CN106340668B

CN106340668B - Electrolytic copper foil, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Info

Publication number: CN106340668B
Application number: CN201610412852.0A
Authority: CN
Inventors: 藤泽季实子; 筱崎健作; 筱崎淳; 胡木政登
Original assignee: Furukawa Electric Co Ltd
Current assignee: Furukawa Electric Co Ltd
Priority date: 2015-07-06
Filing date: 2016-06-13
Publication date: 2020-10-23
Anticipated expiration: 2036-06-13
Also published as: TW201702434A; KR101782737B1; CN106340668A; KR20170005764A; TWI609995B; JP2017014608A

Abstract

The invention provides an electrolytic copper foil which is excellent in workability in manufacturing a secondary battery and does not decrease in tensile strength even when heated at 150 ℃ for 1 hour, a negative electrode for a lithium ion secondary battery having an improved cycle life by using the electrolytic copper foil as a current collector, and a lithium ion secondary battery comprising the electrode. An electrolytic copper foil having a matte surface gloss Gs (60 DEG) of 20 to 150, a coefficient of dynamic friction of 0.11 to 0.39, and a tensile strength after heating at 150 ℃ for 1 hour of 350MPa or more, and a lithium ion secondary battery using the electrolytic copper foil as a current collector.

Description

Electrolytic copper foil, negative electrode for lithium ion secondary battery, and lithium ion secondary battery

Technical Field

The present invention relates to an electrolytic copper foil, and a negative electrode for a lithium (Li) ion secondary battery and a lithium ion secondary battery using the electrolytic copper foil.

The present invention also relates to a printed wiring board using the electrolytic copper foil of the present invention, and an electromagnetic shielding material.

Background

A lithium ion secondary battery is mainly used for a mobile phone, a notebook personal computer, and the like, and comprises, for example, a positive electrode having a negative electrode active material layer formed on the surface of a negative electrode current collector (hereinafter simply referred to as a current collector), a negative electrode, and a nonaqueous electrolyte.

The negative electrode of a lithium ion secondary battery is formed by applying carbon particles or the like as a negative electrode active material layer to the surface of a copper foil (negative electrode current collector) and drying the applied copper foil, and further pressing the applied copper foil, which is subjected to a rust-proof treatment with a so-called "untreated copper foil" that has not been subjected to a surface treatment or the like after the production by electrolysis.

In order to obtain sufficient battery characteristics in a lithium ion secondary battery, it is important to reduce the distance between active material particles and the distance between the active material and the current collector, and to deform the shape of the current collector in accordance with the shape of the surface of the active material. When the current collector is deformed in accordance with the shape of the surface of the active material, the contact between the active material and the current collector becomes better, and the electrical conductivity becomes higher, so that desired battery characteristics can be obtained. When the current collector is not deformed in accordance with the shape of the active material surface, the contact portion between the active material and the current collector decreases, and the electrical conductivity decreases, so that desired battery characteristics cannot be obtained.

In addition, when the irregularities on the surface of the current collector are large, the contact point between the active material and the current collector decreases, and the contact resistance increases. When such an electrode having a large contact resistance is repeatedly charged and discharged, the distance between the current collector and the active material gradually increases due to stress caused by expansion and contraction of the active material accompanying charge and discharge, dissolution of a binder into an electrolyte solution, and the like, and the conductivity of a part of the active material becomes conductivity that cannot be used for charge and discharge, thereby causing a decrease in battery capacity. Therefore, it is preferable to use a copper foil having a tensile strength of a predetermined value or more and smoother both surfaces for the negative electrode current collector (patent documents 1, 2, and 3).

However, in recent years, from the viewpoint of productivity, it has been required to increase the transport speed in the battery production process, and if an electrolytic copper foil having a smoother both surfaces is used as a negative electrode current collector of a lithium ion secondary battery, the smooth copper foil tends to slip on the transport roll in an active material coating line, and there is a possibility that wrinkles may occur in the copper foil (current collector) due to the slip, or problems may occur in the active material coating step, or the like.

In addition, in order to reduce the size and weight of the lithium ion secondary battery, it is required to thin the electrolytic copper foil as a current collector. When thinning the copper foil, it is necessary to be able to withstand stress due to expansion and contraction of the active material during charge and discharge, and if the current collector cannot withstand expansion and contraction of the active material, the battery cycle characteristics are adversely affected. Therefore, high strength of the copper foil is an important issue. In addition, when forming an active material layer constituting a negative electrode of conventional carbon-based on a current collector, a paste composed of carbon as a negative electrode active material, a polyvinylidene fluoride resin as a binder, and N-methylpyrrolidone as a solvent is prepared, applied to both surfaces of a copper foil (current collector), and dried. In this case, in order to dry at a temperature of about 150 ℃, the strength of the foil that can withstand expansion and contraction of the active material during charge and discharge is preferably evaluated as the strength after heat treatment at 150 ℃.

As a countermeasure, it is necessary to set the tensile strength of the current collector after the heat treatment to a predetermined value or more.

In addition, recently, printed wiring boards such as rigid printed wiring boards and flexible printed wiring boards are required to have higher adhesion strength between copper foil and film and excellent high-frequency characteristics required for circuit boards.

In addition, a copper foil having a small thickness and strength is also required, and particularly, a copper foil in which foil breakage, wrinkles, and the like are difficult to occur in a manufacturing process of a flexible printed circuit board is required.

In addition, a copper foil capable of maintaining high strength even after undergoing a thermal history in the production of a printed wiring board is also required.

