JP5916904B1 - Electrolytic copper foil, negative electrode for lithium ion secondary battery, lithium ion secondary battery, rigid printed wiring board and flexible printed wiring board - Google Patents

Abstract

An object of the present invention is to provide an excellent handling property in which the tensile strength is not significantly reduced by a high-temperature heat treatment applied in the manufacturing process of a rigid printed wiring board, a flexible printed wiring board or a lithium ion secondary battery, When a lithium ion secondary battery is configured as a current collector for a negative electrode, an electrolytic copper foil capable of obtaining a good cycle life is provided. The electrolytic copper foil of the present invention contains 150 ppm or more of carbon, 200 ppm or more of chlorine and 50 ppm or less of sulfur as impurities in the foil, and after heating at 450 ° C. for 1 hour at a normal tensile strength of 450 MPa or more. The tensile strength measured at room temperature is 350 MPa or more. [Selection] Figure 1

Description

  The present invention relates to an electrolytic copper foil, a negative electrode for a lithium (Li) ion secondary battery and a lithium ion secondary battery using the same. The present invention further relates to a rigid printed wiring board and a flexible printed wiring board using the electrolytic copper foil as a conductive material.

  Copper foil is used as a current collector for a battery such as a lithium ion secondary battery. A lithium ion secondary battery is basically composed of a positive electrode, a negative electrode, and an electrolytic solution. The negative electrode is formed by coating the surface of a copper foil used as a current collector with a negative electrode active material layer. As a method for forming the negative electrode, a slurry obtained by dissolving a negative electrode active material and a binder resin (added for the purpose of binding the active material and the copper foil substrate) in a solvent is applied onto the copper foil substrate, and then the binder resin is formed. A method of forming by pressing after drying at a temperature equal to or higher than the curing temperature is generally used. As the binder resin, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR) and the like are widely used.

  In recent years, active materials made of silicon, tin, germanium alloy materials, etc. with high theoretical capacity, which have been attracting attention as the capacity of batteries increases, have a very large volume expansion coefficient due to lithium insertion / extraction during charging / discharging. The above-mentioned binder resin is large and lacks strength. Therefore, a polyimide resin having a high adhesive strength with a copper substrate has attracted attention. However, unlike the binder resin described above, the polyimide resin has a very high curing temperature of about 300 ° C. Furthermore, in order to shorten the drying time, heat treatment at a high temperature of 450 ° C. or higher is required. Therefore, a negative electrode current collector (copper foil) that can withstand heat treatment at 450 ° C. is required.

  Copper foil is used in various fields such as rigid printed wiring boards, flexible printed wiring boards, electromagnetic wave shielding materials, battery current collectors, and the like. Among these fields, in the field of printed wiring boards (flexible wiring boards, hereinafter referred to as “FPC”) bonded to polyimide films, hard disk (hereinafter referred to as “HDD”) suspension materials or tape automation. The bonding (hereinafter referred to as “TAB”) material has been required to improve the strength of the copper foil.

  The suspension mounted on the HDD is a wiring-integrated type that has stable flying head buoyancy and positional accuracy relative to the disk that is the storage medium, compared to the conventionally used wire-type suspension as the HDD capacity increases. Most of the suspension has been replaced.

This wiring-integrated suspension has the following three types.
a. A type in which a flexible printed circuit board called FSA (flex suspension assembly) method is processed and bonded using an adhesive b. Type that forms wiring by forming amic acid, which is a precursor of polyimide resin called CIS (Circuit Integrated Suspension), and then imidizing and plating on polyimide. C.TSA (Trace Suspension / Assembly) type that processes a laminated body made of stainless steel foil-polyimide resin-copper foil into a predetermined shape by etching

The TSA suspension can easily form flying leads by laminating copper foils with high strength, and has a high degree of freedom in shape processing and is relatively inexpensive and has good dimensional accuracy. Widely used.
The laminate formed by the TSA method is manufactured using a material having a stainless steel foil thickness of about 12 to 30 μm, a polyimide layer thickness of about 5 to 20 μm, and a copper foil thickness of about 7 to 14 μm. In the production of the laminate, first, a polyimide resin solution is applied onto a stainless steel foil as a base. After the application, the solvent is removed by preheating, and then further heat treatment is performed to perform imidization. Subsequently, a copper foil is overlaid on the imidized polyimide resin layer and laminated by thermocompression bonding to produce a laminate composed of stainless steel layer / polyimide layer / copper layer.

