrence of cracks in the active material, or peeling between the active material and the copper foil.
Among these, what is considered to be caused by the copper foil is peeling between the electrode coating film and the active material and the copper foil.

As a cause of peeling between the coating film / active material and the copper foil, the surface roughness is one factor.
An appropriate surface roughness Rz as a current collector for a secondary battery is 0.8 to 2.8 μm. When Rz is less than 0.8 μm, there is no effect, and even when Rz is 2.8 μm or more, the effect is saturated, or the capacity retention rate during charge / discharge is deteriorated. Therefore, it is effective to form an active material layer by performing a rust prevention treatment on a roughened electrolytic copper foil (current collector) having a surface roughness Rz of 0.8 to 2.8 μm.

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.

  An electrolytic copper foil suitable for the negative electrode current collector of the lithium ion secondary battery of the present invention comprises an insoluble anode made of titanium coated with a white metal element or an oxide element thereof using a sulfuric acid-copper sulfate aqueous solution as an electrolyte, and the anode Copper is deposited on the surface of the cathode drum by supplying a direct current between both electrodes while supplying the electrolyte between the cathode cathode and a titanium cathode drum provided opposite to the cathode drum and rotating the cathode drum at a constant speed. The deposited copper is peeled off from the surface of the cathode drum and is continuously wound up.

  An electrolytic copper foil suitable for the negative electrode current collector of the lithium ion secondary battery of the present invention can be produced by adding a thiourea, a polymer polysaccharide, and a chloride ion to a sulfuric acid-copper sulfate electrolyte.

  In addition, among those skilled in the art, the surface of the side where the electrolytic copper foil is in contact with the surface of the cathode drum is referred to as a “glossy surface”, and the opposite surface is referred to as a “rough surface”. It is called “untreated electrolytic copper foil”.

In this case, the “untreated electrolytic copper foil” is an intermediate product, and is subjected to inorganic rust prevention treatment such as chromate treatment, organic rust prevention treatment such as benzotriazole, silane coupling agent treatment, etc., and lithium ion secondary battery Used as an electrolytic copper foil for a negative electrode current collector.
The inorganic rust-proofing treatment, organic rust-proofing treatment, and silane coupling agent treatment increase the adhesion strength with the active material, and play a role of preventing a decrease in capacity maintenance rate during charge / discharge of the battery.

Moreover, in order to make the surface roughness of the electrolytic copper foil surface Rz = 0.8 to 2.8 μm, the surface of the untreated electrolytic copper foil is roughened. 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 untreated electrolytic copper foil. As the plating method, an electrolytic plating method and an electroless plating method can be employed.

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 active material layer in the present invention is a substance that occludes / 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 in the present invention is preferably formed by slurrying the active material together with a binder and a solvent, coating, drying, and pressing.

  In the present invention, the current collector is preferably thin, and therefore is preferably a metal foil, particularly an electrolytic copper foil. The active material layer can be formed on one side or both sides of the current collector.

  In the active material layer in the present invention, lithium may be occluded or added 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.

  The non-aqueous electrolyte used in the lithium ion secondary battery of the present invention 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 the lithium ion secondary battery of the present invention is limited as long as the Li compound as a solute that develops ionic conductivity and the solvent that dissolves and retains it are not decomposed by the voltage at the time of charging, discharging or storing the battery. Can be used.

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.

  According to the present invention, a non-aqueous electrolyte secondary battery that can suppress wrinkle deformation or breakage of a current collector due to charge and discharge and maintain stable battery performance and electrode characteristics for a long period of time. Alternatively, a 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 1-3, Comparative Examples 1-3]

[Manufacture of untreated 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, ethylenethiourea was added as a thiourea, hydroxyethyl cellulose as a polymeric polysaccharide, and chloride ions were added so as to have the concentrations shown in Table 1 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 electrolytic solution, a noble metal oxide-coated titanium electrode for the anode, and a titanium rotating drum for the cathode, under an electrolysis condition (current density, liquid temperature) shown in Table 1, approximately 10 μm thick untreated Copper foil was manufactured by the electrolytic foil manufacturing method.

