TW201443290A - Electrolytic copper foil, battery current collector comprising said electrolytic copper foil, electrode obtained using said current collector for secondary battery, and secondary battery obtained using said electrode - Google Patents

Abstract

An electrolytic copper foil is provided in which the tensile strength measured at ordinary temperature after a 300 C1 hour heat treatment is 500 MPa or higher. Also provided is an electrolytic copper foil which, when laminated to a polyimide film, gives a printed wiring board having excellent mechanical strength. Furthermore provided is a copper alloy foil which, when used as a current collector (copper foil) in a lithium-ion secondary battery employing an active material based on an Si or Sn alloy, retains adhesion to the active material with the aid of a polyimide binder and suffers neither deformation nor breakage. The electrolytic copper foils contain tungsten in an amount of 0.06-0.5 wt%, with the remainder comprising copper. The electrolytic copper foils have a tensile strength measured at ordinary temperature after a 300 C1 hour heat treatment of 500 MPa or higher. A secondary battery is further provided in which either of the electrolytic copper foils is used as a current collector.

Description

Electrolytic copper foil, battery current collector using the electrolytic copper foil, secondary battery electrode using the current collector, and secondary battery using the same

The present invention relates to an electrolytic copper foil having an electrical resolution surface having a low roughness and a high mechanical strength, and it is difficult to change the mechanical strength even when heated at a high temperature.

The present invention relates to a secondary battery in which the electrodeposited copper foil is used as a current collector for a secondary battery, and an active material is stacked on the current collector to be an electrode for a secondary battery, and the electrode is assembled.

The electrolytic copper foil of the present invention can be suitably used for a rigid printed wiring board, a flexible printed wiring board, an electromagnetic shielding material, or the like using the electrolytic copper foil as a conductive material.

In addition, in the present specification, when it is not necessary to distinguish between an electrolytic copper foil and an electrolytic copper alloy foil (a foil containing an alloy of copper and a third metal in a foil, and a foil containing a third metal in a solid solution state in the foil), it is expressed as "electrolysis". Copper foil, in addition, mechanical strength refers to tensile strength.

Copper foil has been used in various fields such as rigid printed wiring boards, flexible printed wiring boards, electromagnetic shielding materials, and battery collectors.

A hard disk (hereinafter referred to as "HDD") in the field of printed circuit boards (flexible circuit boards, hereinafter referred to as "FPC") coated with polyimide film in these fields. Suspension materials, or automatic tape-bonding (hereinafter referred to as "TAB") materials require an increase in the strength of the copper foil.

Suspension mounted on the HDD With the development of the high capacity of the HDD, most of the wire-type suspensions that have been used in the past have been converted into a wiring-integrated type that can ensure the buoyancy and positional accuracy of a stable floating head with respect to a memory medium, that is, a disk. Suspension.

The wiring-integrated suspension is classified into the following three types.

a FSA (flex suspension assembly) suspension, which is used to process a flexible printed circuit board and adhere it with an adhesive; b. CIS (circuit integrated suspension) suspension, After the shape processing of the precursor of the polyimine resin, ie, proline, the oxime is imidized, and then electroplating is performed on the obtained polyimine to form a router; c. TSA ( A trace suspension assembly is a suspension in which a laminate composed of a stainless foil-polyimine resin-copper foil is processed into a predetermined shape by etching.

Since the TSA suspension is used to laminate a copper alloy foil having high strength, the flying wire can be easily formed, and the shape processing has a high degree of freedom, is inexpensive, and has high dimensional accuracy, and is therefore widely used.

The laminated system formed by the TSA method is made of a material having a thickness of about 12 to 30 μm, a thickness of a polyimide resin layer of about 5 to 20 μm, and a thickness of a copper foil of about 7 to 14 μm. .

In the production of a laminate, a polyimide resin solution is first applied onto a stainless foil as a substrate. After coating, remove the solvent by preheating, and then re-solidify A heat treatment is applied to form a quinone imine. Then, a copper alloy foil is superposed on the polyimide layer of the yttrium imidized, and is subjected to heat-bonding at a temperature of about 300 ° C and laminated to form a layer composed of a stainless layer-polyimine layer-copper alloy layer. The laminate.

When heated at about 300 ° C, the stainless foil hardly changes in size. However, when the conventional electrolytic copper foil is used, the electrolytic copper foil is annealed at a temperature of about 300 ° C, recrystallized and softened, resulting in dimensional change. Therefore, the laminated body is warped after lamination, and the dimensional accuracy of the product is lowered.

In order to prevent the laminate from being lifted after lamination, it is required to provide a copper alloy foil having a dimensional change as small as possible during heating.

In addition, the TAB material, like the HDD suspension material, requires high strength of the copper foil and low roughness of the foil surface.

In the TAB product, a plurality of terminals of the IC chip are directly combined with inner leads (flying wires) disposed at the device holes located at almost the center of the product. This combination is carried out by using a bonding device by applying a fixed bonding pressure by instantaneous energization heating. At this time, the inner lead obtained by etching the electrolytic copper foil may have a problem that it is stretched due to the bonding pressure, resulting in elongation.

Further, if the strength of the electrolytic copper foil is too low, there is a problem in that the internal lead is slack due to plastic deformation, and even if it is severe, it is broken.