  The heating temperature during the imidization is generally about 300 ° C., but a treatment at a high temperature of about 450 ° C. is required to shorten the manufacturing time. In this heat treatment at about 450 ° C., the stainless steel layer (foil) constituting the laminate is hardly changed in size, but a copper layer (foil) formed using a conventional electrolytic copper foil is 450 Annealing was performed at a temperature of about 0 ° C., recrystallization proceeded, and softened, resulting in a dimensional change. Along with this, there was a tendency that the laminate was warped after lamination, and the dimensional accuracy of the product was lowered. Therefore, it is required to develop a copper foil with as small a dimensional change during heating as possible.

In the TAB material, as with the HDD suspension material, it is required to increase the strength of the copper foil and reduce the roughness of the foil surface. In a TAB product, a plurality of terminals of an IC chip are directly bonded to inner leads (flying leads) arranged in a device hole located substantially at the center of the product. This bonding is performed by applying a constant bonding pressure by instantaneously energizing and heating using a bonding apparatus. At this time, there is a problem that the inner lead obtained by etching the electrolytic copper foil is stretched by being pulled by the bonding pressure.
Furthermore, if the strength of the electrolytic copper foil is low, the inner lead may sag due to plastic deformation and may break if it is significant. Therefore, in order to reduce the line width of the inner lead, the electrolytic copper foil to be used is required to have a roughened surface with low roughness and to have high strength.

  Also in this case, it is necessary that the copper foil has high strength in a normal state (normal temperature / normal pressure state) and has high strength even after being heated. In the case of a TAB application, a two-layer or three-layer FPC in which a copper foil and a polyimide are bonded together is used. In the case of bonding the polyimide to the copper foil in the three-layer FPC, an epoxy adhesive is used and the bonding is performed at a temperature of about 180 ° C. In addition, in a two-layer FPC using a polyimide adhesive, bonding is performed at a temperature of about 450 ° C.

  Even if the electrolytic copper foil has a high mechanical strength in a normal state, it does not make sense if the electrolytic copper foil softens when bonded to polyimide. Conventional high-strength electrolytic copper foil has high mechanical strength in the normal state, and even if heated at around 180 ° C, the mechanical strength hardly changes, but when heated at about 450 ° C, it is annealed and recrystallization proceeds. Therefore, it softens rapidly and the mechanical strength decreases. Such a copper foil is not suitable for TAB applications.

  As described above, in the FPC field and the secondary battery field, a polyimide resin having a very high curing temperature of about 300 ° C. has been used, and more than 450 ° C. for shortening the processing time. Therefore, a copper foil that can withstand this heat treatment is required.

  Patent Document 1 discloses an electrolytic copper foil having a normal tensile strength (normal tensile strength) of 500 to 750 MPa and a tensile strength (tensile strength) after heating at 400 ° C. for 1 hour of 350 MPa or more. However, the electrolytic copper foil disclosed in Patent Document 1 is not clear in terms of the concentration of impurities in the foil, and the tensile strength after heat treatment at 450 ° C. or higher (measured at room temperature) Nothing is shown.

Patent Document 2 discloses that a tensile strength value in a normal state (normal tensile strength) is 70 kgf / mm ² (686 MPa) to 100 kgf / mm ² (980 MPa), and a tensile strength after heating at 180 ° C. for 60 minutes. The electrolytic copper foil whose thickness value is 85% or more of the value of the normal tensile strength is disclosed. However, the electrolytic copper foil disclosed in Patent Document 2 is not certain in the concentration of impurities in the foil, and the tensile strength after heat treatment at a high temperature of 450 ° C. or higher (measured at room temperature) Nothing is shown.