[Creation of negative electrode current collector]
For Examples 1 to 3 and Comparative Example 1 shown in Table 1, the surface of the untreated electrolytic copper foil 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 3 and Comparative Example 1, initially, an untreated copper foil of about 10 μm was prepared, and then copper burnt plating and capsule plating by electroplating were performed to a thickness of 12 μm. A roughened electrolytic copper foil was prepared and subjected to chromate treatment, and then a current collector was obtained. In addition, it conformed to the foil thickness and mass per unit area according to the IPC international standard.
On the other hand, for Comparative Examples 2 and 3, a 12 μm untreated copper foil was prepared, and then, copper chromate treatment and capsule plating were not performed, and only a chromate treatment was performed to obtain a current collector.
That is, the thicknesses of Examples 1 to 3 and Comparative Examples 1 to 3 were adjusted so as to have a mass thickness equivalent to 12 μm when they were current collectors.
The conditions for the granular powder plating for roughening the copper foil surface, the smooth copper plating (capsule plating), and the conditions for the chromate treatment are as follows.
Granular 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

Dense copper plating (cover 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

Small-angle X-ray scattering measurement of the manufactured current collector copper foil was performed under the following conditions.
Synchrotron X-ray scattering wavelength 0.08nm
Beam diameter length 0.2mm, width 0.6mm
Small angle camera length approx. 1700mm
Small-angle detector Rigaku R-AXIS VII (IP),
Pixel size: 100 μm square Among the scattering vectors obtained from the measurement of the six types of copper foils of Examples 1 to 3 and Comparative Examples 1 to 3, on the small angle side, the scattering pattern determined to be unique to the precipitated phase, Fitting analysis (assuming the precipitate is spherical and analyzing the distribution of particle size), the size of the precipitate present in each copper foil, the average value of the entire particle size and the distribution of each peak size Table 2 shows the particle diameters where the peak of (2) is shown (indicated by rounded numbers in Table 2). In addition, Table 2 shows the tensile strength, 0.2% proof stress, and elongation of each copper foil.
In addition, about the copper foil used for the comparative examples 2 and 3, the scattering pattern considered to be based on a precipitate on the small angle side was not recognized by the scattering vector obtained from the X-ray measurement.

  The tensile strength, 0.2% proof stress, and elongation were measured using a tensile tester (Model 1122 manufactured by Instron).

  Direct observation by the STEM image of the produced copper foil of Table 1 and qualitative analysis by EDX or EELS of the observed precipitated phase (domain) were performed. In any of the precipitated phases, the amount of detected copper was smaller than that of the surrounding phase copper, and carbon C was mainly detected. These detection elements are shown in Table 3, and the approximate value of the crystal grain size by observation of the FIB cross-section SIM image is also shown. The detection elements other than C in the precipitated phase differed in sub-detection elements depending on the domain, and chlorine, sulfur, or oxygen was detected. Nitrogen has low power in qualitative analysis, and its presence was confirmed by SIMS. Moreover, it was confirmed that the copper purity of each copper foil was 99% or more by ICP emission spectroscopic analysis.

[Create negative electrode]
A mixture of silicon having an average particle diameter of 0.15 μm and silicon alloy powder (Si purity of about 90%) is used as the negative electrode active material particles, and the negative electrode active material particles and the binder are 85:15 using polyimide as a binder. In addition to N-methyl-2-pyrrolidone so as to be a mass ratio of these, 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 25 μm.

Then, after rolling to an electrode thickness of 20 μm using a rolling roller, this was sintered at each temperature shown in Table 1 for 1 hour in a nitrogen atmosphere to prepare a negative electrode.

[Production of counter electrode and reference electrode for triode cell]
To test and evaluate the charge / discharge characteristics of the negative electrode in a triode cell, a lithium foil was bonded to a stainless mesh mesh on a counter electrode and a reference electrode.

[Non-aqueous electrolyte]
In preparing the non-aqueous electrolyte, a mixed solvent in which ethylene carbonate and diethylene carbonate were mixed at a volume ratio of 3: 7 was used as a main component, and LiPF ₆ was dissolved to a concentration of 1 mol / liter. A non-aqueous electrolyte (power light) manufactured by Ube Industries was used.

[Evaluation of battery charge / discharge characteristics]
The above-mentioned negative electrode (test electrode), counter electrode, reference electrode, and triode cell using a non-aqueous electrolyte are assembled and wired in a non-aqueous environment glow box in an argon atmosphere, sealed in a sealed container, and then in the atmosphere. The charge / discharge characteristic test was conducted.