Therefore, in order to make the line width of the inner lead thinner, the electrolytic copper foil required for use in the industry has a rough surface which is subjected to a low roughening treatment and has high strength.

At this time, the copper foil must have high strength in a normal state (normal temperature, normal pressure state), and still have high strength after heating. For TAB use, a 2- or 3-layer FPC in which copper foil is bonded to polyimine is used. 3 layer FPC, when When the polyimide is bonded to a copper foil, an epoxy-based adhesive is used, and the bonding is carried out at a temperature of about 180 °C. Further, when a two-layer FPC having a polyimide-based adhesive is used, the bonding is carried out at a temperature of about 300 °C.

Even if the electrolytic copper foil is mechanically strong in a normal state, it is meaningless if the copper foil softens when it is bonded to the polyimide. In the past, the high-strength electrolytic copper foil has a large mechanical strength under normal conditions, and the mechanical strength hardly changes even when heated at about 180 ° C. However, when heated at about 300 ° C, annealing occurs and recrystallization is performed. Therefore, it will soften rapidly and the mechanical strength will decrease. This copper foil is not suitable for TAB use.

Further, the copper foil is also used as a current collector for a battery such as a lithium ion secondary battery. A lithium ion secondary battery basically consists of a positive electrode, a negative electrode, and an electrolyte. A negative electrode is formed by coating a surface of a copper foil used as a current collector with a negative electrode active material layer.

As a method of forming the negative electrode, a slurry in which a negative electrode active material and a binder resin (added to bond the active material to the copper foil substrate) is dissolved in a solvent is applied to the copper foil substrate to form a binder resin. A method of forming by pressing after drying at a temperature higher than the hardening temperature.

As a binder resin, polyvinylidene fluoride (PVDF) and styrene-butadiene rubber (SBR) are widely used in the industry.

In recent years, with the increase in capacity of batteries, active materials composed of ruthenium, tin, and ruthenium alloy materials having a high theoretical capacity have attracted attention, and their volume expansion ratio is very high due to insertion and desorption of lithium during charge and discharge. Large, the strength of the above binder resin is insufficient. Therefore, it is preferable in the industry to use a polyimide resin having a high bonding strength with a copper substrate. However, the polyimide resin and the above adhesive Unlike the resin, the hardening temperature is very high and reaches about 300 ° C. Therefore, it is required that the negative electrode current collector (copper foil) can withstand the heating condition.

As described above, in the FPC field and the secondary battery field, a polyimide resin having a very high curing temperature and a temperature of about 300 ° C is used as a binder, and therefore it is required that the copper foil can withstand the heating condition.

An electrolytic solution containing copper sulfate and sulfuric acid is used as an electrolytic solution of the electrolytic copper foil, and various additives are added to the plating bath for the glossing and smoothing of the surface of the copper foil, and the stress reduction of the copper foil. When the additive is not used, the surface morphology and mechanical properties required for the copper foil cannot be obtained, and therefore the importance of the additive is very high. In particular, the copper sulfate plating bath is a simple acid bath, so that the uniform plating property is poor, and it is difficult to produce a desired electrolytic copper foil without an additive. As an additive used in a copper sulfate plating bath, a brightener such as a chloride ion, a polyoxyethylene type surfactant, a smoothing agent, an organic sulfide, a gel, gelatin or the like is proposed and used.

If chlorine or an additive is not added to the copper sulfate plating bath, the electroplating will concentrate on the high current portion (close to the anode, the cathode end, the front end of the sharp object, etc.) of the easy-flowing electrical, and become a so-called "burnt state" ( The plating surface is more convex and concave)". For this reason, it is common to add chloride ions when electroplating copper sulfate.

However, if chlorine ions are generally present in the electrolytic solution, it is difficult to mix a specific metal into the copper foil to change the characteristics of the copper foil. In other words, in the electrolyte solution in which chloride ions are not present, other metals can be mixed in the copper foil, and the characteristics of the copper foil can be changed by mixing other metals (alloying). However, when chlorine ions are added to the electrolyte solution, it is difficult for other metals to be mixed into the copper. In foil, it is extremely difficult to change the characteristics of copper foil by other metals.

Further, for example, Patent Documents 1 and 2 disclose that electrolytic solution is used for adding tungsten to a sulfuric acid-copper sulfate electrolyte solution, and further adding a gel and a chloride ion. The method of copper foil, the literature says, the effect is that the thermal elongation at 180 ° C is 3% or more, the roughness of the rough surface is large, and the copper foil having less pinholes is produced.

Then, the inventors of the present invention repeatedly performed the experiment of adding tungsten to a sulfuric acid-copper sulfate electrolyte solution and adding a gel and a chloride ion to prepare a heating at 180 ° C for the purpose of the electrolytic copper foil described in Patent Document 1. A copper foil having an elongation of 3% or more, a rough surface roughness, and a small occurrence of pinholes.

However, after the copper foil was subjected to heat treatment at 300 ° C for 1 hour, it was found that mechanical strength could not be maintained. Then, after analyzing the copper foil, the result was that tungsten was not co-deposited in the electrodeposited copper.

That is, according to the methods of Patent Documents 1 and 2, electrolysis is carried out by adding tungsten to a sulfuric acid-copper sulfate electrolyte solution, and further adding an electrolyte of 10 mg/L or less and a chloride ion of 20 to 100 mg/L, thereby performing copper plating. Tungsten was not precipitated in the middle, and as a result, it was impossible to produce an electrolytic copper foil which maintained high mechanical strength even when heated at 300 °C.