In Patent Document 3, the sulfur concentration in the copper foil is 10 mass ppm or more and 50 mass ppm or less, the normal tensile strength (normal tensile strength) is 50 kgf / mm ² (490 MPa) or more, and after heating at 250 ° C. for 30 minutes. Discloses an electrolytic copper foil having a tensile strength (tensile strength) of 90% or more of the normal tensile strength. However, the electrolytic copper foil disclosed in Patent Document 3 does not focus on the concentration of impurities other than sulfur in the copper foil, and after heat treatment at a high temperature of 450 ° C. or higher (measured at room temperature) There is also no indication of the tensile strength.

JP 2013-181236 A JP 2008-101267 A Japanese Patent No. 5148726

Shoji Shiga, “Physical properties of polyacrylamide-added electrodeposited copper -Possibility of molecular dispersion strengthened alloys-”, Metal surface technology, 1980, Vol.31, No10, p.573-574

  The purpose of the present invention is that the tensile strength is not significantly reduced by high-temperature heat treatment applied in the production process of a rigid printed wiring board, a flexible printed wiring board or a lithium ion secondary battery, and has excellent handling properties. An object of the present invention is to provide an electrolytic copper foil capable of obtaining a good cycle life when a lithium ion secondary battery is configured as a current collector for a negative electrode.

In order to achieve the above object, the gist of the present invention is as follows.
(I) The foil contains 150 ppm or more of carbon as impurities, 200 ppm or more of chlorine, and 50 ppm or less of sulfur, the normal tensile strength is 450 MPa or more, and the tensile strength measured at room temperature after heating at 450 ° C. for 1 hour is 350 MPa. The electrolytic copper foil characterized by the above.

(II) A negative electrode for a lithium ion secondary battery, wherein the electrolytic copper foil according to (I) is used as a current collector.

(III) A lithium ion secondary battery using the negative electrode for a lithium ion secondary battery according to (II) above.

(IV) A rigid printed wiring board using the electrolytic copper foil according to (I) as a conductive material.

(V) A flexible printed wiring board using the electrolytic copper foil according to (I) above as a conductive material.

  The copper foil of the present invention contained carbon as an impurity in the foil at 150 ppm or more, chlorine at 200 ppm or more, and sulfur at 50 ppm or less, and the normal tensile strength was 450 MPa or more, measured at room temperature after heating at 450 ° C. for 1 hour. Since the tensile strength is 350 MPa or more, lithium ions having a good cycle life can withstand stress due to volume expansion and contraction of the active material during charge and discharge after battery formation even after a heat treatment step at a high temperature of 450 ° C. A secondary battery can be provided. Further, when the sulfur content is 50 ppm or less as an impurity component in the foil, the foil does not become brittle, and the foil is hardly broken in the transporting process in the battery production line, and the handling property is improved. Furthermore, by using such a copper foil, it has sufficient tensile strength even after a heat treatment process at a high temperature of 450 ° C., and has good handling properties, for a rigid printed wiring board or a flexible printed wiring board. An electrolytic copper foil can be provided.

FIG. 1 relates to the electrolytic copper foils used in the present invention (Example 4) and Comparative Example 4, respectively, at normal temperature after heating in a normal state (normal temperature: 20 ° C.) and within a temperature range of 150 to 500 ° C. It is the figure which plotted the data of the measured tensile strength.

[Configuration of electrolytic copper foil]
Hereinafter, this embodiment demonstrates the electrolytic copper foil which comprises the collector for lithium ion secondary batteries. However, the electrolytic copper foil of the present invention is not used only for a current collector for a lithium ion secondary battery, and can be used for other purposes as appropriate without changing the gist thereof.

The electrolytic copper foil for the negative electrode current collector of the lithium ion secondary battery of the present embodiment contains 150 ppm or more of carbon, 200 ppm or more of chlorine and 50 ppm or less of sulfur as impurities in the foil, and a normal tensile strength of 450 MPa or more, 450 By making the tensile strength measured at room temperature after heating at ℃ for 1 hour to be 350 MPa or more, the handling property at the time of battery production is good, and it can withstand the stress due to the volume expansion and contraction of the active material during charge and discharge, A secondary battery having a good cycle life can be provided.
In the present embodiment, the “normal state” means a state where the copper foil is placed at room temperature without receiving a thermal history such as heat treatment after the manufacture of the copper foil. Moreover, normal temperature refers to 20 degreeC.

