JP2013187114A - Copper foil for lithium secondary battery collector, and display method thereof, negative electrode for lithium secondary battery using copper foil, and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil as a negative electrode collector (electrode material) that can hold excellent charge/discharge cycle life characteristics and a high battery capacity in the initial stage of charging, as the electrode material for Li battery, and to provide a manufacturing method thereof, and a rustproof treatment not using chromium so as to dispel the influence of environmental pollution due to hexavalent chromium because of the environmental problem.SOLUTION: An alloy layer of a low melting point metal and copper is provided on at least one surface of an untreated copper foil, and a cobalt layer or an alloy layer of cobalt and a low melting point metal is provided thereon thus obtaining a copper foil for an Li battery collector. Preferably, the low melting point metal is zinc, tin, bismuth or indium.

Description

The present invention relates to a copper foil as a current collector for a lithium secondary battery (Li battery), and more particularly to a copper foil (current collector) constituting a negative electrode by depositing a negative electrode active material.
Furthermore, this invention relates to the electrode for Li batteries using this copper foil, and a Li battery.

Due to demands such as downsizing of electronic devices such as mobile phones and video cameras, and mounting on hybrid vehicles and electric vehicles, the consumption of Li batteries, which have high energy density, excellent charge / discharge characteristics, and light weight, has increased. Development is also actively underway.
As an electrode material for the negative electrode of a Li battery, a copper foil is generally used as a current collector, and a negative electrode active material such as graphite is applied to the surface of the copper foil, dried, and then crimped by roll rolling or the like to obtain a copper foil surface. The active material is deposited on the negative electrode.
The positive electrode current collector is made of aluminum foil or the like, and lithium cobalt oxide is deposited to form a positive electrode. The positive electrode and the negative electrode are wound in a cylindrical shape through a separator and are in contact with the organic electrolyte. A type Li battery is formed.
In addition, there are a square type, a coin type, a Li battery using a polymer electrolyte, and the like.

  The negative electrode of the Li battery uses a carbon powder having an average particle size of about 20 μm as an active material, artificial graphite, natural graphite, coke, etc. as an active material, and the active material is dispersed in a solvent together with a binder to form a slurry. The applied active material is applied to a current collector (copper foil), dried, and further roll-bonded to a thickness of about several tens of μm to form a negative electrode. Usually, organic PVDF (polyvinylidene fluoride) is used as the binder, and NMP (normal methylpyrrolidone) is used as the solvent.

As active materials other than carbon, Sn-based alloys (for example, Sn—O compounds), Si-based alloys (for example, Si—O compounds), metal nitrides, and the like have been researched and developed to demonstrate the performance of these active materials. Various current collectors (copper foil) have been proposed.
For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2005-350761), a cobalt layer is directly formed on a copper foil by plating, and has a high tensile strength even after heat treatment at a high temperature, and the copper foil is used as a current collector. It has been proposed that a non-aqueous electrolyte secondary battery having high charge / discharge characteristics can be obtained.
Further, in Patent Document 2 (Japanese Patent Laid-Open No. 2006-269362), a barrier layer made of nickel or cobalt is provided on the surface of a copper foil, a copper or tin plating film is formed on the barrier layer, and heat treatment is performed to obtain an Li battery. Proposals for use as negative electrodes have been made.
In Patent Document 3 (Japanese Patent Laid-Open No. 2004-22306), an intermediate layer made of cobalt or the like is provided between a copper foil and an active material made of tin, and the copper foil surface and the intermediate layer metal are compatible. An anode for an Li battery as an alloy layer is disclosed.
However, all the current collectors for Li battery negative electrodes disclosed in these documents have a cobalt layer formed directly on the surface of the copper foil.
When the cobalt layer is directly formed on the surface of the copper foil, the surface resistance is increased, and the copper foil is not preferable as a Li battery current collector. For this reason, in order to prevent the resistance increase on the copper foil surface, it is necessary to make the cobalt layer thin. However, when the cobalt layer is thinned, the tensile strength is lowered, and when the copper foil is used as a current collector, the copper foil surface is likely to be eluted, making it unsuitable as a current collector for a Li battery.

Currently, a copper foil having a thickness of about 8 to 20 μm is mainly used as the copper foil for the negative electrode current collector. However, in recent years, the thickness of the copper foil used for increasing the capacity of the battery has been reduced, and the thickness is 12 μm or less. Copper foil has been adopted.
As the copper foil, an electrolytic copper foil electrodeposited on a drum such as titanium from a solution containing copper sulfate as a main component or a rolled copper foil rolled from a thick strip is used.
Since the processing oil is indispensable for the production of the rolled copper foil, the processing oil is inevitably contaminated and has a disadvantage that the adhesion with the active material is inferior. Moreover, although it is said that it is superior to an electrolytic copper foil in terms of mechanical strength, there are problems of inferior productivity due to a narrow manufacturing width and a problem of cost increase by dealing with thin foils.
Therefore, since it is difficult to adopt a copper foil of 12 μm or less by rolling (rolled copper foil) as a negative electrode of a Li battery in terms of technology and cost, a copper foil having a thickness of 12 μm or less is adopted.

Further, the copper foil as the Li battery current collector is often subjected to chromate treatment, organic rust prevention treatment, and the like on the surface thereof.
Since the negative electrode active material is deposited and adhered on the surface of the copper foil subjected to such rust prevention treatment, the adhesion strength between the negative electrode active material and the copper foil surface is greatly influenced by the surface treatment of the copper foil. That is, due to the adhesion of the active material to the copper foil, the charge / discharge cycle life characteristics, which are the most important characteristics for the battery, and the battery capacity at the initial stage of charging are greatly affected. Therefore, provision of the copper foil which has the surface excellent in adhesiveness with a negative electrode active material is requested | required.
However, there are concerns about the impact of environmental pollution caused by hexavalent chromium due to environmental problems, and we are heading towards regulation. As described above, since hexavalent chromium is used in the chromate treatment, it is extremely difficult to deal with environmental problems, and this alternative technique is desired.