As described above, the electrolytic copper foil is produced by adding chlorine and an organic compound as an additive to an electrolytic solution containing copper sulfate and sulfuric acid.

Organic additives generally have an effect of suppressing crystal growth, and are therefore generally considered to be ingested into a grain interface.

At this time, the more the amount of the organic additive that ingests the grain interface, the more the mechanical strength tends to increase (Non-Patent Document 1: Shiga Chapter 2, Metal Surface Technology, Vol. 31, No. 10, p. 573 (1980)).

As described in Non-Patent Document 1, the organic additive that ingests the electrolytic copper foil can improve the mechanical strength of the copper foil. It can be considered that the organic additive is mainly taken into the grain interface and the mechanical strength is increased at normal temperature. However, when the electrolytic copper foil of the organic additive is heated at a high temperature of 300 ° C or higher, the machine The mechanical strength will decrease. It is generally assumed that the organic additive will decompose by heating, eventually resulting in a decrease in mechanical strength.

On the other hand, as a copper foil which satisfies the above requirements, a rolled copper alloy foil is used in the industry. The rolled copper alloy foil is less likely to be annealed at a temperature of about 300 ° C, and the dimensional change during heating is small, and the mechanical strength change is small.

However, the price of rolled copper foil is higher than that of electrolytic copper foil, and it is difficult to meet the requirements of width, thickness, and the like.

Then, the inventors of the present invention have an electrolytic copper foil having a low roughness and excellent mechanical strength as a surface to be bonded to a polyimide resin substrate, and an electrolytic solution suitable for use as a binder resin for a polyimide resin. Copper foil, try to add various metals to the copper foil to improve its heat resistance.

However, it is extremely difficult to ingest a metal which can improve the heat resistance of the copper foil into the electrolytic copper foil. That is, a metal which improves the heat resistance of a copper foil is extremely difficult to ingest a metal in a copper foil.

[Prior Art Literature]

[Patent Literature]

[Patent Document 1] Japanese Patent No. 3238278

[Patent Document 2] Japanese Patent Laid-Open No. Hei 9-67693

[Private Document 3] International Publication No. 2013/018773

[Non-patent literature]

[Non-Patent Document 1] Shiga Chapter 2, Metal Surface Technology, Vol31, No. 10, p573 (1980)

After intensive research, the present inventors have succeeded in developing an electrolytic copper foil having tungsten (W) and having a tensile strength of 450 MPa or more measured at room temperature after heat treatment at 300 ° C for 1 hour (refer to Patent Document 3). And continue to study repeatedly, and finally successfully developed a tungsten content of 0.06wt% ~ 0.5wt%, chlorine (Cl) content of 0.001wt% ~ 0.07wt%, and 300 ° C × 1 hour heat treatment after the tensile test Electrolytic copper foil having a strength of 500 MPa or more.

Further, the present inventors have succeeded in developing an electrolytic copper foil which can be used, for example, as an HDD suspension material, a TAB material, or as an active material which repeatedly expands and contracts greatly in an active material such as Si or a Sn alloy. The current collector (copper foil) of the adhesive does not deform.

An object of the present invention is to provide an electrolytic copper foil which has a tensile strength measured at room temperature after heat treatment at 300 ° C for 1 hour of 500 MPa or more.

Further, an object of the present invention is to provide an electrolytic copper foil excellent in mechanical strength in the field of a printed wiring board to which a polyimide film is bonded.

Further, an object of the present invention is to provide a copper foil which is used for a large expansion and contraction of an active material of Si or a Sn alloy in a lithium ion secondary battery using an active material of Si or a Sn alloy, by polyimine The adhesive maintains the adhesion of the current collector (copper foil) to the active material, and the current collector (copper foil) does not deform or break.

The electrolytic copper foil of the present invention has a tungsten content of 0.06 wt% or more.

More preferably, the electrolytic copper foil of the present invention has a tungsten content of from 0.06 wt% to 0.5 wt%.

In the electrolytic copper foil of the present invention, the tungsten content is from 0.06 wt% to 0.5 wt%, and the chlorine content is from 0.001 wt% to 0.07 wt%.

Preferably, all or part of the above tungsten is taken up as an oxide.

Further, according to the present invention, there is provided an electrolytic copper foil containing tungsten, the remainder being substantially composed of copper. In addition, the above-mentioned "the remaining portion is substantially composed of copper" means that the copper is contained in an inevitable impurity such as a raw material or a trace amount of an additive such as an electrolytic foil-forming process.

In the electrolytic copper foil of the present invention, the tungsten content is 0.06 wt% to 0.5 wt%, and the tensile strength measured at room temperature after heat treatment at 300 ° C for 1 hour is 500 MPa or more.

Further, the electrolytic copper foil of the present invention has a tungsten content of 0.06 wt% to 0.5 wt%, a chlorine content of 0.001 wt% to 0.07 wt%, and a tensile strength of 500 MPa or more measured at room temperature after heat treatment at 300 ° C for 1 hour.

The current collector for a secondary battery of the present invention is characterized by using the electrolytic copper foil according to any one of the above.

Further, the electrode for a secondary battery of the present invention is characterized in that the electrodeposited copper foil according to any one of the above-mentioned items is used as a current collector for a secondary battery, and an active material is stacked on the surface thereof.