  By the way, an electrolytic solution containing copper sulfate and sulfuric acid is used as an electrolytic solution used for the production of electrolytic copper foil, and plating is performed for the purpose of making the copper foil surface bright and smooth, reducing the stress of the copper foil, etc. Various additives are added to the bath. When the additive is not used, the surface form and mechanical properties required for the copper foil cannot be obtained, so the additive is very important. In particular, since the copper sulfate plating bath is a simple acidic bath, it is inferior in throwing power and it is difficult to produce a preferable electrolytic copper foil without an additive. As additives used in copper sulfate plating baths, chlorine ions, polyoxyethylene surfactants, smoothing agents, brighteners such as organic sulfides, glue, gelatin, etc. have been proposed and used. .

  Many organic additives that are added to the electrolytic solution at the time of copper foil production usually have an effect of suppressing crystal growth, and it is considered that a part of the organic additive is taken into the crystal grain boundary with the precipitation of copper. In this case, the mechanical strength tends to improve as the amount of the organic additive taken into the crystal grain boundary increases (see, for example, Non-Patent Document 1).

  Such electrolytic copper foil suppresses the softening phenomenon during heat treatment due to the pinning effect caused by inclusions derived from organic additives incorporated into the grain boundaries, but when heated at a high temperature of 450 ° C. or higher The inclusions are decomposed and gasified to escape, so that the tensile strength is drastically reduced. Further, the trace of the impurity component being lost tends to be a void and the foil tends to be brittle.

  When the present inventors present at the grain boundary as a cluster of carbon (C) and chlorine (Cl) formed when carbon is incorporated as an impurity in the foil at 150 ppm or more and chlorine is incorporated at 200 ppm or more, 450 ° C. It has been found that even when the above heat treatment is performed, the impurity components are not decomposed and the tensile strength is not rapidly reduced. However, if sulfur is contained in the foil in an amount of more than 50 ppm as an impurity component, the crystal grain boundary becomes brittle and the foil is easily broken, which is not preferable.

  For this reason, in the present invention, carbon contained 150 ppm or more, chlorine 200 ppm or more, and sulfur 50 ppm or less as impurities in the foil, and the normal tensile strength was 450 MPa or more, measured at room temperature after heating at 450 ° C. for 1 hour. An essential invention specific matter was that the tensile strength was 350 MPa or more.

  Moreover, for example, it is preferable that the electrolytic copper foil for a lithium ion secondary battery current collector of the present embodiment is provided with a rust prevention treatment layer on at least the surface on the side where the active material layer is provided on the electrolytic copper foil. The antirust treatment layer is, for example, a chromate treatment layer, or a nickel or Ni alloy plating layer, a Co or Co alloy plating layer, a Zn or Zn alloy plating layer, a Sn or Sn alloy plating layer, or a chromate treatment on the above various plating layers. It is an inorganic rust-proofing layer such as one provided with a layer, or an organic rust-proofing layer such as benzotriazole. Furthermore, a silane coupling agent treatment layer or the like may be formed.

  The inorganic rust-proofing layer, the organic rust-proofing layer, and the silane coupling agent-treated layer increase the adhesion strength with the active material and prevent the charge / discharge cycle efficiency of the battery from decreasing. In addition, for example, the electrolytic copper foil for a lithium ion secondary battery current collector of the present embodiment is subjected to a roughening treatment on the surface on which the active material layer of the electrolytic copper foil is provided, and the surface subjected to the roughening treatment is applied to the surface. A rust-proofing layer is provided, and a silane coupling agent-treated layer is provided if necessary.

[Method for producing electrolytic copper foil]
The electrolytic copper foil for the negative electrode current collector of the lithium ion secondary battery according to the present embodiment includes, for example, an insoluble anode made of titanium coated with a platinum group element or an oxide element thereof, using a sulfuric acid-copper sulfate aqueous solution as an electrolytic solution, The above-mentioned electrolyte is supplied between a titanium cathode drum provided opposite to the anode, and a DC current is passed between both electrodes while rotating the cathode drum at a constant speed. The copper is deposited, and the deposited copper is peeled off from the surface of the cathode drum and continuously wound.