Documents of the prior art

Patent document

Patent document 1: japanese patent No. 3742144;

patent document 2: japanese patent No. 5255229;

patent document 3: japanese patent laid-open No. 2014-224321.

Disclosure of Invention

Technical problem to be solved

An object of the present invention is to provide an electrolytic copper foil which is excellent in tensile strength, does not decrease in tensile strength even when heated at 150 ℃ for 1 hour, and has controlled glossiness and dynamic friction coefficient, and a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the electrolytic copper foil as a current collector.

Another object of the present invention is to provide a copper foil which has high adhesion strength and high frequency characteristics between the copper foil and a film, which are required for a printed circuit board such as a rigid printed circuit board or a flexible printed circuit board, has a small thickness and high strength, and in addition, is less likely to cause foil breakage, wrinkles, and the like particularly in a process for producing a flexible printed circuit board.

Another object of the present invention is to provide a copper foil that can maintain high strength even when subjected to a thermal history during the production of a printed wiring board.

(II) technical scheme

The electrolytic copper foil is characterized in that the gloss Gs (60 DEG) of the matte surface (M surface) is 20 to 150 inclusive, the coefficient of dynamic friction is 0.11 to 0.39 inclusive, and the tensile strength after heating at 150 ℃ for 1 hour is 350MPa to 900MPa inclusive.

The glossiness Gs (60 °) indicates the glossiness measured at an emission-reception light angle of 60 °.

The electrolytic copper foil of the present invention preferably has a tensile strength of 400MPa or more after heat treatment at 150 ℃ for 1 hour.

The negative electrode for a lithium ion secondary battery of the present invention has the electrolytic copper foil of the present invention as a negative electrode current collector.

The lithium ion secondary battery of the present invention is a secondary battery including a negative electrode having the electrolytic copper foil of the present invention as a negative electrode current collector.

The printed wiring board of the present invention uses the electrolytic copper foil as a conductor.

Further, the electromagnetic shielding material of the present invention uses the electrolytic copper foil as a shielding material.

(III) advantageous effects

According to the present invention, there can be provided an electrolytic copper foil characterized in that the matte surface has a gloss Gs (60 °) of 20 to 150 inclusive, a coefficient of dynamic friction of 0.11 to 0.39 inclusive, and a tensile strength after heating at 150 ℃ for 1 hour of 350 to 900MPa inclusive.

The glossiness generally depends on the surface shape in the wavelength range of the visible light region or less, and the coefficient of dynamic friction generally depends on the surface shape (unevenness), the chemical state of the surface (including adsorption of additive components on the outermost surface of the copper foil), and the like.

It is difficult to quantitatively express the range in which the effects of the present invention can be optimally exerted, such as the surface shape and the chemical state of the surface in the scale of the wavelength or less, but the range in which the effects of the present invention can be exerted can be accurately expressed by specifying the glossiness and the coefficient of dynamic friction.

Further, according to the present invention, by using the electrolytic copper foil as a negative electrode current collector, it is possible to provide a secondary battery having good contact between an active material and the current collector, high electrical conductivity, and a good cycle life.

Furthermore, by setting the glossiness Gs (60 °) of the matte surface of the electrolytic copper foil constituting the current collector to 20 to 150, it is possible to exert an anchor effect when fine irregularities on the surface of the current collector adhere to the active material particles, and to suppress the active material from falling off from the current collector when the active material undergoes expansion and contraction during charge and discharge cycles, thereby providing a secondary battery having a good cycle life.

Further, by setting the tensile strength of the electrolytic copper foil constituting the current collector after heating at 150 ℃ for 1 hour to 350MPa or more, it is possible to provide a secondary battery which can withstand stress caused by expansion and contraction of the volume of the active material during charge and discharge and has a good cycle life.

Further, by bonding the electrolytic copper foil to the insulating film, it is possible to provide a printed wiring board (rigid printed wiring board, flexible printed wiring board, etc.) having a higher adhesive strength between the copper foil and the insulating film due to the fine irregularities present on the surface of the copper foil, and having excellent high-frequency characteristics required for a circuit board, for example, capable of preventing an increase in resistance loss and a delay in signal propagation due to a skin effect when a high-frequency signal is applied.

In addition, the electrolytic copper foil of the present invention has a small thickness and strength, and particularly, is less likely to cause foil breakage, wrinkles, and the like in the manufacturing process of a flexible printed circuit board, and can be preferably used for a flexible printed circuit board. Further, by setting the tensile strength of the copper foil after heating at 150 ℃ for 1 hour to 350MPa or more, it is possible to maintain high strength even when the copper foil undergoes a thermal history in the production of a printed wiring board.

The electrolytic copper foil of the present invention has a low contact resistance, excellent high-frequency characteristics, and excellent effects as an electromagnetic shielding material.

In any of the above applications, the gloss Gs (60 °) of the matte surface of the electrolytic copper foil is 20 to 150 and less, and the coefficient of dynamic friction is 0.11 to 0.39, whereby minute irregularities on the surface and organic additives adsorbed on the outermost surface of the copper foil during the production of the copper foil become an antislip material on a transport roll in an active material coating line or the like during the production of a battery, and slippage of the foil on the transport roll is suppressed, and therefore, the workability is good.