The secondary battery of the present invention is a secondary battery using the above electrode for a secondary battery.

According to the present invention, an electrolytic copper foil can be provided, which is a normal machine The mechanical strength is large, and it is difficult to cause thermal deterioration after heating at 300 ° C or higher.

The electrolytic copper foil of the present invention contains tungsten, and the remainder is copper electrolytic copper foil.

The tungsten content in the above electrolytic copper foil is 0.06 wt% or more, more preferably 0.06 wt% to 0.5 wt%.

The reason why the tungsten content is set to 0.06 wt% or more is that the tensile strength measured at room temperature after heat treatment at 300 ° C for 1 hour can be improved as compared with the copper foil having a content of less than 0.06 wt %, and can be used as a battery. The current collector can extend the cycle life of the battery.

The reason why the amount of addition of tungsten is preferably 0.5% by weight or less is that even if the amount added is more than 0.5% by weight, the effect is saturated, and the effect of improving physical properties is hardly observed. In addition, it also causes a decrease in electrical conductivity, which is not preferable.

The inventors of the present invention repeated various experiments in order to produce an electrolytic copper foil containing W. As a result, in the electrolyte containing chlorine ions, even if a large amount of tungsten is added to the liquid, tungsten is not taken into the copper foil, and of course, the normal temperature of the copper foil made of the electrolyte and the foil after heating are used. The mechanical strength has not improved.

However, it has been recognized that even if a chloride ion is added to the electrolyte, if a thiourea compound is added to the liquid, the tungsten is taken up in the foil according to the foil-forming conditions.

Further, in the electrolytic copper foil of the present invention, the tungsten content is from 0.06 wt% to 0.5 wt%, and the chlorine content is from 0.001 wt% to 0.07 wt%.

The reason why the chlorine content is 0.001% by weight or more is that if the content is less than 0.001% by weight, the surface of the copper foil loses surface smoothness. Further, the reason why the chlorine content is set to 0.07 wt% or less is that if the content is more than 0.07 wt%, the electrolytic copper foil produced tends to have a tendency to decrease in initial strength, and since the initial strength is lowered, the strength after heating is also increased. reduce.

Based on the above findings, an electrolytic copper foil was produced under the following conditions, and an electrolytic copper foil excellent in heat resistance was successfully produced.

Basic electrolytic bath composition:

Cu=70g/L

H ₂ SO ₄ = 50g / L

Electrolysis conditions:

Current density = 40A/dm ²

Liquid temperature = 45 ° C

The additive added to the sulfuric acid-copper sulfate-based copper electrolyte is as follows.

Additive A: Thiourea compound = 2~20mg/L

Additive B: Tungsten salt (as tungsten) = 150~1,000mg/L

Additive C: chloride ion = 5~70mg/L

Further, the above-mentioned additive B is intended to mean "a tungsten metal equivalent to a tungsten salt of 150 to 1,000 mg/L" (the same applies hereinafter).

Additive A: A thiourea compound means an organic compound having the following structure.

>N-C(=S)-N<

Examples of the thiourea compound include thiourea, N, N-diethyl Thiourea, tetramethylthiourea, and ethylene thiourea. However, these are merely illustrative of the substances used in the following examples, and as long as they have the characteristics of the above-described structure, the same effects can be exerted, and any compound can be used.

Additive B: The tungsten salt is dissolved in an electrolytic solution containing copper sulfate and sulfuric acid, and examples thereof include sodium tungstate, ammonium tungstate, and potassium tungstate.

Additive C: When chloride ion is added, it is selected from a compound dissolved in an electrolytic solution containing copper sulfate and sulfuric acid. Examples thereof include hydrochloric acid, sodium chloride, and potassium chloride.

The reason why a thiourea compound is used as an organic additive is that a thiourea compound having a [=S] structure preferentially adsorbs to an adsorption layer of copper to form an organic molecule, and a tungsten oxide is adsorbed on the adsorption layer, whereby tungsten is combined with The thiourea compound is taken together in the foil.

Tungsten exists as an oxide in an acidic solution. However, when copper electrolysis is performed using an electrolyte containing chlorine, chloride ions cover the precipitation surface of copper, so tungsten oxide is not adsorbed onto copper, and tungsten is not ingested. In the foil. When a thiourea compound is added to the electrolytic solution, the [=S] structure is preferentially adsorbed onto the copper than the chloride ion, and an adsorption layer of an organic molecule is formed on the copper. It is generally assumed that tungsten is adsorbed onto the adsorption layer by tungsten oxide, and the tungsten is taken into the foil together with the thiourea compound.

As described above, the electrolytic copper foil of the present invention is formed by electrolysis of an electrolytic solution containing tungsten, a thiourea compound, and chlorine in a sulfuric acid-copper sulfate electrolyte. It is generally believed that when copper is electrolyzed in such a sulfuric acid-sulfur urea-containing compound and chlorine-containing sulfuric acid-copper sulfate electrolyte, the tungsten oxide is adsorbed together with the thiourea compound into the grain interface of copper, and the crystal nucleus The growth is suppressed, the crystal grains become fine (low roughness), and electrolytic copper having high mechanical strength under normal conditions is formed. Foil.