  The electrolytic copper foil for a lithium ion secondary battery negative electrode current collector of the present embodiment can be produced, for example, by performing an electrolytic treatment using a sulfuric acid-copper sulfate electrolytic plating solution. As a copper concentration of a sulfuric acid-copper sulfate electroplating solution, it is preferable to set it as the range of 40-120 g / L, for example, More preferably, it is the range of 60-100 g / L. The sulfuric acid concentration of the sulfuric acid-copper sulfate electroplating solution is preferably in the range of 40 to 60 g / L. Furthermore, the chlorine concentration of the sulfuric acid-copper sulfate electroplating solution is preferably in the range of 50 to 100 ppm.

  Moreover, it is preferable to use the organic additives A, B, and C shown below as additives in the electrolytic (plating) solution.

  The organic additive A is, for example, in a molecular structure such as polyethylene glycol, polypropylene glycol, starch, polymer polysaccharides such as cellulose water-soluble polymer (carboxyl methyl cellulose, hydroxyethyl cellulose, etc.), polyethylene imine, polyallyl, polyacrylamide and the like. Among additives selected from water-soluble polymer compounds not containing S (sulfur), those having a molecular weight of 100,000 or more can be used.

  The organic additive B is, for example, in a molecular structure such as polyethylene glycol, polypropylene glycol, starch, a high molecular polysaccharide such as a cellulose-based water-soluble polymer (carboxyl methyl cellulose, hydroxyethyl cellulose, etc.), polyethylene imine, polyallyl, polyacrylamide, etc. Among additives selected from water-soluble polymer compounds not containing S (sulfur), those having a molecular weight of 10,000 or more and 50,000 or less can be used.

  The organic additive C is, for example, in a molecular structure such as polyethylene glycol, polypropylene glycol, starch, high molecular polysaccharides such as cellulose water-soluble polymer (carboxyl methyl cellulose, hydroxyethyl cellulose, etc.), polyethylene imine, polyallyl, polyacrylamide, etc. Among additives selected from water-soluble polymer compounds not containing S (sulfur), those having a molecular weight of 1000 or more and 5000 or less can be used.

  By adding a combination of organic additives A, B and C having different molecular weights and performing foil formation under specific electrolysis (plating) conditions, incorporation of impurity components into the foil is controlled, and carbon as an impurity is 150 ppm or more, A copper foil containing 200 ppm or more of chlorine and 50 ppm or less of sulfur, having a normal tensile strength of 450 MPa or more and heating at 450 ° C. for 1 hour and having a tensile strength measured at room temperature of 350 MPa or more can be produced.

  For the produced electrolytic copper foil (untreated copper foil), for example, chromate treatment, Ni or Ni alloy plating, Co or Co alloy plating, Zn or Zn alloy plating, Sn or Sn alloy plating, the above various plating layers An inorganic antirust treatment such as a chromate treatment or an organic antirust treatment such as benzotriazole. Furthermore, for example, a silane coupling agent treatment or the like is performed to obtain an electrolytic copper foil for a negative electrode current collector of a lithium ion secondary battery. The inorganic rust prevention treatment, organic rust prevention treatment, and silane coupling agent treatment increase the adhesion strength with the active material and prevent the charge / discharge cycle efficiency of the battery from being lowered.

  Moreover, before performing said rust prevention process, it is also possible to perform a roughening process, for example to the electrolytic copper foil surface. As the roughening treatment, for example, a plating method or an etching method can be suitably employed. The plating method is a method of roughening the surface by forming a thin film layer having irregularities on the surface of the untreated electrolytic copper foil. As the plating method, an electrolytic plating method and an electroless plating method can be employed. As the roughening by the plating method, a method of forming a plating film mainly composed of copper such as copper or copper alloy on the surface of the untreated electrolytic copper foil is preferable. As the roughening by the etching method, for example, a method by physical etching or chemical etching is suitable. Physical etching includes a method of etching by sandblasting or the like, and chemical etching can be performed using a known solution containing an inorganic or organic acid, an oxidizing agent, and an additive as a processing solution.