JP-A-2005-350761 JP 2006-269362 A JP 2004-022306 A

  Rust prevention treatment is indispensable for copper foil surface to prevent oxidation. As a current collector for the negative electrode of a Li battery, a negative electrode active material is deposited and adhered to the surface of a copper foil that has been subjected to a rust prevention treatment, so the adhesion strength between the negative electrode active material and the copper foil surface is a rust prevention treatment on the copper foil surface. It is greatly influenced by. That is, due to the adhesion of the active material to the copper foil, the charge / discharge cycle life characteristics, which are the most important characteristics for the battery, and the battery capacity at the initial stage of charging are greatly affected. Therefore, provision of the copper foil which has the surface excellent in adhesiveness with a negative electrode active material is requested | required.

The present invention solves the problems of copper foil as an electrode material for Li batteries, and as a negative electrode current collector (electrode material) capable of maintaining excellent charge / discharge cycle life characteristics and high battery capacity at the beginning of charging. It aims at provision of copper foil and its manufacturing method.
On the other hand, there are concerns about the impact of environmental pollution by hexavalent chromium due to environmental problems, and it is heading toward regulation. As described above, since hexavalent chromium is used in the chromate treatment, it is extremely difficult to deal with environmental problems, and an alternative technique is desired.

  As a result of intensive studies in view of the above problems, the copper foil of the present invention is an environment-friendly electrode material because there is no layer containing hexavalent chromium on the surface, and a material with improved characteristics compared to organic rust prevention treatment. By using such a material, it is possible to provide a current collector (copper foil) that is environmentally friendly and that can maintain excellent charge / discharge cycle life characteristics and a high battery capacity at the beginning of charging, and the current collector. An object of the present invention is to provide a Li battery using the above.

The copper foil for the Li battery current collector of the present invention is provided with an alloy layer of a metal having a low melting point and copper on at least one surface of the untreated copper foil, on which a cobalt layer or a metal having a low melting point of cobalt and metal This is a copper foil for a lithium secondary battery current collector provided with the above alloy layer.
The metal having a low melting point is a metal having a melting point of 500 ° C. or lower, and is preferably zinc (Zn), tin (Sn), bismuth (Bi), or indium (In).

  The alloy layer of the metal having a low melting point and copper is a Zn—Cu alloy layer, and the zinc content in the Zn—Cu alloy layer is preferably 1 wt% or less.

  The method for producing a copper foil for a current collector of a lithium secondary battery according to the present invention comprises subjecting at least one surface of an untreated copper foil to an alloy layer of cobalt and a metal having a low melting point by electrolytic plating, And a copper foil for a lithium secondary battery current collector, in which an alloy layer of Cu and a metal having a low melting point is formed on the surface of the copper foil.

  In the method for producing a copper foil for a lithium secondary battery current collector of the present invention, a metal having a low melting point is plated on at least one surface of an untreated copper foil, and a cobalt layer is plated on the metal layer having the low melting point. And then heat-treating the copper layer having the low melting point metal layer and the cobalt layer to form an alloy layer of Cu and a metal having a low melting point on the surface of the copper foil. Is the method.

  The method for producing a copper foil for a current collector of a lithium secondary battery according to the present invention comprises applying a metal layer having a low melting point to at least one surface of an untreated copper foil by plating, and heat treating the copper foil provided with the metal layer having a low melting point Then, an alloy layer of Cu and a metal layer having a low melting point is formed on the surface of the copper foil, and then a cobalt layer is plated thereon to produce a copper foil for a lithium secondary battery current collector.

  The negative electrode current collector for a lithium secondary battery current collector of the present invention is a negative electrode for a lithium secondary battery in which the copper foil of the present invention is used as a current collector and an active material is deposited on the current collector.

  The lithium secondary battery of the present invention is a lithium secondary battery having the negative electrode of the present invention as a negative electrode.

The copper foil of the present invention forms an alloy layer of a low melting point metal and copper on the surface of the untreated copper foil, and forms a cobalt layer thereon, thereby suppressing the amount of cobalt adhesion as much as possible, and a current collector for a Li battery As a result, it is possible to provide a surface-treated copper foil that does not elute copper foil, is hard, does not easily wrinkle, and does not increase electrical resistance so much.
In the present invention, by using the surface-treated copper foil as a current collector, it is easy to handle, has little shape collapse after forming the active material, has good adhesion to the active material, and effectively elutions the copper foil. It has an excellent effect of preventing and providing a Li battery having good cycle characteristics as a battery.

It is a schematic diagram which shows one Embodiment of this invention. It is explanatory drawing which shows the surface treatment process which shows one Embodiment of this invention.

The terms used in this specification are defined as follows.
The “Li battery” is a lithium secondary battery. The shape includes a cylindrical shape and a flat shape.
“Untreated copper foil” refers to an untreated electrolytic copper foil that has been electrolytically formed and an untreated rolled copper foil that has been rolled and does not need to be expressed separately.
The “metal having a low melting point” is a metal having a melting point of 500 ° C. or lower. Hereinafter, the “metal having a low melting point” may be expressed as a “low melting point metal”.

The copper foil for a Li battery electrode of the present invention is a copper foil in which an untreated copper foil surface is provided with an alloy layer of Cu and a low melting point metal, and a cobalt layer or an alloy layer of cobalt and a low melting point metal thereon. . As the low melting point metal, Zn, Sn, Bi, In or the like is preferably used.
As the untreated copper foil, either a rolled copper foil or an electrolytic copper foil may be used. However, when using a rolled copper foil, the remaining of rolling oil causes a decrease in active material adhesion and a cobalt-containing layer. Since unevenness may occur when forming, care must be taken to clean the surface. As a cleaning method, it is preferable to perform alkali dipping, electrolytic degreasing, and pickling treatment with sulfuric acid and the like.