Therefore, it is generally considered that even if the electrolytic copper foil containing tungsten is heated at a high temperature of about 300 ° C, the tungsten oxide stays in the grain interface to prevent the fine crystal of copper from recrystallizing due to heat, and the crystal is changed. Coarse.

The electrolytic copper foil of the present invention has a low roughness and a low mechanical strength even after being heated at a high temperature of about 300 ° C. The electrolytic copper foil which has been previously produced by using a sulfuric acid-copper sulfate electrolyte using an organic additive Excellent features not available.

It is considered that the thiourea compound added to the sulfuric acid-copper sulfate electrolyte solution forms a complex compound with the metal element and chlorine in the electrolytic solution.

When tungsten is not added, the metal element added to the electrolytic solution for producing the electrolytic copper foil is copper. Therefore, a copper-thiourea compound is formed in an electrolyte containing copper sulfate and sulfuric acid. After the electrolytic copper foil is formed by electrolysis of copper of the electrolytic solution, the copper-thiourea compound is adsorbed to the grain interface, the growth of the crystal nucleus is suppressed, and the crystal grains become fine, and the electrolysis is performed under normal conditions. Copper foil.

However, it is generally considered that in the copper foil, the substance present in the grain interface is a copper-thiourea compound, copper is crystallized or absorbed by the internal copper crystal, and the substance present in the grain interface is only a thiourea. The compound is thus decomposed when exposed to a high temperature of about 300 ° C, and the final mechanical strength is lowered.

It is considered that the tensile strength is remarkably lowered when heated at a high temperature of about 300 ° C. The reason that the compound existing in the grain interface is an organic compound as described above, and the organic compound is liable to be heated by heating at about 300 ° C. Decomposed, so the mechanical strength will decrease.

According to the methods disclosed in Patent Documents 1 and 2, electrolysis is carried out using different organic compounds to produce an electrolytic copper foil, but all of them are made of a sulfuric acid-copper sulfate electrolyte containing an organic additive and chlorine, and The grain interface adsorbed on the electrolytic copper foil is an organic compound component. Therefore, when the electrolytic copper foil is exposed to a high temperature of 300 ° C or higher, the mechanical strength is remarkably lowered. The reason is generally that the compounds adsorbed into the grain interface are An organic compound that is easily decomposed under heating at a temperature of 300 ° C or higher.

However, in the present invention, copper electrolysis is carried out by adding an electrolyte solution containing tungsten, a thiourea compound, and chlorine to an electrolytic solution containing copper sulfate and sulfuric acid to form a copper alloy foil, so that the tungsten oxide and the thiourea are different. The compounds are adsorbed together onto the copper. By the adsorbed tungsten oxide and the thiourea compound, the growth of the crystal nucleus is suppressed, the crystal grains become fine, and the electrolytic copper foil having a high mechanical strength in a normal state is formed.

Thus, it is considered that in the electrolytic copper foil of the present invention, tungsten oxide and thiourea compounds are present in the grain interface, and therefore, unlike the copper-thiourea compound, the tungsten oxide is not crystallized by the inner copper. In combination with or absorption, tungsten oxide and thiourea compounds will continue to reside in the grain interface. Therefore, even when exposed to a high temperature of about 300 ° C, the oxide of the tungsten metal stays in the grain interface, preventing the fine crystal of copper from being recrystallized by heat, and the crystal becomes coarse.

When an electrolyte solution to which chloride ions are added is used as described above, it is extremely difficult to actually take tungsten into the copper foil. However, in the present invention, tungsten is successfully taken up into the copper foil by the addition of a thiourea compound.

The amount of the thiourea compound to be added is set to 2 mg/L to 20 mg/L. The reason is that if it is less than 2 mg/L, tungsten cannot be taken into the copper foil by a predetermined amount, and the tensile strength after heat treatment at 300 ° C for 1 hour is lowered, and if the amount is more than 20 mg / L, the state of the foil is lifted. (Curling) is enhanced, so the amount of addition is preferably in the range of 2 mg/L to 20 mg/L.

The amount of chloride ion added is 5~70mg/L. When the amount of chlorine ions added is less than 5 mg/L, there is a problem that the surface roughness is remarkably increased (the smoothness of the surface is impaired), which is not preferable. If the amount of chlorine ions added exceeds 70 mg/L, the foil is used. The initial strength is lowered, so it is not preferred. Therefore, the amount of chlorine ions added is preferably in the range of 5 to 70 mg/L, more preferably 10 to 30 mg/L.

A copper sulfate solution containing tungsten, a thiourea compound, and a chloride ion added in the above-mentioned predetermined amount is used as an electrolytic solution, titanium is coated with a noble metal oxide as an anode, and a titanium drum is used as a cathode at a current density of 30 to 100 A/dm. ^2. Electrolytic treatment is carried out under the conditions of a liquid temperature of 30 to 70 ° C to prepare an electrolytic copper foil.

When a polyimide polyimide binder is used, the current collector (copper foil) constituting the anode current collector of the lithium ion secondary battery usually must be capable of withstanding heat treatment at 300 ° C for 1 hour. In other words, a surface of a current collector for a lithium ion secondary battery is applied to a mixture of an active material, a conductive material, and a binder, and a solvent or the like is added to prepare a paste-form active material composition, which is subjected to a drying process to produce a lithium ion. The electrode of the secondary battery. In the drying process, heat treatment at 300 ° C for 1 hour must be performed. The copper foil which can withstand the heating conditions of the drying process and can withstand the expansion and contraction caused by the charge and discharge cycle of the active material preferably has a tensile strength of 500 MPa or more measured at room temperature after heat treatment at 300 ° C for 1 hour. Conditional performance.