[Configuration and production method of lithium ion secondary battery using current collector for lithium ion secondary battery]
The lithium ion secondary battery negative electrode of the present embodiment uses the electrolytic copper foil for the lithium ion secondary battery negative electrode collector of the present embodiment as a current collector, and the rust-proofing layer of the current collector is formed. In other words, the active material layer is formed on the surface that has been subjected to the surface treatment. For example, the active material layer is obtained by applying a slurry obtained by kneading an active material, a binder, and a solvent to a negative electrode current collector, drying, and pressing.

  The active material layer in the present embodiment is a material that occludes / releases lithium, and is preferably an active material that occludes lithium by alloying. Examples of such an active material include group 14 elements such as carbon, silicon, germanium, and tin. In the present embodiment, the active material layer can be formed on one side or both sides of the current collector.

  When the sulfur component in the foil is 50 ppm or less, the foil is not brittle, and the foil does not break during transportation in the copper foil manufacturing process and the battery manufacturing process. However, when the sulfur component in the foil is higher than 50 ppm, the foil becomes brittle, and the foil is broken during transportation in the copper foil manufacturing process and the battery manufacturing process. Therefore, by including 150 ppm or more of carbon as impurities, 200 ppm or more of chlorine and 50 ppm or less of sulfur as impurities in the foil, the handling property in the battery manufacturing process is good, and the heat treatment in the high capacity battery manufacturing process using the polyimide binder It becomes an effective current collector (copper foil) that can withstand the process.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof. Is.

[Manufacture of untreated copper foil]
<Examples 1-6>
A copper concentration was adjusted to 65 g / L, a sulfuric acid concentration was adjusted to 45 g / L, and a chloride ion concentration was adjusted to 80 ppm, and an electrolyte solution containing the additives A, B, and C shown in Table 1 was used. A titanium rotating drum was used for the electrode and cathode, and the conditions were a current density of 30 A / dm ² and a bath temperature of 50 ° C., and an untreated copper foil having a thickness of 6 to 12 μm was produced by an electrolytic foil method.

<Comparative Examples 1-6>
Using electrolytes with additives A, B, and C shown in Table 1, a noble metal oxide-coated titanium electrode for the anode and a titanium rotating drum for the cathode, current density 30 A / dm ² , bath temperature 50 ° C. The untreated copper foil having a thickness of 10 μm was produced by the electrolytic foil method. Comparative Example 4 was made based on the technique disclosed in Patent Document 1, Comparative Example 5 was Patent Document 2, and Comparative Example 6 was made in accordance with the technique disclosed in Patent Document 3.

[Measurement of tensile strength and elongation of electrolytic copper foil]
About each electrolytic copper foil of Examples 1-6 and Comparative Examples 1-6, the tensile strength (MPa) and elongation rate (%) in a normal state (normal temperature: 20 degreeC) were measured. The results are shown in Table 2. Further, the tensile strength (MPa) and the elongation rate (%) were also measured after heat treatment heated at 450 ° C. for 1 hour, and the results are also shown in Table 2. In addition, the tensile strength and elongation rate were implemented by the method based on IPC-TM-650 using the tensile testing machine (Instron company make type 1122).

[Measurement of surface roughness Rz]
Ten-point average roughness Rz (μm) was measured for the surfaces of the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 6. The measurement was performed by the method defined in JIS B 0601: 1994, and the results are shown in Table 2.

[Measurement of impurities in foil]
The amount of impurities (concentration) of sulfur and carbon in copper foil was measured by surface cleaning with acetone and drying, followed by combustion in an oxygen stream using a carbon sulfur analyzer (EMIA-920 made by HORIBA) by infrared absorption method. did. Moreover, the amount of impurities (concentration) of nitrogen in the copper foil is measured by surface cleaning with acetone and drying, followed by an inert gas melting-thermal conductivity method using an oxygen-nitrogen analyzer (EMGA-920 manufactured by HORIBA). It was measured. The measurement of the chlorine concentration in the foil is carried out by washing the surface with acetone, drying and dissolving a certain weight of electrolytic copper foil with acid, and titrating the chlorine in the solution with silver nitrate using an automatic titrator (COM1600 manufactured by HIRANUMA). It was measured.

[Chromate treatment]
The surface of each electrolytic copper foil of Examples 1 to 6 and Comparative Examples 1 to 6 was subjected to chromate treatment to form a rust preventive treatment layer to obtain a current collector. The conditions for the chromate treatment of the copper foil surface are as follows.