Detailed Description

(Structure of electrolytic copper foil)

One embodiment of the present invention will be described with respect to an electrolytic copper foil constituting a current collector for a lithium ion secondary battery. However, the electrolytic copper foil of the present invention can be suitably used not only for a current collector for a lithium ion secondary battery but also for other applications such as a printed circuit board and a conductor for electromagnetic shielding, without changing the gist thereof.

The electrolytic copper foil for a lithium ion secondary battery negative electrode current collector of the present embodiment has a tensile strength of 350MPa or more, particularly preferably 400MPa or more, after heat treatment at 150 ℃ for 1 hour, and can provide a secondary battery that can withstand stress caused by volume expansion and contraction of an active material during charge and discharge and has a good cycle life.

The electrolytic copper foil for a lithium ion secondary battery negative electrode current collector of the present embodiment is provided with a rust-proof treatment layer on at least the surface of the electrolytic copper foil on the side where the active material layer is provided.

Examples of the rust-preventive treatment layer include a chromate treatment layer, a Ni or Ni alloy plating layer, a Co or Co alloy plating layer, a Zn or Zn alloy plating layer, and a Sn or Sn alloy plating layer, and further an inorganic rust-preventive treatment layer such as a chromate treatment layer or an organic rust-preventive treatment layer such as benzotriazole is provided on the above-mentioned various plating layers.

Further, a silane coupling agent treatment layer or the like may be formed.

The inorganic anti-rust treatment, the organic anti-rust treatment, and the silane coupling agent treatment have the effects of improving the adhesion strength between the negative electrode current collector and the active material, and preventing the charge-discharge cycle efficiency of the battery from being reduced.

The electrolytic copper foil for a lithium ion secondary battery current collector of the present embodiment is obtained by, for example, roughening the surface of an electrolytic copper foil provided with an active material layer of the electrolytic copper foil, providing a rust-proof treatment layer on the roughened surface, and further providing a silane coupling agent treatment layer as needed.

The electrolytic copper foil of the present embodiment has a matte surface gloss Gs (60 ℃) of 20 to 150 inclusive and a coefficient of dynamic friction of 0.11 to 0.39 inclusive.

Further, Gs (60 °) represents the glossiness measured at an emission-reception light angle of 60 °.

The reason why the glossiness Gs (60 °) of the matte surface of the electrolytic copper foil is set to 20 or more and 150 or less is that, since the irregularities on the surface of the electrolytic copper foil (current collector) of 20 or less become large, the contact point between the active material and the current collector becomes small, and the electrode has a large contact resistance, when charging and discharging are repeated, the distance between the current collector and the active material gradually becomes large due to stress caused by expansion and contraction of the active material accompanying charging and discharging, dissolution of a binder as an adhesive into an electrolyte solution, and the like, and the electrical conductivity of a part of the active material may become an electrical conductivity that cannot be used for charging and discharging, and the capacity of the secondary battery may be reduced, which is not preferable.

On the other hand, the reason why the glossiness Gs (60 ℃) is 150 or less is to impart adhesiveness and anchor effect to the electrolytic copper foil.

The matte surface of the electrolytic copper foil of the present embodiment has a glossiness Gs (60 °) of 20 to 150 inclusive and a coefficient of kinetic friction of 0.11 to 0.39 inclusive. By providing such an arrangement, the contact between the active material and the current collector is improved, the electrical conductivity is improved, and a good cycle life can be obtained.

The slip of the copper foil on the transport roller and the generation of wrinkles in the battery manufacturing process depend on the surface shape and chemical state of the copper foil. However, the measured value of the surface roughness represented by the ten-point average surface roughness Rz cannot be evaluated sufficiently. This is because a stylus type coarseness gauge having a tip diameter of 2 μm is generally used for the Rz measurement, and the unevenness smaller than that of the stylus cannot be measured in principle. In order to solve this problem, there is also a method of measuring a surface shape including smaller irregularities by an optical measurement method typified by a confocal point laser microscope. However, this method can evaluate the surface shape, but does not include the influence of the surface chemical state, and thus cannot sufficiently evaluate the slip and wrinkle of the copper foil on the transport roll.

In contrast, the inventors of the present invention have found that the evaluation of the glossiness Gs (60 °) and the coefficient of dynamic friction of a more microscopic surface shape can sufficiently evaluate the slip and wrinkle of the copper foil on the conveying roller. Specifically, the glossiness Gs (60 °) of the matte surface of the copper foil is 20 to 150 inclusive, and the coefficient of kinetic friction is 0.11 to 0.39 inclusive, so that fine irregularities on the surface of the copper foil and organic additives adsorbed on the outermost surface of the copper foil become skids on the conveying rollers in the active material coating line in the battery production process, and the slip of the copper foil on the conveying rollers is suppressed, and the copper foil is not wrinkled in the battery production line, thereby improving the workability. The fine irregularities exert an anchoring effect between the active material and the current collector, and are also effective in improving the adhesion of the active material.

That is, when the glossiness Gs (60 °) of the matte surface (M surface) is 20 or more and 150 or less, and the coefficient of dynamic friction is 0.11 or more and 0.39 or less, and more preferably 0.15 or more and 0.35 or less, the handling property is good, and when the glossiness Gs (60 °) is 20 or more and 150 or less, and the tensile strength (before and after heating) is 350MPa or more, the battery characteristics are good.

In addition, with respect to the plain surface (S-surface), conventionally, it has been possible to control the glossiness and the coefficient of dynamic friction relatively easily by controlling the surface shape of the electrolytic drum, but in the present invention, an electrolytic copper foil having both surfaces with predetermined glossiness and coefficient of dynamic friction is realized by focusing on the glossiness and the coefficient of dynamic friction of the matte surface, which have been difficult to control conventionally.