In addition, active substances such as Si and Sn are compared with active substances such as carbon. The electron conductivity is poor. If the conductivity of the active material is poor, the internal resistance of the electrode is increased, and the cycle characteristics are deteriorated.

The tungsten-containing electrolytic copper foil of the present invention satisfies the various characteristics required for the above-mentioned secondary battery collector. Therefore, by using the electrolytic copper foil as a current collector, an electrode is formed by laminating bismuth, antimony, tin or the alloy compound or the active material as a main component in the current collector, and the electrode is incorporated. The electrode can produce a lithium ion secondary battery with excellent performance.

Further, the electrolytic copper foil of the present invention is particularly suitable as a current collector for a lithium ion secondary battery, and can of course be suitably used as a current collector for electrodes of other batteries.

Example

(Examples 1-1 to 1-7)

An electrolyte containing copper sulfate and sulfuric acid added with an amount of copper, sulfuric acid, chloride ion, tungsten, or thiourea organic additive added in Table 1, with titanium as a noble metal oxide as anode and titanium as a cathode An electrolytic copper foil was produced in accordance with the following electrolysis conditions.

Electrolytic condition

Current density 40A/dm ²

Temperature 45 ° C

In addition, in Table 1 and Table 2, "after heating" means the result of measuring at normal temperature after performing 300 degreeC*1 hour heat processing in an inert gas environment. "Normal temperature" means the result of measurement at room temperature before the above heat treatment. The same is true in the following embodiments.

Anti-rust treatment

The thus-prepared electrolytic copper foil was subjected to rustproof treatment in accordance with the following conditions.

The prepared electrolytic copper foil (untreated copper alloy foil) was immersed in a CrO ₃ ;1 g/L aqueous solution for 5 seconds, subjected to chromate treatment, washed with water, and then dried.

Further, although the chromate treatment has been carried out here, it is of course possible to carry out the treatment with a benzotriazole treatment or a decane coupling agent or a treatment with a decane coupling agent after the chromate treatment.

(Comparative Examples 2-1 and 2-2)

An electrolyte containing copper sulfate and sulfuric acid added with an amount of the copper, sulfuric acid, chlorine, and thiourea organic additives shown in Table 1 is used, the titanium is coated with a noble metal oxide as an anode, and the titanium drum is used as a cathode. The electrolysis conditions were made into electrolytic copper foil.

Electrolytic condition

Current density 40A/dm ²

Temperature 45 ° C

The copper foil thus produced was subjected to the same surface treatment as in the examples.

(Reference Example 2-3)

An electrolyte containing copper sulfate and sulfuric acid added with an amount of copper, sulfuric acid, chloride ion, tungsten, or thiourea organic additive added in Table 1, with titanium as a noble metal oxide as anode and titanium as a cathode An electrolytic copper foil was produced in accordance with the following electrolysis conditions.

Electrolytic condition

Current density 40A/dm ²

Temperature 45 ° C

The copper foil thus produced was subjected to the same surface treatment as in the examples.

The following test was carried out on the produced copper foil.

Determination of tungsten content in copper foil

Regarding the tungsten content, after a certain weight of the electrolytic copper foil was dissolved with an acid, it was calculated by ICP emission spectrometry.

Machine used: ICPS-7000 (Shimadzu Corporation)

Determination of tensile strength of copper foil

The tensile strength of the copper foil is based on IPC-TM-650 before and after heating of the foil.

Machine: AG-I (Shimadzu Corporation)

Determination of chlorine content

After dissolving a certain weight of the electrolytic copper foil with an acid, the chlorine in the solution was quantified by titration with silver nitrate to calculate the chlorine content.

Tungsten analysis

The chemical bonding state and electronic state of tungsten contained in the electrolytic copper alloy were analyzed by XAFS (X-ray Absorption Fine Structure) method. According to the XAFS method, X-rays are irradiated to the sample while changing the X-ray energy, and the chemical bonding state and the electronic state in the sample are analyzed from the obtained X-ray absorption spectrum.

As another method for obtaining an X-ray absorption spectrum, a transmission method for calculating an X-ray absorption spectrum from the intensity of incident X-rays and the intensity of transmitted X-rays, and a measurement of the fluorescence emitted from the sample by absorption of X-rays are exemplified. Fluorescence method of intensity of light X-rays.

When an additive element such as a metal material is used as an analysis target, the amount of addition is a small amount, and it is difficult to obtain an XAFS spectrum by a transmission method. At this time, the above-described fluorescent method is an effective method. The fluorimetry method is characterized in that XAFS measurement can be performed even with elements of a trace component by sufficiently obtaining an irradiation area of X-rays from its optical axis system.

The purpose of this measurement is to know the chemical bonding state and the electronic state of tungsten in the high-strength copper foil. Since the amount of tungsten is a small amount, it is difficult to obtain the XAFS spectrum by the transmission method, and therefore the fluorescence method is selected.

In the measurement, the industry using SPring-8 utilizes the beam line BL14B2. The measured X-ray energy range is 10000~10434eC. This energy range contains the L3-absorption end of tungsten (10207 eV) and is therefore suitable for the purposes of this assay.