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

[Evaluation of battery characteristics]
Next, using the electrolytic copper foils of Examples 1 to 6 and Comparative Examples 1 to 6 subjected to the chromate treatment as described above as current collectors, lithium secondary batteries were produced and subjected to a cycle life test. Powdered Si alloy-based active material (average particle size 0.1 μm to 10 μm) and binder (polyimide) are mixed at a ratio (weight ratio) of 85:15 and dispersed in N-methylpyrrolidone (solvent). An active material slurry was obtained. Next, this slurry was applied to both sides of the produced electrolytic copper foil, dried, and compressed and formed with a roller press, and then sintered under a nitrogen atmosphere at 450 ° C. for 1 hour to produce a negative electrode. . In this negative electrode, the negative electrode mixture after molding had the same film thickness of 20 μm on both sides.

<Production of lithium secondary battery>
In a glove box under an argon atmosphere, a three-electrode cell for evaluation was constructed with the following configuration.

Negative electrode: Si alloy-based negative electrode produced above Counter electrode and reference electrode: both lithium foil Electrolyte: 1 mol / l LiPF ₆ / EC + DEC (3: 7 vol%)

[Evaluation of good cycle life]
The constructed cell was taken out from the box into the atmosphere, and charge / discharge measurement was performed in an atmosphere at 25 ° C. Charging was performed at a constant current up to 0.02 V with respect to the standard unipolar potential of Li, and thereafter, the charging was terminated when the CV (with constant potential) current decreased by 0.05 C. Discharge was performed at a constant current up to 1.5 V (Li reference) at 0.1 C. Charging / discharging was repeated with the same current equivalent to 0.1 C. The cycle life is the number of cycles when the discharge capacity of the battery is less than 80% of the initial discharge capacity. The cycle life is “Good” when the number of cycles is 450 cycles or more, especially “Good”, “Good” when 400 cycles or more and less than 450 cycles, and Bad when less than 400 cycles. “×” is attached as there is. The results are shown in Table 2.

[Handling evaluation]
In the coating process of a 2000 m long foil using the active material coating line, “○” indicates that the foil breakage on the transport roll did not occur as “good”, and if the fracture occurred, “ “×” was attached. The results are shown in Table 2.

  From the results in Table 2, the copper foils of Examples 1 to 6 have no sulfur breakage during transport of the foil in the battery manufacturing process because the sulfur content in the foil is 5 to 46 ppm and 50 ppm or less. Handling property is good, and the carbon content in the foil is 175 to 865 ppm and 150 ppm or more, and the chlorine content in the foil is 260 to 684 ppm and 200 ppm or more, so that the normal tensile strength is 474 to In addition to being 721 MPa and 450 MPa or more, the tensile strength measured at room temperature after heating at 450 ° C. for 1 hour is maintained at a high value of 362 to 609 MPa and 350 MPa or more, and the cycle life is also good at 400 cycles or more. The characteristics are shown. In particular, regarding the copper foils of Examples 5 and 6, the cycle life was a more preferable result of 450 cycles or more. Regarding these copper foils, it was found that nitrogen was contained at a concentration of 100 ppm or more in addition to chlorine and carbon. As a result of the study, by containing 150 ppm or more of carbon and 200 ppm or more of carbon, a copper foil that can withstand heat treatment at 450 ° C. is obtained, and by using such a copper foil as a current collector, the battery has 400 cycles or more. Although the cycle life is good, nitrogen is also contained in the foil at a concentration of 100 ppm or more, so that the smoothness of the copper foil surface is increased and the adhesion to the active material layer is increased, and the cycle characteristics are further improved. I found out.