  The copper foil for the Li battery current collector of the present invention is provided with an alloy layer of copper and a low melting point metal (Zn, Sn, Bi, In, etc.) on the surface of the untreated copper foil, and then cobalt or cobalt and a low melting point metal ( An alloy layer with Zn, Sn, Bi, In, etc.) and heat-treated to form a low melting point metal-containing copper alloy layer on the surface of the copper foil, to suppress the cobalt adhesion amount of the outermost layer as much as possible, to prevent elution of the copper foil, The copper foil does not increase the electrical resistance so much.

In addition, the copper foil for the Li battery current collector of the present invention is provided with a low melting point metal such as Zn, Sn, Bi, In or the like on the surface of the untreated copper foil, and the low melting point metal and the copper foil surface contain the low melting point metal. A copper alloy layer is formed, and the cobalt adhesion amount of the cobalt layer provided on the copper alloy layer is suppressed as much as possible to prevent elution of the copper foil, so that the electric resistance does not increase so much.
The copper foil of the present invention covers the surface of the untreated copper foil with an alloy film of a low melting point metal and copper, and provides a cobalt layer on which the cobalt adhesion amount is suppressed as much as possible, compared with a normal copper foil. It becomes a hard foil, and the copper foil does not easily become wrinkles. Accordingly, the copper foil is easy to handle during battery production, and has a characteristic that the shape is less likely to collapse after the active material is formed. In addition, the copper foil is excellent as a current collector for a Li battery negative electrode having a low electrical resistance, good adhesion to the active material, effectively preventing elution of the copper foil, and good cycle characteristics as a battery.

As one embodiment of the present invention, when Zn is adopted as the low melting point metal, the Zn content of the Zn—Cu alloy layer is preferably 1 wt% or less.
The Zn content is 1 wt% or less in order to suppress the decrease in the conductivity of the copper foil as much as possible, and the conductivity compared with Cu is 95% with the thickness of the cobalt layer (including the cobalt alloy layer) coated thereon. This is to suppress the IACS to more than that.

In this embodiment, Zn is adopted as the low melting point metal, and a Zn—Co alloy layer is provided on the surface of the untreated copper foil by electrolytic plating to a thickness of 0.05 to 5 mg / dm ² . Next, the copper foil coated with the Zn—Co alloy layer is heat-treated in an air atmosphere at 50 ° C. to 300 ° C. for 30 seconds to 5 hours. With this heat treatment, Zn in the Co—Zn alloy is thermally diffused into Cu on the surface of the copper foil to be alloyed.

Note that, if necessary, an inclination gradient can be given to the Zn content of the Zn—Co alloy. Since Zn is easily dissolved in acid, if the Zn-Co alloy plating is applied in two stages, the concentration on the surface of the copper foil is high, and the gradient can be lowered as the distance from the surface of the copper foil increases. The gradient rate is preferably 10% or less.
Thus, the Co amount in the Zn-Co alloy layer having a Zn concentration gradient was coated on the surface of the untreated copper foil to a thickness of 0.05 to 5 mg / dm ² , and then the Zn-Co alloy layer was coated. By heat-treating the copper foil in an air atmosphere at 50 ° C. to 300 ° C. for 30 seconds to 5 hours, a copper alloy layer containing 1 wt% or less of Zn by thermal diffusion can be formed at the interface of the untreated copper foil. .
In the above description, the Zn—Co alloy layer is provided on the copper foil surface. However, it is also possible to provide a Zn layer on the copper foil surface and then provide a Co layer for heat treatment.
It is also possible to provide a Zn layer on the copper foil surface and heat-treat, and then provide a Co layer thereon.

Thus, by providing a Zn layer or Zn—Co alloy layer on the surface of the copper foil, a Zn—Cu alloy layer with few impurities can be formed, and oxidative corrosion of the copper foil during atmospheric heating can be prevented. By providing a coating of Zn—Cu alloy on the surface of such a copper foil, a surface layer harder than Cu can be obtained, and the tensile strength of the entire foil can be increased.
In view of manufacturing cycle time, the heat treatment is preferably 150 ° C. × 30 seconds. Further, the Co—Cu alloy is not formed by setting the heat treatment temperature to 300 ° C. or less.
That is, the outermost layer of the copper foil becomes a cobalt or cobalt-zinc alloy surface by heat treatment at 300 ° C. or lower. By making the copper foil surface a cobalt layer or a cobalt alloy layer, the wettability between the surface and the active material slurry using the water-dispersed binder is remarkably improved, and the adhesion with the binder is This is a significant improvement over conventional copper foil. As described above, the Co—Cu alloy layer is not formed on the outermost layer of the copper foil. In the Co—Cu alloy layer, the wetting between the copper foil surface and the slurry of the active material using the water dispersion binder is performed. This is because the sex is improved.

The zinc layer formed on the surface of the untreated copper foil is formed by plating. As a Zn ion supply source of the plating solution, one kind or a mixture of two kinds such as zinc sulfate and zinc chloride can be used.
The total amount of Zn content in the Zn plating solution is 1 to 100 g / L, preferably 3 to 50 g / L, as Zn metal. Zinc sulfate, zinc chloride or the like is dissolved in a solution to which an alkali such as sodium hydroxide is added to form a plating solution. The amount of sodium hydroxide is 20 to 200 g / L, preferably 40 to 150 g / L.

In the plating treatment, the untreated copper foil is subjected to cathode (cathode) electrolysis in the Zn-containing plating solution. Current density, 0.05 to 15 A / dm ² is preferred. If the current density exceeds this, gas generation becomes intense and electrodeposition of inevitable impurities tends to occur, which is not preferable.
The Zn content in the plating solution is 1 to 100 g / L, preferably 3 to 50 g / L, as Zn metal. If the Zn content is exceeded, the Zn content may be 1 wt% or more due to thermal diffusion with the copper foil surface, which is not preferable.