  In the test, after charging and discharging at a 0.1C test rate for the first time, 50 charge / discharge cycle tests at 0.2C were repeated. Charging was carried out at CC (constant current) up to 0.02V with respect to the standard unipolar potential of Li, and thereafter the CV (still at constant potential) current was reduced by 0.05C to terminate charging. Discharge was performed to 1.5V (Li reference) at CC. 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 6 and Comparative Examples 1 and 2 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, when the copper foil of the present invention was used as a current collector, it was possible to suppress wrinkles from occurring in the current collector due to charge and discharge. Further, the capacity does not decrease even when the charge / discharge cycle is repeated.

This copper foil with a deposited domain of the present invention represents an intensity 500~1000N / mm ² tensile at room temperature, and shows a 0.2% proof stress 350~800N / mm ^2, after heat treatment of 300 to 350 ° C. It has a tensile strength of 275 to 800 N / mm ² and exhibits high mechanical and heat resistance characteristics such as 0.2% proof stress 225 to 600 N / mm ² after the heat treatment. It was possible to suppress the occurrence of wrinkles. Further, the capacity does not decrease even when the charge / discharge cycle is repeated.

  Moreover, although many precipitation domains exist in the copper foil matrix of Comparative Example 1, since the size is a large particle size exceeding 10 nm, the pinning strength maintaining effect due to the precipitation domains as a whole is inferior. It seems to be a thing. In Comparative Examples 2 and 3, it was considered that the presence of the precipitation domain was almost not observed, and therefore the mechanical and thermal characteristics were small. Therefore, when charging and discharging were repeated, the current collector was wrinkled.

    As described above, the copper foil of the present invention having a precipitate domain in the copper foil matrix and the recognized domain size of 1 to 10 nm from the scattering vector analysis obtained by the small-angle X-ray scattering measurement is high. Because it has high strength, high yield strength and high heat resistance, use a negative electrode current collector with rust prevention treatment on at least one surface of the copper foil, or use copper foil with rust prevention treatment by roughening at least one surface And, it is possible to suppress the occurrence of deformation such as wrinkles in the current collector due to charging / discharging, to prevent a short circuit between the positive electrode and the negative electrode of the lithium ion secondary battery, It is possible to provide a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery that has a long life and does not deteriorate and can be miniaturized.

  In this example, the active material is a mixture of silicon or a silicon alloy. However, even when an active material mainly composed of silicon alone, silicon oxide, carbon, or tin is used, the active material is collected by charging / discharging. Can suppress the deformation of the electric body such as wrinkles, can prevent the short-circuit between the positive and negative electrodes of the lithium ion secondary battery, and has a long life that does not cause a decrease in capacity even after repeated charge / discharge cycles The non-aqueous electrolyte secondary battery including the lithium ion secondary battery can be provided.

Claims (9)

A copper foil having a purity of 99% by mass or more, wherein a non-uniform region having a copper density different from the surrounding copper density is present in the copper foil, and the size of the non-uniform region has a particle size of 1 to 10 nm. The non-uniform region is a copper foil mainly composed of carbon and containing at least one of chlorine, sulfur, and oxygen .   The non-uniform region having a particle size of 1 to 10 nm corresponds to the largest proportion of the total of impurity regions including other sizes, or the average size of all non-uniform regions The copper foil according to claim 1, which has a particle size.   The particle size of the non-uniform region is measured by small-angle X-ray scattering measurement, and the X-ray used for the small-angle X-ray scattering measurement is a high energy type X-ray generated by using radiant light. The described copper foil. The copper foil has a tensile strength after heat treatment at 300 to 350 ° C. of 275 to 800 N / mm ² and a 0.2% proof stress after the heat treatment of 225 to 600 N / mm ² . The copper foil in any one. An electrode of a secondary battery using the copper foil according to any one of claims 1 to 4 as a current collector, wherein the copper foil is an electrolytic copper foil,
It has a rust prevention layer on at least one surface of the electrolytic copper foil,
Having an electrode-constituting active material layer on the surface of the antirust treatment layer,
Secondary battery electrode. An electrode of a secondary battery using the copper foil according to any one of claims 1 to 4 as a current collector , wherein the copper foil is an electrolytic copper foil,
It has a roughening treatment layer and a rust prevention layer on at least one surface of the electrolytic copper foil ,
The surface of rustproof treated layer having the electrodes constituting the active material layer,
Secondary battery electrode. The active material layer, carbon, silicon, tin, aluminum, having an active material mainly composed of either magnesium or calcium, the electrode of the secondary battery according to claim 5 or 6. Secondary battery having an electrode according to any one of claims 1 to 7. The copper foil according to claim 1, formed by laminating an insulating substrate, a printed circuit board or a flexible printed circuit board.