(method for producing electrolytic copper foil)

The electrolytic copper foil for a negative electrode current collector of a lithium ion secondary battery according to the present embodiment can be produced, for example, by supplying an aqueous solution of sulfuric acid-copper sulfate as an electrolytic solution between an insoluble anode made of titanium coated with a platinum group metal element or an oxide thereof and a titanium cathode drum arranged to face the anode, depositing copper on the surface of the cathode drum by passing a direct current between the two electrodes while rotating the cathode drum at a fixed speed, and peeling the deposited copper from the surface of the cathode drum and continuously winding the copper.

As for the tensile strength, a maximum of 900MPa is sufficient.

The electrolytic copper foil for a negative electrode current collector of a lithium ion secondary battery according to the present embodiment can be produced by, for example, electrolytic treatment using an electrolytic plating solution of sulfuric acid-copper sulfate.

The copper concentration of the sulfuric acid-copper sulfate electrolytic plating solution is, for example, preferably 40 to 120g/L, and more preferably 60 to 100 g/L.

The sulfuric acid concentration of the sulfuric acid-copper sulfate electrolytic plating solution is preferably 40 to 60 g/L.

Further, the chlorine concentration of the sulfuric acid-copper sulfate electrolytic plating solution is preferably in the range of 50 to 100 ppm.

The present invention is characterized in that the following organic additives A, B and C are used as additives in an electrolytic (plating) solution.

Examples of the organic additive a include additives having a molecular weight of 100000 or more selected from the group consisting of high molecular weight polysaccharides such as polyethylene glycol, polypropylene glycol, starch, and cellulose-based water-soluble polymers (carboxymethyl cellulose, hydroxyethyl cellulose), and water-soluble high molecular compounds not containing S (sulfur) in the molecular structure such as polyethyleneimine, polyallyl, and polyacrylamide.

As the organic additive B, for example, an additive having a molecular weight of 10000 to 50000 may be used, which is selected from a group consisting of a high molecular weight polysaccharide such as polyethylene glycol, polypropylene glycol, starch, and a cellulose-based water-soluble polymer (carboxymethyl cellulose, hydroxyethyl cellulose), and a water-soluble high molecular compound containing no S (sulfur) in its molecular structure such as polyethyleneimine, polyallyl, and polyacrylamide.

As the organic additive C, for example, an additive having a molecular weight of 1000 to 5000, which is selected from the group consisting of a high molecular weight polysaccharide such as polyethylene glycol, polypropylene glycol, starch, and a cellulose-based water-soluble polymer (carboxymethyl cellulose, hydroxyethyl cellulose), and a water-soluble polymer compound not containing S (sulfur) in its molecular structure such as polyethyleneimine, polyallyl, and polyacrylamide, can be used.

An electrolytic copper foil having a tensile strength of 350MPa or more after heating at 150 ℃ for 1 hour, a gloss Gs (60 DEG) of 20 or more and 150 or less, and a coefficient of kinetic friction of 0.11 or more and 0.39 or less, more preferably 0.15 or more and 0.35 or less can be produced by adding organic additives A (molecular weight of 100000 or more), B (molecular weight of 10000 or more and 50000 or less) and C (molecular weight of 1000 or more and 5000 or less) having different molecular weights in combination and forming a foil under specific electrolytic (plating) conditions.

Generally, organic additives having a small molecular weight (low molecules or polymers having a relatively small molecular weight (e.g., additives C)) are easily introduced into the foil during foil production, and the strength of the foil is increased. At this time, the surface is also generally smoothed.

Further, the introduced impurity components suppress the reduction of strength due to softening of the foil during heating by the pinning effect at the grain boundaries.

On the other hand, since the organic additive has a lower adsorption amount (coating rate) to the outermost surface of the copper foil during foil formation than an organic additive having a large molecular weight (for example, additive A, B), the coefficient of dynamic friction tends to be lowered by the amount even if the surface shape is close to that of the copper foil.

Patent document 2 discloses an electrodeposited copper foil having a normal tensile strength of 700MPa or more and a gloss Gs (60 °) of 80 or more. However, it is known that the foil of patent document 2 has a dynamic friction coefficient of less than 0.11 because of a large influence of the low molecular weight additive, and that the foil slips in the active material application step, thereby causing a problem in handling properties. Patent document 3 discloses an electrodeposited copper foil having a normal tensile strength of 700MPa or more and a gloss Gs (60 °) of 100 or more. However, as in the case of patent document 2, the coefficient of dynamic friction is less than 0.11, and the foil slips in the active material application step, which causes a problem in terms of workability.

In the present invention, additives A and B having larger molecular weights are used in addition to additive C having a relatively low molecular weight.

In particular, since the additive a has a very large molecular weight, it is likely to be adsorbed on the surface of a copper film to inhibit copper deposition during foil formation of a copper foil, thereby having an effect of roughening the surface shape. Further, the amount of adsorption to the outermost surface of the copper foil during foil formation is also large. The adsorbed additive remains on the surface of the copper foil even after the copper foil is subjected to water washing and rust prevention treatment. This also has the effect of increasing the coefficient of dynamic friction.