Next, the copper foil provided with the zinc layer is heat-treated at 50 ° C. to 300 ° C. in an air atmosphere for 30 seconds to 5 hours. By performing heat treatment, a Cu—Zn alloy layer is formed of Cu and Zn on the surface of the copper foil.

In the present embodiment, the cobalt layer is formed by plating. As a cobalt ion supply source of the plating solution, one kind or a mixture of two or more kinds such as cobalt sulfate and cobalt chloride can be used.
The total amount of cobalt content in the cobalt plating solution is 5 to 100 g / L, preferably 10 to 50 g / L, as cobalt metal.

In the plating process, the Zn-treated copper foil is subjected to cathode (cathode) electrolysis in a cobalt-containing plating solution. Current density, 0.05 to 15 A / dm ² is preferred. If the current density exceeds this, the generation of gas becomes violent and electrodeposition of inevitable impurities tends to occur, which is not preferable.
The thickness of the cobalt film thus obtained is preferably 0.05 to 5 mg / dm ^2, and if the upper limit thickness is exceeded, the conductivity will be 95% IACS or less. It is not preferable. More preferably 0.1~4mg / dm ^2.
In addition, the measurement of the amount of cobalt in a cobalt containing film | membrane can be measured by the method of melt | dissolving the whole copper foil and calculating | requiring by the atomic absorption method.

The Co—Zn alloy layer formed on the surface of the untreated copper foil is formed by plating. As a cobalt ion supply source of the plating solution, one kind or a mixture of two or more kinds such as cobalt sulfate and cobalt chloride can be used. As a zinc ion supply source of the plating solution, one or a mixture of two kinds such as zinc sulfate and zinc chloride can be used.
The total amount of cobalt content in the Co—Zn alloy plating solution is 5 to 200 g / L, preferably 20 to 60 g / L, as cobalt metal. The total zinc content is 0.01 to 80 g / L, preferably 0.05 to 40 g / L.

The pH of the plating solution of this embodiment is preferably adjusted to 2.0 to 7.0, preferably 3.0 to 6.0 by adding acid or alkali.
In the plating treatment, an untreated copper foil is subjected to cathode (cathode) electrolysis in a plating solution containing cobalt and zinc. Current density, 0.05~10A / dm ² is preferred. If the current density exceeds this, gas generation becomes intense and electrodeposition of inevitable impurities occurs, which is not preferable.
The thickness of the Co—Zn film thus obtained is preferably 0.05 to 5 mg / dm ^2, and if it exceeds this thickness, the electrical conductivity is lowered, which is not preferable. More preferably 0.1~4mg / dm ^2.

The Co—Sn alloy layer formed on the surface of the untreated copper foil is formed by plating. As a cobalt ion supply source of the plating solution, one kind or a mixture of two or more kinds such as cobalt sulfate and cobalt chloride can be used. As a tin ion supply source of the plating solution, one kind or a mixture of two kinds such as tin sulfate and tin chloride can be used.
The total amount of cobalt content in the Co—Sn alloy plating solution is 5 to 200 g / L, preferably 20 to 60 g / L, as cobalt metal. The total tin content is 1-150 g / L, preferably 5-80 g / L.

The pH of the plating solution in this embodiment is preferably adjusted to 4 to 10, preferably 6 to 8, by adding acid or alkali.
In the plating process, an untreated copper foil is subjected to cathode (cathode) electrolysis in a plating solution containing cobalt and tin. Current density, 0.05~10A / dm ² is preferred. If the current density exceeds this, gas generation becomes intense and electrodeposition of inevitable impurities occurs, which is not preferable.
The thickness of the Co—Zn film thus obtained is preferably 0.05 to 5 mg / dm ^2, and if it exceeds this thickness, the electrical conductivity is lowered, which is not preferable. More preferably 0.1~4mg / dm ^2.

Next, the untreated copper foil provided with the Co—Sn alloy is heat-treated in an air atmosphere at 50 ° C. to 300 ° C. for 30 seconds to 5 hours. By performing heat treatment, a Cu—Sn alloy layer is formed of Cu and Sn on the surface of the copper foil.
Next, a cobalt layer is provided on the surface of the Cu—Sn alloy layer. The formation of the cobalt layer is the same as the conditions formed by plating on the surface of the zinc layer.

The Co—Bi alloy layer formed on the surface of the untreated copper foil is formed by plating. As a cobalt ion supply source of the plating solution, one kind or a mixture of two or more kinds such as cobalt sulfate and cobalt chloride can be used. Bismuth trichloride can be used as a bismuth ion supply source for the plating solution.
The total amount of cobalt content in the Co—Bi alloy plating solution is 1 to 60 g / L, preferably 5 to 40 g / L, as cobalt metal. Moreover, the total amount of bismuth content is 0.5-30 g / L, Preferably it is 2-20 g / L.

The pH of the plating solution in this embodiment is preferably adjusted to 4 to 10, preferably 6 to 8, by adding acid or alkali.
In the plating treatment, an untreated copper foil is subjected to cathode (cathode) electrolysis in a plating solution containing cobalt and bismuth. Current density, 0.05~10A / dm ² is preferred. If the current density exceeds this, gas generation becomes intense and electrodeposition of inevitable impurities occurs, which is not preferable.
The thickness of the Co—Bi film thus obtained is preferably 0.05 to 5 mg / dm ^2, and if this thickness is exceeded, the electrical conductivity decreases, which is not preferable. More preferably 0.1~4mg / dm ^2.