  On the other hand, since the copper content of Comparative Example 1 has a sulfur content in the foil exceeding 59 ppm and 50 ppm, the grain boundary becomes unhealthy, and the foil breaks during the transport experiment, so the handling property is inferior. It was. Further, Comparative Example 2 has a carbon content in the foil of 103 ppm and less than 150 ppm, and Comparative Example 3 has a chlorine content in the foil of 145 ppm and less than 200 ppm. , Because inclusions composed of contributing C-Cl clusters could not be formed, and the tensile strength decreased to 336 MPa and 324 MPa by heat treatment at 450 ° C., respectively, so that the foil could not withstand the stress accompanying active material expansion and contraction during charging and discharging. The cycle life was inferior to less than 400 cycles due to deformation or breakage. Furthermore, Comparative Example 4 is a copper foil made based on the technique disclosed in Patent Document 1, but the chlorine content in the foil is 5 ppm and less than 200 ppm, so it is heated at 450 ° C. for 1 hour. Since the later tensile strength was less than 342 MPa and 350 MPa, the cycle life was also inferior to less than 400 cycles. Further, Comparative Example 5 is a copper foil manufactured by the method disclosed in Patent Document 2, but since the sulfur content in the foil is higher than 75 ppm and 50 ppm, the foil is brittle and breaks during a transportation experiment. In addition, since the handleability is inferior, and the carbon concentration in the foil is less than 121 ppm and 150 ppm, the heat treatment at 450 ° C. for 1 hour makes the foil tensile strength less than 330 MPa and 350 MPa, and the cycle life is also 400 cycles. It was inferior with less. Furthermore, Comparative Example 6 is a copper foil manufactured by the method disclosed in Patent Document 3, but the carbon content in the foil is less than 50 ppm and 150 ppm, and the chlorine content is also less than 15 ppm and 200 ppm. The cycle life was inferior to less than 400 cycles because the foil could not withstand the heat treatment at 450 ° C. for 1 hour and the tensile strength of the foil was less than 345 MPa and 350 MPa.

  Moreover, regarding the electrolytic copper foil used in each of Example 4 and Comparative Example 4, the tensile strength in the normal state (normal temperature: 20 ° C.) and the temperatures of 150, 200, 250, 300, 350, 400, 450, and 500 ° C. FIG. 1 shows a plot of tensile strength data measured at room temperature after heating for 1 hour. From FIG. 1, Example 4 has a normal tensile strength of 608 MPa and a tendency that the tensile strength decreases as the heating temperature increases, but the tensile strength when the heating temperature is 450 ° C. is 504 MPa, and the heating temperature is Since the tensile strength at 500 ° C. is 486 MPa, both of which are considerably higher than 350 MPa, even if the heating temperature is as high as 450 ° C. or higher, the decrease rate of the tensile strength with respect to the normal tensile strength is small. On the other hand, in Comparative Example 4, although the normal tensile strength was 735 MPa, which was higher than the normal tensile strength in Example 4, the tensile strength when the heating temperature was 450 ° C. was as low as 342 MPa and less than 350 MPa. When the temperature becomes 450 ° C. or higher, the tensile strength decreases rapidly, and the rate of decrease in tensile strength with respect to the normal tensile strength is large.

  According to the present invention, a lithium ion secondary battery that can withstand stress due to active material volume expansion and contraction during charge and discharge after battery formation even after a heat treatment step at a high temperature of 450 ° C. and has a good cycle life is provided. Can be provided. Further, when the sulfur content is 50 ppm or less as an impurity component in the foil, the foil does not become brittle, and the foil is hardly broken in the transporting process in the battery production line, and the handling property is improved. Furthermore, by using such a copper foil, it has sufficient tensile strength even after a heat treatment process at a high temperature of 450 ° C., and has good handling properties, for a rigid printed wiring board or a flexible printed wiring board. An electrolytic copper foil can be provided.

Claims (5)

  The foil contains 150 ppm or more of carbon as impurities, 200 ppm or more of chlorine, and 50 ppm or less of sulfur, the normal tensile strength is 450 MPa or more, and the tensile strength measured at room temperature after heating at 450 ° C. for 1 hour is 350 MPa or more. An electrolytic copper foil characterized by that.   A negative electrode for a lithium ion secondary battery, wherein the electrolytic copper foil according to claim 1 is used as a current collector.   A lithium ion secondary battery using the negative electrode for a lithium ion secondary battery according to claim 2.   A rigid printed wiring board comprising the electrolytic copper foil according to claim 1 as a conductive material.   A flexible printed wiring board using the electrolytic copper foil according to claim 1 as a conductive material.

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