However, when only the additive a having a molecular weight of 100000 or more is added, the surface becomes too rough, and the coefficient of dynamic friction also exceeds 0.39. Therefore, by adding the additive B having a molecular weight of 10000 or more and 50000 or less, which is relatively smaller than that of the additive a, having an effect of suppressing the effect of the additive a, the coefficient of kinetic friction can be made 0.11 or more and 0.39 or less while the surface thereof is made slightly smooth, and the workability in coating the active material can be improved.

The additives A, B and C can be used in the range of 10-30 mg/L, 5-20 mg/L, and 5-20 mg/L, respectively.

The electrolytic copper foil (untreated copper foil) thus produced is subjected to an inorganic rust-preventive treatment such as chromate treatment, Ni or Ni alloy plating, Co or Co alloy plating, Zn or Zn alloy plating, Sn or Sn alloy plating, chromate treatment on the above-mentioned various plating layers, or an organic rust-preventive treatment such as benzotriazole.

Further, for example, the electrolytic copper foil for a negative electrode collector of a lithium ion secondary battery is produced by treating with a silane coupling agent.

The inorganic anti-rust treatment, the organic anti-rust treatment and the silane coupling agent treatment realize the effects of improving the adhesive strength of the negative electrode current collector and the active material and preventing the charge-discharge cycle efficiency of the battery from being reduced.

Before the rust-proofing treatment, for example, the surface of the electrolytic copper foil may be roughened. As the roughening treatment, for example, a plating method, an etching method, or the like can be suitably used.

The electroplating method is a method of forming a thin film layer having irregularities on the surface of an untreated electrolytic copper foil to thereby roughen the surface. As the plating method, an electrolytic plating method and an electroless plating method can be employed. As roughening by the plating method, it is preferable to form a plating film mainly composed of copper, a copper alloy, or the like on the surface of the untreated electrolytic copper foil.

As the roughening by the etching method, for example, a physical etching method or a chemical etching method is suitably used. As for physical etching, there is a method of etching using sandblasting or the like, and as for chemical etching, various liquids containing an inorganic or organic acid, an oxidizing agent, and an additive have been proposed as a treatment liquid.

(Structure and production method of lithium ion Secondary Battery Using collector for lithium ion Secondary Battery)

The lithium ion secondary battery negative electrode of the present embodiment has a structure in which the electrolytic copper foil for a lithium ion secondary battery negative electrode current collector of the present embodiment described above is used as a negative electrode current collector, and an active material layer is formed on the surface of the current collector subjected to the surface treatment such as the rust-preventive treatment layer.

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

The active material layer in the present embodiment is a material that absorbs and releases lithium, and is preferably an active material that absorbs lithium by alloying it. Examples of such an active material include group 14 elements such as carbon, silicon, germanium, and tin.

In the present embodiment, the current collector is preferably as thin as 4 to 10 μm, and the active material layer is formed on one or both surfaces of the current collector. When the active material is applied only to the smooth surface of the copper foil formed in a drum, the surface of the current collector is smooth, and the adhesion to the active material is good.

If the thickness of the current collector is less than 4 μm, foil breakage tends to occur and the production becomes difficult, and if it is thicker than 10 μm, it is not preferable from the viewpoint of weight reduction and high energy density of the battery. Further, if the coefficient of dynamic friction is 0.11 or less, the surface of the current collector is smooth, and therefore, the surface of the conveyor roll in the copper foil production process or the battery production process is likely to slip and wrinkle. Therefore, for example, by setting the thickness of the copper foil to 4 to 10 μm and the range of the coefficient of kinetic friction to 0.11 to 0.39, the current collector (copper foil) is excellent in workability, and is effective for weight reduction and high energy density of the battery.

In the case of forming a carbon-based negative electrode active material layer, a paste composed of carbon as a negative electrode active material, a polyvinylidene fluoride resin as a binder, and N-methylpyrrolidone as a solvent is prepared, and the paste is applied to one surface or both surfaces of a current collector (copper foil) and dried.

For example, lithium may be previously absorbed or added to the active material layer of the present embodiment. Lithium may be added when forming the active material layer. That is, by forming an active material layer containing lithium, the active material layer contains lithium. In addition, lithium may be absorbed or added to the active material layer after the active material layer is formed. As a method of absorbing or adding lithium to the active material layer, a method of electrochemically absorbing or adding lithium may be cited.

The lithium ion secondary battery of the present embodiment is a lithium ion secondary battery including a positive electrode and a negative electrode, and the negative electrode is constituted by the negative electrode of the lithium ion secondary battery of the present embodiment described above.

(Structure of printed Circuit Board)

The electrolytic copper foil according to the embodiment of the present invention can be used in various fields such as printed circuit boards such as rigid printed circuit boards and flexible printed circuit boards (in this specification, rigid printed circuit boards, flexible printed circuit boards, and the like are sometimes collectively referred to as printed circuit boards), electromagnetic shielding materials, and the like.

Recent printed circuit boards are generally classified into two types. One type is a three-layer printed wiring board in which a copper foil is attached to an insulating film (polyimide, polyester, or the like) with an adhesive resin and patterned by etching. In contrast, another type is a two-layer printed wiring board in which an insulating film (polyimide, liquid crystal polymer, or the like) is directly laminated with a copper foil without using an adhesive.

The electrolytic copper foil according to the embodiment of the present invention is bonded to an insulating film as a conductor of these printed wiring boards.

The main use of printed circuit boards is for flat panel displays such as liquid crystal displays and plasma displays, or for internal wiring of cameras, AV equipment, personal computers, computer terminal equipment, HDDs, cellular phones, automotive electronic equipment, and the like. Since these wirings are mounted in a device in a bent state or used in a place where they are repeatedly bent, excellent bending property is an important characteristic as a required characteristic of a copper foil for a printed circuit board.