Next, the untreated copper foil provided with the Co—Bi alloy is heat treated in an air atmosphere at 50 ° C. to 300 ° C. for 30 seconds to 5 hours. By performing the heat treatment, a Cu—Bi alloy layer is formed of Cu and Bi on the surface of the copper foil.
Next, a cobalt layer is provided on the surface of the Cu-Bi alloy layer. The formation of the cobalt layer is the same as the conditions formed by plating on the surface of the zinc layer.

The Co—In alloy layer formed on the surface of the untreated copper foil is formed by plating. As a cobalt ion supply source of the plating solution, one kind or a mixture of two or more kinds such as cobalt sulfate and cobalt chloride can be used. As an indium ion supply source of the plating solution, indium methanesulfonate can be used.
The total amount of cobalt content in the Co—In alloy plating solution is 5 to 200 g / L, preferably 20 to 60 g / L, as cobalt metal. The total amount of In content is 1 to 80 g / L, preferably 5 to 40 g / L.

The pH of the plating solution in this embodiment is preferably adjusted to 7 to 11, preferably 8 to 10, by adding acid or alkali.
In the plating treatment, an untreated copper foil is subjected to cathode (cathode) electrolysis in a plating solution containing cobalt and indium. Current density, 0.05~10A / dm ² is preferred. If the current density exceeds this, gas generation becomes intense and electrodeposition of inevitable impurities occurs, which is not preferable.
The thickness of the Co—In film thus obtained is preferably 0.05 to 5 mg / dm ^2, and if it exceeds this thickness, the electrical conductivity is lowered, which is not preferable. More preferably 0.1~4mg / dm ^2.

Next, the untreated copper foil provided with the Co—In alloy is heat-treated in an air atmosphere at 50 ° C. to 300 ° C. for 30 seconds to 5 hours. By performing the heat treatment, a Cu—In alloy layer is formed of Cu and In on the surface of the copper foil.
Next, a cobalt layer is provided on the surface of the Cu—In alloy layer. The formation of the cobalt layer is the same as the conditions formed by plating on the surface of the zinc layer.

Embodiment 1
An embodiment 1 of the copper foil of the present invention will be described in detail with reference to FIGS.
As shown in FIG. 1, a Co—Zn alloy layer 2 is formed on the surface of the untreated copper foil 1.
Next, the copper foil provided with the Co—Zn alloy layer 2 is heat-treated. By heat treatment, the copper foil surface and Zn are alloyed to form a Cu—Zn alloy layer 11, and the surface becomes a Co layer or a Co—Zn layer 12.

  FIG. 2 shows a plating apparatus for forming a Co—Zn alloy layer 2 having a Zn concentration gradient. The untreated copper foil 1 is guided to a plating tank 4 through a guide roll 8 and an electrode roll 3. The untreated copper foil 1 is first subjected to the first stage alloy plating at the anode 6 in FIG. 2, and then the second stage alloy plating is performed at the anode 7 to obtain a surface-treated foil having a Zn concentration gradient. Applied.

An example which performs Co-Zn plating with the plating apparatus of FIG. 2 is shown.
The plating bath composition (plating solution) 5 of the plating tank 4 is cobalt sulfate: cobalt concentration; 50 g / L),
Zinc sulfate: zinc concentration; 1.0 g / L),
Ammonium sulfate: 10g

First, the current density of the anode 6 in FIG. 2 is set to 0.2 A / dm ^2, and first-stage alloy plating is performed with a processing time of 6 seconds. Subsequently, the current density of the anode 7 is set to 2.0 A / dm ^2. A second stage alloy plating is performed with a treatment time of 6 seconds to produce a surface-treated foil having a Zn concentration gradient.
When a plating solution having the above plating bath composition is used, an alloy film having a high Co or Zn content is formed when the current density is low (about 0.05 to 0.3 A / dm ² ), and the current density is high (about 1 An alloy film having a low Zn content of 0.0 to 3.0 A / dm ² ) is formed.

Concentration gradient by performing two-stage plating at a current density different from 0.05 to 0.3 A / dm ² for the first stage current density and 1.0 to 3.0 A / dm ² for the second stage current density. An alloy film having the following can be formed.
The current density and plating time are adjusted according to the desired amount of Co and Zn deposited, the Zn content in the plating film, and the Zn concentration on the plating surface.
In addition, it is preferable that processing time shall be 1 second-20 seconds in each process.
In this embodiment, the plating process is performed in two stages in one (industrially preferable) plating tank, but it is needless to say that a plurality of plating tanks may be provided and processed in three or more stages.

Note that the presence or absence of Zn concentration and Zn concentration gradient on the surface treatment layer surface can be analyzed by Auger electron spectroscopy (AES) in the depth direction from the treatment surface to determine the concentration distribution.
AES measurement conditions: Equipment used Model 680 made by ULVAC-PHI
Acceleration voltage 10 keV
Sputtering rate Oxide film part 2nm / min
Metal part 10nm / min (until Cu peak rises)

  Next, the untreated copper foil 1 provided with the Co—Zn alloy layer 2 is heat-treated at a temperature of 300 ° C. or lower. By performing the heat treatment, a Cu—Zn alloy layer 11 is formed of Cu and a Co—Zn alloy on the surface of the copper foil, and the outermost layer becomes a Co layer or a Co—Zn layer 12. Note that since the heat treatment is performed at 300 ° C. or lower, the reaction of the Cu—Co alloy does not occur.

Embodiment 2
A Zn layer is formed on the surface of the untreated copper foil 1. The Zn layer is subjected to cathode (cathode) electrolysis of an untreated copper foil in a Zn-containing plating solution. Current density, 0.1~1A / dm ² is preferred. The thickness of the zinc coating thus obtained is preferably 0.01 to ² mg / dm ^2, and if this thickness is exceeded, it takes only a long time for Zn-Cu alloying in the subsequent heat treatment. In addition, the electrical resistance increases, and when it is made into a battery, it causes heat generation. More preferably 0.05 to 1 mg / dm ^2.
Next, a Co layer or a Co—Zn layer is provided over the Zn layer. The plating conditions are processed according to the following examples. Next, the copper foil provided with the Co layer or the Co—Zn layer is heat-treated at a temperature of 300 ° C. or lower. By performing the heat treatment, a Cu—Zn alloy layer is formed by the Cu and Zn layers on the surface of the copper foil, and a Co layer or a Co—Zn layer is formed as the outermost layer.