The measurement sample was prepared with a copper foil having a tungsten content of 0.48 wt% (Examples 1-3). Further, for comparison, a tungsten foil and WO _{3 were prepared} . As the measurement time, each sample was 4 hours. The spectrum of the tungsten-containing copper foil has a peak in an energy region which does not substantially coincide with the metal tungsten but the spectrum of WO ₃ . Therefore, it is found that the tungsten element in the electrolytic copper foil is contained as an oxide state. Based on the results, it was also measured in each of the examples, and it was confirmed that it was contained in an oxide state.

Battery performance test

Then, the electrolytic copper foil produced in the examples was used as a current collector to prepare a lithium ion secondary battery, and a cycle life test was carried out.

The powdery Si alloy active material (average particle diameter: 0.1 μm to 10 μm) was 85, and the binder (polyimine) was mixed at a ratio of 15 (weight ratio) to be dispersed in N-methylpyrrolidone (solvent). In the formation of an active material slurry.

Then, the slurry was applied to both sides of an electrolytic copper foil having a thickness of 12 μm, dried, and then formed by compression using a roller press, and then sintered at 300 ° C for 1 hour in a nitrogen atmosphere to form a negative electrode. In the negative electrode, the film thickness of the negative electrode mixture after molding was the same on both sides, and both were 20 μm.

Production of lithium ion secondary battery

In the glove box under an argon atmosphere, a three-pole unit for evaluation was constructed by the following structure.

Negative electrode: Si alloy type negative electrode prepared above

Counter electrode, reference pole: lithium foil

Electrolyte: 1 mol/L LiPF ₆ /EC+DEC (3:7 vol%)

The constructed unit was taken out from the tank to the atmosphere, and subjected to charge and discharge measurement in an environment of 25 °C.

Implemented at a constant current relative to the standard unipolar potential standard of Li The battery was charged to 0.02 V, and then the current was lowered to 0.05 C in the CV mode (maintaining a constant potential), and this was ended as charging. In addition, C represents the charge and discharge rate. It was discharged to 1.5 V (Li standard) by a constant current at 0.1 C. The charge and discharge were repeated with the same current of 0.1 C.

The cycle life is the number of cycles when the discharge capacity reaches 70% of the discharge capacity of the first cycle. Further, the battery was disassembled after the charge and discharge cycle, and the deformability of the foil was evaluated. The results are shown in Table 1.

As shown in Table 1, when the tungsten content of the tungsten-containing electrolytic copper foil was 0.06 wt% to 0.5 wt%, no wrinkles and the like were observed after the charge and discharge test, and the cycle characteristics were also good, but in the comparative example exceeding the range, charge and discharge were obtained. Wrinkles occurred after the test and the cycle characteristics were significantly reduced.

Further, the examples in which the tungsten content is in the range of 0.06 wt% to 0.5 wt% have good cycle characteristics as compared with the reference examples outside the range.

Further, although the tungsten content of Examples 1-6 was the same as that of Examples 1-3, the chlorine content exceeded 0.07 wt%, and thus the initial strength was lower than that of Examples 1-3 and Comparative Examples 2-1 and 2-2. However, the strength after heating was higher than that of Comparative Examples 2-1 and 2-2, and it was found that the degree of reduction by heating was small.

However, if the chlorine content exceeds 0.07 wt% as described above, the initial strength may be lowered, the strength value may be lowered after the final heating, and the cycle characteristics may be lowered, so the chlorine content is preferably 0.07 wt% or less.

Making a substrate for HDD suspension

In the present embodiment, after the electrolytic copper foil was produced, a substrate for HDD suspension composed of a stainless foil-polyimine resin layer-electrolytic copper foil was prepared, and its characteristics were evaluated.

Preparation of electrolytic copper foil

As shown in Table 2, the substrates for HDD suspension were produced using the electrolytic copper foils of Examples 1-2 to 4, 1-6, Comparative Example 2-2, and Reference Example 2-3.

Synthesis of polyimine resin

Synthesis Example 1

In order to synthesize a low thermal expansion polyimine resin having a linear expansion coefficient of 30 ppm/K or less, 9.0 mol of DADMB was weighed and dissolved in a 40 L planetary mixer while dissolving in a solvent DMAc 25.5 kg. in. Then, 8.9 mol of BPDA was added, and stirring was continued for 3 hours at room temperature, and polymerization was carried out to obtain a solution of the viscous polyimine precursor A. The polyamidene precursor A obtained in this synthesis example has a linear expansion coefficient of 13 ppm/K after imidization.

Synthesis Example 2

In order to synthesize a polyimine-based resin having a glass transition temperature of 300 ° C or less, 6.3 mol of DADMB was weighed and dissolved in a solvent DMAc of 25.5 kg while stirring in a 40 L planetary mixer. Then, 6.4 mol of BPDA was added, and stirring was continued for 3 hours at room temperature to carry out a polymerization reaction. A solution of the viscous polyimine precursor B is obtained. The glass transition temperature of the polybendimimine precursor B obtained in this synthesis example after imidization was measured using a dynamic viscoelasticity measuring apparatus to be 225 °C.

In addition, the abbreviations used here are as follows.