The printed wiring board of the present invention can be obtained by attaching the electrolytic copper foil of the embodiment, that is, the electrolytic copper foil having a glossiness Gs (60 °) of 20 or more to the insulating film, so that the printed wiring board has a higher adhesion strength between the copper foil and the insulating film due to the fine irregularities present on the surface of the copper foil and has excellent high-frequency characteristics required for a circuit board.

Further, the copper foil bonded to the insulating film preferably has a tensile strength of 450MPa or more at room temperature, and therefore has strength even when it is a thin foil, and particularly, foil breakage, wrinkles, and the like are less likely to occur in the production process of a flexible printed wiring board.

Further, the tensile strength of the copper foil bonded to the insulating film after heating at 150 ℃ for 1 hour is 350MPa or more, whereby high strength can be maintained even when the copper foil undergoes a thermal history in the production of a printed wiring board.

The electrolytic copper foil of the present invention has excellent electromagnetic shielding effects in many excellent characteristics, for example, high frequency characteristics and low resistance, and is an excellent electromagnetic shielding material by being bonded to an insulating substrate.

In either application, the glossiness Gs (60 °) of the copper foil is 20 or more and 150 or less and the coefficient of dynamic friction is 0.11 or more and 0.39 or less, so that minute irregularities on the surface of the copper foil become skids on the conveying roller, and the slip of the foil on the conveying roller is suppressed, whereby the handling property is good.

Examples

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples, and can be implemented by appropriately changing the examples without changing the gist thereof.

(production of untreated copper foil)

Examples 1 to 8

The copper concentration was adjusted to 65g/L, the sulfuric acid concentration was adjusted to 45g/L, the chloride ion concentration was adjusted to 25ppm, an electrolyte solution to which additives A, B and C shown in Table 1 were added was used, a titanium electrode coated with a noble metal oxide was used as the anode, a titanium rotary drum was used as the cathode, and a current density was 30A/dm²An untreated copper foil having a thickness of 10 μm was produced by an electrolytic foil forming method at a bath temperature of 50 ℃.

Comparative examples 1 to 8

The untreated copper foils of comparative examples 1 to 8 were produced using the same equipment as in examples using the electrolytic solution having the composition shown in Table 2 and the electrolytic conditions so as to have a thickness of 10 μm. Further, comparative example 5 was manufactured according to the method of japanese patent laid-open No. 2014-224321, comparative example 6 was manufactured according to the method of japanese patent No. 3742144, and comparative example 8 was manufactured according to the method of japanese patent No. 5255229.

(measurement of tensile Strength and elongation of electrolytic copper foil)

The results of measuring the tensile strength (MPa) and the elongation (%) of each of the electrodeposited copper foils of examples 1 to 8 and comparative examples 1 to 8 at room temperature are shown in table 3.

Further, tensile strength (MPa) and elongation (%) after heat treatment at 150 ℃ for 1 hour were measured, and the results are shown in table 3.

Tensile strength (MPa) and elongation (%) were measured at room temperature based on IPC-TM-650 using a tensile tester (model 1122 from Instron). The stretching direction is a direction parallel to the longitudinal direction. The longitudinal direction means a direction parallel to the rotation direction of the drum during the electrolytic treatment.

In the present embodiment, "normal temperature" means a normal temperature before the heat treatment at 150 ℃ for 1 hour as described above, and is, for example, a temperature state of about 20 ℃.

(measurement of coefficient of dynamic Friction of electrolytic copper foil)

The coefficient of dynamic friction of the matte surface of each of the electrodeposited copper foils of examples 1 to 8 and comparative examples 1 to 8 was measured using a surface property measuring machine (HEIDON 14FW, manufactured by new eastern science). The measurement was carried out under the following measurement conditions, i.e., 1 single pass at a sliding speed of 100mm/min and a sliding distance of 10mm, while applying a load of 50gf to the slider using a steel ball having a diameter of 10 mm. The results are shown in Table 3.

(measurement of gloss of electrolytic copper foil)

The glossiness Gs (60 °) of the matte surface of each of the electrolytic copper foils of examples 1 to 8 and comparative examples 1 to 8 was measured at a 60 ° transmitting/receiving light angle based on JIS Z8741 using a gloss meter (VG 2000, manufactured by japan electro-color industries, ltd.). The two directions parallel and orthogonal to the long dimension direction were each performed 3 times, and the values obtained by averaging all of these values are shown. The results are shown in Table 3.

[ Table 3]

(chromate treatment)

The surface of each of the electrodeposited copper foils of examples 1 to 8 and comparative examples 1 to 8 was subjected to chromate treatment to form a rust-preventive treatment layer as a current collector.

The chromate treatment of the copper foil surface was performed under the following conditions.

Chromate treatment conditions:

1-10 g/L potassium dichromate

The dipping time is 2-20 seconds

(evaluation of Battery characteristics)

1. Manufacture of positive electrode

Mixing 90 wt% LiCoO₂The powder, 7 wt% graphite powder, and 3 wt% polyvinylidene fluoride powder were mixed, and a solution in which N-methylpyrrolidone was dissolved in ethanol was added and kneaded to prepare a positive electrode paste. This paste was uniformly applied to an aluminum foil having a thickness of 15 μm, and then dried in a nitrogen atmosphere to volatilize ethanol, followed by roll rolling to produce a sheet having an overall thickness of 100 μm. After the sheet was cut to a width of 43mm and a length of 290mm, a lead terminal of aluminum foil was attached as a positive electrode at one end thereof by ultrasonic welding.