The surface-treated copper foil described above is used as a current collector, and an active material is provided on the surface thereof to form a negative electrode for a Li battery. The active material is applied to the surface of the current collector, and is deposited through drying and pressing processes. The surface-treated copper foil of the present invention can be prevented from softening in this process and is stronger than conventional copper foil. Therefore, when used as a battery, it withstands expansion and contraction of the active material and improves battery cycle characteristics. it can.
In particular, when manufacturing a sheet-type Li battery, the sheets are laminated and processed by hot pressing, so by having an alloy layer whose surface hardness is harder than copper, it is possible to adhere to the active material uniformly with pressure. And a lithium battery negative electrode with good adhesion can be produced. As a matter of course, since the outermost layer is a cobalt layer or a cobalt-low melting point metal alloy layer, copper can be prevented from melting during overdischarge.

  As described above, since the copper foil surface of the present invention is covered with a Cu-low melting point metal alloy layer, the copper foil of the present invention has a hard characteristic compared to a normal copper foil. It is hard to become a habit. Therefore, it is easy to handle the copper foil during battery production, and has a characteristic that the shape does not collapse after the active material is formed.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Electrolytic copper foil production>
Using a Ti plate with Rz = 1.5 μm by buffing as a cathode, an untreated electrolytic copper foil having a thickness of 12 μm was produced in the following plating bath and conditions.
Using the prepared untreated electrolytic copper foil, a Zn coating, a Co coating, or a Co alloy coating was formed under the conditions shown in each example.

<Example 1>
A Co—Zn alloy plating layer having a concentration gradient was surface-treated with the apparatus shown in FIG.
(Plating bath composition)
Cobalt sulfate heptahydrate: Cobalt concentration 50 g / L
Zinc sulfate: Zinc concentration 1.0 g / L
Ammonium sulfate: 10g
(Plating conditions)
Liquid temperature: 40 ° C
pH: 6
Using this plating solution
First stage current density: 0.3 A / dm ² , treatment time 20 seconds Second stage current density: 3.0 A / dm ² , treatment time 20 seconds Co—Zn is applied to the electrolytic copper foil with the above plating solution and plating conditions. An alloy layer was provided.
The formed Co—Zn alloy layer had a Zn content of 7%, a Co deposition amount of 4.8 mg / dm ² , and a Zn concentration gradient (concentration difference) of 7%.
Subsequently, the surface-treated copper foil was heated in an air atmosphere at 150 ° C. within 5 minutes, and Zn was diffused into copper to form a Zn—Cu alloy layer. The Zn content in the Zn—Cu alloy layer was 0.9%.

<Example 2>
Surface treatment was performed with the apparatus shown in FIG.
First stage current density: 0.25 A / dm ² , treatment time 11 seconds Second stage current density: 2.5 A / dm ² , treatment time 11 seconds The Zn content of the Co—Zn alloy attached to the copper foil is The amount of Co adhesion was 2.2 mg / dm ² , and the Zn concentration gradient (concentration difference) was 6%.
Next, the copper foil was heated in the same manner as in Example 1 to form a Zn—Cu alloy layer. The Zn content in the Zn—Cu alloy layer was 0.7%.

<Example 3>
Surface treatment was performed using the same plating solution as in Example 1.
First stage current density: 0.2 A / dm ² , treatment time 8 seconds Second stage current density: 2.0 A / dm ² , treatment time 8 seconds The Zn content of the Co—Zn alloy attached to the copper foil is The Co adhesion amount was 1.1 mg / dm ² , and the Zn concentration gradient (concentration difference) was 5%.
Next, the copper foil was heated in the same manner as in Example 1 to form a Zn—Cu alloy layer. The Zn content in the Zn—Cu alloy layer was 0.5%.

<Example 4>
Surface treatment was performed using the same plating solution as in Example 1.
First stage current density: 0.15 A / dm ² , treatment time 4 seconds Second stage current density: 1.5 A / dm ² , treatment time 4 seconds The Zn content of the Co—Zn alloy attached to the copper foil is The Co adhesion amount was 0.45 mg / dm ² and the Zn concentration gradient (concentration difference) was 4%.
Next, the copper foil was heated in the same manner as in Example 1 to form a Zn—Cu alloy layer. The Zn content in the Zn—Cu alloy layer was 0.3%.

<Example 5>
Surface treatment was performed using the same plating solution as in Example 1.
First stage current density: 0.05 A / dm ² , treatment time 1 second Second stage current density: 1.0 A / dm ² , treatment time 1 second Zn content of the Co—Zn alloy attached to the copper foil is The Co adhesion amount was 0.05 mg / dm ² , and the Zn concentration gradient (concentration difference) was 3%.
Next, the copper foil was heated in the same manner as in Example 1 to form a Zn—Cu alloy layer. The Zn content in the Zn—Cu alloy layer was 0.1%.

<Example 6>
A Zn film was formed on the surface of the electrolytic copper foil under the following conditions.
(Plating bath composition)
Zinc sulfate: Zinc concentration 10g / L
Sodium hydroxide: 100 g / L
(Plating conditions)
Liquid temperature: 25 ° C
Current density: 1.0 A / dm ²
Treatment time: 3 seconds The amount of Zn deposited on the copper foil was 0.20 mg / dm2.
Next, the surface-treated copper foil was heated in a nitrogen atmosphere at 150 ° C. within 5 minutes. Thereby, Zn diffused into the copper foil, and a Zn—Cu alloy layer was formed. The Zn content in the Zn—Cu alloy layer was 0.9%.