DADMB: 4,4'-diamino-2,2'-dimethylbiphenyl

DMAc: N,N-dimethylacetamide

BPDA: 3,3',4,4'-biphenyltetracarboxylic dianhydride

BAPP: 2,2'-bis[4-(4-aminophenoxy)phenyl]propane

Fabrication of HDD suspension substrate

Using the electrolytic copper foil prepared in Examples 1-2 to 4, 1-6, Comparative Example 2-2, and Reference Example 2-3, it was made of a stainless foil-polyimine resin layer-electrolytic copper foil. HDD suspension substrate.

(a) The solution of the polyimine precursor B obtained in the synthesis example 2 was applied to a stainless foil (manufactured by Nippon Steel Co., Ltd., SUS304, tension-annealed product, thickness: 20 μm) to be cured. The thickness was 1 μm, and dried at 110 ° C for 3 minutes. (b) Then, a solution of the polyimide precursor A obtained in Synthesis Example 1 was applied thereon to have a thickness of 7.5 μm after hardening. c) drying at 110 ° C for 10 minutes, (d) further coating a solution of the polyimide precursor B obtained in Synthesis Example 2 to a thickness of 1.5 μm after hardening, (e) at 110 Drying at °C for 3 minutes, (f) and then, in the range of 130-360 ° C, the imidization is completed by heat treatment in several stages and each stage for 3 minutes, (g) obtaining poly-pyrene on the stainless foil. The laminate of the amine resin layer having a thickness of 10 μm. Further, the first layer of the polyimide resin layer is the same as the third layer of the polyimide layer.

Then, the prepared electrolytic copper foil was superposed thereon, and subjected to thermocompression bonding under the conditions of a surface pressure of 15 MPa, a temperature of 320 ° C, and a pressing time of 20 minutes using a vacuum press to obtain a target HDD suspension substrate.

Determination of peel strength

For the bonding force between the metal foil and the polyimide resin, after forming a polyimide resin layer on the stainless foil, the electrolytic copper foil is thermocompression-bonded to form a laminate of double-sided metal foil. A test piece for measurement having a wiring width of 1/8 inch was produced by processing into a predetermined shape. The SUS foil side and the copper alloy foil or the copper foil side of the sample were attached to a fixing plate, and each metal foil was peeled off in a 90° direction using a tensile tester, and the peel strength was measured.

Determination of lifting

The laminate was processed to prepare a disc having a diameter of 65 mm, and after standing at a temperature of 23 ° C and a humidity of 50% for 24 hours, the portion which was most tilted when placed on the table was measured using a vernier caliper.

Determination of linear thermal expansion coefficient

When measuring the linear thermal expansion coefficient, the temperature was raised to 255 ° C at a rate of 20 ° C / min using a thermomechanical analyzer (Seiko Instruments Co., Ltd.), and the temperature was maintained at 10 ° C for 10 minutes. Cool at a fixed speed of /min. The average thermal expansion coefficient (linear thermal expansion coefficient) from 240 ° C to 100 ° C at the time of cooling was calculated.

The results are shown in Table 2. The substrate for HDD suspension composed of the stainless foil-polyimine resin layer-electrolytic copper foil made of the electrolytic copper foil of the examples and the reference examples sufficiently satisfies the required characteristics as a suspension substrate material.

Substrate for HDD suspension made of electrolytic copper foil of Comparative Example When it is used as a suspension substrate material, the lift is large and the required characteristics are not satisfied.

As described above, according to the present invention, it is possible to provide an electrolytic copper foil which has a large mechanical strength and is hardly deteriorated after heating at 300 ° C or higher.

Further, according to the present invention, it is possible to provide an excellent electrolytic copper foil as a current collector for a lithium ion secondary battery, and it is possible to provide an excellent secondary battery by using the current collector.

[Industrial Availability]

The electrolytic copper foil of the present invention is suitable for use in a printed wiring board material which is also required to have high mechanical strength after heating, such as a constituent material in the field of HDD suspension materials or TAB materials.

Further, not only a printed wiring board but also a constituent material in a field requiring high mechanical strength and electrical conductivity after high-temperature heating can be applied.

Claims (10)

An electrolytic copper foil containing 0.06 wt% or more of tungsten (W). An electrolytic copper foil containing 0.06 wt% to 0.5 wt% of tungsten (W). An electrolytic copper foil containing tungsten and the remainder consisting essentially of copper. An electrolytic copper foil having a tungsten (W) content of 0.06 wt% to 0.5 wt% and a chlorine (Cl) content of 0.001 wt% to 0.07 wt%. The electrolytic copper foil according to any one of claims 1 to 4, wherein all or part of the tungsten is an oxide. An electrolytic copper foil having a tungsten content of 0.06 wt% to 0.5 wt%, and a tensile strength measured at room temperature after heat treatment at 300 ° C for 1 hour is 500 MPa or more. The electrolytic copper foil has a tungsten content of 0.06 wt% to 0.5 wt%, a chlorine (Cl) content of 0.001 wt% to 0.07 wt%, and a tensile strength of 500 MPa or more measured at room temperature after heat treatment at 300 ° C for 1 hour. A current collector for a secondary battery using the electrolytic copper foil according to any one of claims 1 to 7. An electrode for a secondary battery using the electrolytic copper foil according to any one of claims 1 to 7 as a current collector, and an active material is stacked on the surface of the current collector. A secondary battery using the electrolytic copper foil according to any one of claims 1 to 7 as a current collector.