2. Manufacture of negative electrode

A paste was prepared by mixing 90 wt% natural graphite powder (average particle size 10 μm) and 10 wt% polyvinylidene fluoride powder, adding a solution of N-methylpyrrolidone dissolved in ethanol, and kneading. Next, the paste was applied to both surfaces of each copper foil of examples and comparative examples. The coated copper foil was dried in a nitrogen atmosphere to volatilize ethanol, and then roll-rolled to form a sheet having an overall thickness of 110 μm. The sheet was cut into a width of 43mm and a length of 285mm, and then a lead terminal of nickel foil was attached as a negative electrode by ultrasonic welding at one end thereof.

3. Manufacturing the battery:

a separator made of polypropylene having a thickness of 25 μm was sandwiched between the positive electrode and the negative electrode manufactured as described above, and the whole was rolled up, and contained in a battery can having a soft steel surface plated with nickel, and the lead terminal of the negative electrode was spot-welded to the bottom of the case. Next, an upper cover of an insulating material was placed, a gasket was inserted, and then ultrasonic welding was performed to connect the lead terminal of the positive electrode and a safety valve made of aluminum, a nonaqueous electrolytic solution composed of propylene carbonate, diethyl carbonate, and ethylene carbonate was injected into the battery case, and then a cover was attached to the safety valve to assemble a sealed structure type lithium ion secondary battery having an external shape of 14mm and a height of 50 mm.

4. Measurement of Battery characteristics

The above batteries were subjected to a charge-discharge cycle test in which one cycle of the test was such that charging was performed at a charging current of 50mA until 4.2V was reached and discharging was performed at 50mA until 2.5V was reached. The battery capacity and cycle life at the time of initial charging are shown in table 3. Further, the cycle life is the number of cycles when the discharge capacity of the battery drops to 300 mAh.

5. Evaluation of good working Property

In the coating treatment of 1000m foil on the active material coating line, the foil was marked as good in handling property, i.e., the foil was smoothly conveyed without slipping on the conveying roller and without being stuck on the conveying roller; the foil that caused a phenomenon of slippage or jamming of the foil on the roller and causing a conveyance stop was marked x as a case of poor operability, and the results are shown in table 3. In addition, foils which, although somewhat problematic with regard to transport, do not cause problems with the application of the active substance are marked Δ.

From table 3, in examples 1 to 8, the tensile strength before and after heating at 150 ℃ for 1 hour was 350MPa or more, and the glossiness Gs (60 °) was 20 or more, and therefore, the battery characteristics were good with a cycle life of 500 cycles or more. Further, the coefficient of dynamic friction is 0.11 to 0.39, and slip on the roll during production line production can be suppressed, and the workability is also good.

However, in example 1, the dynamic friction coefficient was as high as 0.38, and the application of the active material was not hindered, but the operability was marked as Δ because some cards were observed in the transportation.

On the other hand, the foil of example 8 had a dynamic friction coefficient as low as 0.12, and therefore, it was confirmed that the foil somewhat slipped on the feed roll, but the application of the active material was not hindered, and therefore, the mark was Δ in the same manner as in example 1.

The copper foil of comparative example 1 had a very low glossiness Gs (60 °) of 20 or less on the matte side, and therefore had poor contact between the active material and the current collector, and could not withstand the stress caused by expansion and contraction of the active material during charge and discharge, and had a cycle life of 500 cycles or less, since the active material layer formed on the matte side had peeled off, and the like. Further, the coefficient of dynamic friction on the matte side is 0.38, which is relatively high, and therefore the foil may get stuck on the transport roller, but this does not cause a problem in applying the active material.

The copper foil of comparative example 2 had a tensile strength after heating of 350MPa or more and a glossiness Gs (60 °) on the matte side of 20 or more and 150 or less, and thus exhibited a preferable cycle life, but the dynamic friction coefficient on the matte side was as low as 0.11 or less, and therefore the foil slipped during conveyance in the active material application step, and therefore the handling property was poor.

The copper foil of comparative example 3 had a tensile strength after heating of 350MPa or more and a glossiness Gs (60 °) of 20 or more, and therefore the contact between the active material formed on the matte side and the current collector was good, and the result was that the cycle life was 500 cycles or more. However, in terms of workability, since the coefficient of dynamic friction on the rough surface side is very high, the foil is caught and stopped on the transport roller, and there is a problem in coating the active material, and therefore, the workability is not preferable.

The copper foil of comparative example 4 had a coefficient of dynamic friction on the matte side of 0.13 and good workability in application of the active material, but since the glossiness Gs (60 °) was 150 or more, peeling of the active material occurred due to expansion and contraction of the active material during charge and discharge, and the cycle life was less than 500 cycles, which was not preferable.

Comparative example 5 is a foil produced by the method for producing example (sample 8) described in patent document 3.

The tensile strength after heating is 350MPa or more, and the glossiness Gs (60 °) on the matte side is also 20 to 150, and therefore, the preferable cycle life is shown, but the workability is not preferable because the dynamic friction coefficient on the matte side is as low as 0.11 or less, and the slip of the foil occurs during transportation in the active material application step.