Subsequently, a cobalt film was provided under the following conditions, washed with water and dried.
(Co plating bath composition)
Cobalt sulfate heptahydrate: 20 g / L as cobalt metal
Citric acid: 80 g / L
(Plating conditions)
Liquid temperature: 50 ° C
Current density: 5 A / dm ²
Treatment time: 20 seconds The amount of Co adhering to the obtained copper foil was 4.9 mg / dm ² .

<Example 7>
In the same process as in Example 6, surface treatment and heating were performed using the same plating solution as in Example 6. The Zn content in the Zn—Cu alloy layer was 0.7%.
Current density of Zn plating: 0.8 A / dm ² , treatment time 2 seconds Current density of Co plating: 5.0 A / dm ² , treatment time 9 seconds Co adhesion amount attached to copper foil is 2.3 mg / dm ² The amount of deposited Zn was 0.10 mg / dm ² .

<Example 8>
In the same process as in Example 6, surface treatment and heating were performed using the same plating solution as in Example 6. The Zn content in the Zn—Cu alloy layer was 0.5%.
Current density of Zn plating: 0.5 A / dm ² , treatment time 2 seconds Current density of Co plating: 5.0 A / dm ² , treatment time 4 seconds Co adhesion amount attached to the copper foil was 1.1 mg / dm ² Yes, the amount of deposited Zn was 0.07 mg / dm ² .

<Example 9>
In the same process as in Example 6, surface treatment and heating were performed using the same plating solution as in Example 6. The Zn content in the Zn—Cu alloy layer was 0.3%.
Current density of Zn plating: 0.2 A / dm ² , processing time 3 seconds Current density of Co plating: 2.5 A / dm ² , processing time 3 seconds Co adhesion amount attached to the copper foil was 0.40 mg / dm ² The amount of deposited Zn was 0.04 mg / dm ² .

<Example 10>
In the same process as in Example 6, surface treatment and heating were performed using the same plating solution as in Example 6. The Zn content in the Zn—Cu alloy layer was 0.1%.
Current density of Zn plating: 0.1 A / dm ² , time 1 second Current density of Co plating: 1.0 A / dm ² , treatment time 1 second The amount of Co attached to the copper foil is 0.05 mg / dm ² The amount of deposited Zn was 0.007 mg / dm ² .

<Example 11>
The same surface treatment as in Example 3 was performed on the rolled copper foil. The Zn content of the Co—Zn alloy adhered to the copper foil was 11%, the Co adhesion amount was 1.10 mg / dm ² , and the Zn concentration gradient (concentration difference) was 5%.
The copper foil was heated in the same manner as in Example 1 to form a Zn—Cu alloy layer. The Zn content in the Zn—Cu alloy layer was 0.5%.

<Example 12>
A Co—Sn alloy film having a concentration gradient on the surface of the electrolytic copper foil was formed under the following conditions.
(Plating bath composition)
Cobalt chloride hexahydrate: Cobalt concentration 75g / L
Stannous chloride: tin concentration 30g / L
Sodium pyrophosphate: 200 g / L
(Plating conditions)
Liquid temperature: 30 ° C
pH: 7
First stage current density: 0.2 A / dm ² , treatment time 8 seconds Second stage current density: 2.0 A / dm ² , treatment time 8 seconds Using this plating solution, a surface-treated electrolytic copper foil was applied. The Sn content of the deposited Co—Sn layer was 15%, the Co deposition amount was 1.0 mg / dm ² , and the Sn concentration gradient (concentration difference) was 3%.
Subsequently, the surface-treated copper foil was heated in an air atmosphere at 150 ° C. within 5 minutes. Thereby, Sn diffused into Cu by heat, and a Sn—Cu alloy layer was formed. The Sn content in the Sn—Cu alloy layer was 0.5%.

<Example 13>
A Co—Bi alloy film having a concentration gradient on the surface of the electrolytic copper foil was formed under the following conditions.
(Plating bath composition)
Cobalt chloride hexahydrate: Cobalt concentration 20 g / L
Bismuth trichloride: bismuth concentration 5g / L
Sodium citrate: 120 g / L
(Plating conditions)
Liquid temperature: 50 ° C
pH: 7
First stage current density: 0.2 A / dm ² , treatment time 8 seconds Second stage current density: 2.0 A / dm ² , treatment time 8 seconds Using this plating solution, a surface-treated electrolytic copper foil was applied. The Bi content of the deposited Co—Bi layer was 15%, the Co deposition amount was 1.0 mg / dm ² , and the Bi concentration gradient (concentration difference) was 3%.
Subsequently, the surface-treated copper foil was heated in an air atmosphere at 150 ° C. within 5 minutes. Thereby, Bi diffused into Cu by heat, and a Bi—Cu alloy layer was formed. The Bi content in the Bi—Cu alloy layer was 0.5%.

<Example 14>
A Co-In alloy film having a concentration gradient on the surface of the electrolytic copper foil was formed under the following conditions.
(Plating bath composition)
Cobalt methanesulfonate: Cobalt concentration 75g / L
Indium methanesulfonate: Indium concentration 20 g / L
Methanesulfonic acid: 80 g / L
Sodium citrate: 120 g / L
(Plating conditions)
Liquid temperature: 30 ° C
pH: 9
First stage current density: 0.2 A / dm ² , treatment time 8 seconds Second stage current density: 2.0 A / dm ² , treatment time 8 seconds Using this plating solution, a surface-treated electrolytic copper foil was applied. The In content of the deposited Co—In layer was 4%, the Co deposition amount was 1.0 mg / dm ² , and the In concentration gradient (concentration difference) was 3%.
Subsequently, the surface-treated copper foil is heated in an air atmosphere at 150 ° C. within 5 minutes. Thereby, In diffused into Cu by heat, and an In—Cu alloy layer was formed. The In content in the In—Cu alloy layer was 0.5%.