In addition, comparative example 6 is a foil produced by the method described in the example of patent document 1. The coefficient of dynamic friction on the rough surface side is in the range of 0.11 to 0.39, respectively, so that the handling property in the active material application step is preferable, and the glossiness Gs (60 °) is also in the range of 20 to 150, and therefore the adhesion property between the active material and the current collector is also preferable, but the tensile strength after heating is 320MPa and as low as less than 350MPa, so that the expansion and contraction of the active material during charge and discharge cannot be tolerated, and the foil deformation and the like occur, and the cycle characteristics are deficient due to this influence, and the mark is x.

Similarly, in comparative example 7, though the handling property was good at the time of coating the active material, the foil was deformed at the time of charge and discharge due to the tensile strength after heating being as low as less than 350MPa, and the cycle characteristics were poor.

Comparative example 8 is a foil produced by the method described in the example of patent document 2, and shows a preferable cycle life because the tensile strength after heating is 350MPa or more and the glossiness Gs (60 °) on the matte side is also 20 or more and 150 or less, but the dynamic friction coefficient on the matte side is 0.11 or less, and the foil slips during transportation in the active material application step, and therefore the handling property is poor.

As described above, the electrolytic copper foil of the present invention uses an electrolytic copper foil having a tensile strength after heating at 150 ℃ for 1 hour of 350MPa or more, preferably 400MPa or more, a matte gloss Gs (60 °) of 20 or more and 150 or less, and a coefficient of dynamic friction of 0.11 or more and 0.39 or less, preferably 0.15 or more and 0.35 or less, and thus can provide an electrolytic copper foil that shows good lithium ion secondary battery characteristics, is less likely to slip on a production line, and has good workability when producing on the production line.

The electrolytic copper foil according to the example of the present invention has a tensile strength of 350MPa or more after heating at 150 ℃ for 1 hour, and can withstand stress caused by expansion and contraction of the volume of the active material during charge and discharge, and a secondary battery having a good cycle life can be obtained.

Further, the electrolytic copper foil of the example of the present invention has a glossiness Gs (60 °) of 20 to 150 in the matte surface, and thus has good contact between the active material and the current collector, high electrical conductivity, and a good cycle life.

Further, the electrolytic copper foil of the present invention has a gloss Gs (60 °) of 150 or less and a coefficient of dynamic friction of 0.11 to 0.39, and the fine irregularities on the surface become a slip-preventing material on the transfer roll, so that the slip of the foil on the roll can be suppressed, and the workability can be improved.

In addition, the lithium ion secondary battery negative electrode of the present invention uses the electrolytic copper foil of the present invention as a current collector, thereby being a lithium ion secondary battery negative electrode having improved cycle characteristics, and a lithium ion secondary battery including the electrode is a battery having an excellent cycle life.

(production and evaluation of printed Circuit Board)

The electrolytic copper foil of example 5 was laminated with a polyimide film to produce a 3-layer printed wiring board, and the production process and the performance of the completed wiring board were evaluated.

(1) Adhesion of copper foil to film

With respect to adhesion between the copper foil and the film, the polyimide film is embedded in minute irregularities present on the surface of the copper foil and has satisfactory strength.

(2) High frequency characteristics

Regarding the high frequency characteristics of the printed wiring board, the glossiness Gs (60 °) is 90 or more, and the unevenness of the copper foil surface is minute, and thus it is satisfactory.

(3) Strength of copper foil and generation of wrinkles

The tensile strength of the copper foil at room temperature is 668MPa, and is 450MPa or more, so that the strength of bonding with the insulating film is sufficient even with a thin foil, and foil breakage, wrinkles, and the like do not occur in the manufacturing process of the printed wiring board.

(4) Thermal history

In the heating process when the copper foil is bonded with the insulating film, the strength change of the copper foil caused by the thermal history is hardly found, and the high strength can be maintained even if the thermal history in the manufacture of the printed circuit board is passed.

As described above, the present invention is particularly excellent as a copper foil for a secondary battery collector having a long cycle life and has excellent workability, and therefore the copper foil does not wrinkle on an active material coating line, and according to such characteristics, the present invention has an excellent effect that a lithium ion secondary battery negative electrode having improved cycle characteristics can be easily provided, and a lithium ion secondary battery having a long cycle life including the lithium ion secondary battery negative electrode can be provided.

In addition, as described above, the present invention has an excellent effect that a printed circuit board and an electromagnetic shielding material having excellent characteristics can be provided.

Claims

1. An electrolytic copper foil characterized in that the matte surface has a gloss Gs (60 DEG) of 20 to 150 inclusive, a coefficient of dynamic friction of 0.11 to 0.39 inclusive, a small decrease in tensile strength after heating, and a tensile strength after heating at 150 ℃ for 1 hour of 350 to 900MPa inclusive.

2. The electrolytic copper foil according to claim 1, wherein the tensile strength after heating at 150 ℃ for 1 hour is 400MPa or more.

3. The electrolytic copper foil according to claim 1 or 2, wherein the electrolytic copper foil has a thickness of 4 μm or more and 10 μm or less.

4. A negative electrode for a lithium ion secondary battery, characterized in that the electrolytic copper foil according to any one of claims 1 to 3 is used as a current collector.

5. A lithium ion secondary battery using the negative electrode for a lithium ion secondary battery as a current collector according to claim 4.

6. A printed wiring board comprising the electrolytic copper foil according to any one of claims 1 to 3 and an insulating film laminated thereon.

7. An electromagnetic shielding material comprising the electrolytic copper foil according to any one of claims 1 to 3 and an insulating substrate laminated together.