  The copper foil surface-treated in Examples 1 to 14 was kneaded with a graphite-based active material and a water-dispersed styrene-butadiene rubber-based binder, carboxymethyl cellulose as a thickener, and distilled water as a solvent to form a slurry, and coated with copper foil. Then, drying was performed at 110 ° C. for 3 hours, roll pressing was performed, vacuum drying was performed to deposit an active material to form a negative electrode, and a Li battery incorporating the negative electrode was assembled to obtain various evaluation samples.

<Reference Example 1>
In the same process as in Example 1, surface treatment was performed using the same plating solution as in Example 1.
First stage current density: 0.3 A / dm ² , treatment time 26 seconds Second stage current density: 3.0 A / dm ² , treatment time 26 seconds The Zn content of the Co—Zn alloy adhered to the copper foil is The amount of Co adhesion was 5% and 6.0 mg / dm ² .
Next, the copper foil was heated in the same manner as in Example 1 to form a Zn—Cu alloy layer. The Zn content in the Zn—Cu alloy layer was 1.1%.
An active material similar to that of the example was deposited on the surface-treated copper foil to form a negative electrode, a Li battery incorporating the electrode was assembled, and used as an evaluation sample.

<Reference Example 2>
A Li battery was assembled by using the same treated foil as in Example 3 as a current collector and an electrode prepared using an organic binder as the active material binder as a negative electrode, and used as an evaluation sample.

<Comparative example 1>
The untreated electrolytic copper foil was not subjected to surface treatment.

<Comparative example 2>
The untreated electrolytic copper foil was subjected to chromate treatment under the following conditions.
CrO ₃ : 1g / L
Temperature: 20 ° C
Immersion time: 10 seconds

<Comparative Example 3>
The untreated electrolytic copper foil was subjected to rust prevention treatment under the following conditions.
Benzotriazole (BTA): 5 g / L
Temperature: 20 ° C
Immersion time: 10 seconds

  An active material similar to that of the example was deposited on the surface-treated copper foil of each comparative example to form a negative electrode, a Li battery incorporating the electrode was assembled, and used as an evaluation sample.

Measurement means, measurement conditions (1) Measurement of cobalt adhesion amount (content) Analysis was performed with fluorescent X-rays (ZSX Primus manufactured by Rigaku Corporation, analysis diameter: 35φ). The results are listed in Table 1.

(2) Measurement of active material adhesion (peel strength) Graphite-based active material and water-dispersed styrene butadiene rubber binder, carboxymethyl cellulose as a thickener, and distilled water as a solvent are kneaded into a slurry, and coated with copper foil surface Then, drying was performed at 110 ° C. for 3 hours, roll pressing was performed, and vacuum drying was further performed. A resin tape having an adhesive strength of 560 g / cm is applied to the carbon material-coated surface of this material, and the peel strength is measured based on a 90-degree peel test (JIS K 6854-1) when the copper foil is peeled off. It was. The results are also shown in Table 1.

(3) Measurement of conductivity Conductivity was measured based on JIS H 0505. The results are also shown in Table 1.

(4) Measurement of tensile strength Based on IPC standard TM-650, first, the copper foil before the surface treatment was cut into a width of 10 mm, and the tensile strength was measured. Next, the copper foil of each Example, Reference Example, and Comparative Example was cut to a width of 10 mm, and the tensile strength was measured in the same manner. Thereafter, the rate of increase in tensile strength was calculated from the difference between the measured tensile strength values before and after the surface treatment, and summarized in Table 1.

(5) Charging / discharging cycle (battery cycle) characteristic measurement The charging / discharging cycle characteristic is 1 mol / L LiN (CF3SO2) 2 / EC: DEC (1: 1) as an electrolyte, and metallic lithium is used as a counter electrode, and a separator is used. The negative electrode of each example, reference example and comparative example was placed, a CR2032-type coin battery was produced in a dry room, and measured in a voltage range of 0 to 1 V vs. Li / Li + in a high temperature bath at 25 ° C. .
The first cycle was charged / discharged at 0.1 mA / cm ² and the second and subsequent cycles were charged / discharged at 0.2 mA / cm ² . After repeating this cycle for 200 cycles, the battery capacity at the time of initial charge is maintained at 95% or more, ◎, maintained at 94% to 92%, △, maintained at 91% to 89%, and maintained at 88% or less. Is X, and the results are also shown in Table 1.

As shown in Table 1, all the electrical conductivity of Examples 1 to 14 is 95% or more, the battery cycle is also maintained to 92% or more, and satisfactory results are obtained. In particular, the copper foil of the example having a low Co content has a conductivity (IACS) of 98% or more, and heat generation of the conductor due to electric resistance is small, and as a result, it can be determined that the battery cycle characteristics are good.
In each example, as the cobalt content decreases, the adhesion with the active material decreases, the conductivity increases, and the tensile strength tends to decrease. Thus, although cobalt content affects electrical conductivity, adhesiveness with an active material, and tensile strength, all the target conditions were satisfied in the range of each Example.

Since Reference Example 1 had a high cobalt content and decreased electrical conductivity, the evaluation criteria of the present invention could not be satisfied. However, it is a surface-treated foil that has no practical problem as a high-strength foil.
In Reference Example 2, there was a problem in wettability with an active material using an organic binder, and the battery characteristics did not satisfy the evaluation criteria of the present invention. However, as shown in Example 3, the water dispersion binder was satisfactory. The result is obtained.
As is clear from Example 3 and Reference Example 2, when the binder is in an aqueous dispersion, the wettability between the cobalt surface and the active material deposited thereon is good and the negative electrode is satisfactory. Both binders were unfavorable for the binder, and the result was unsatisfactory as a negative electrode.

On the other hand, in Comparative Example 1, since the surface treatment is not performed, the conductivity is satisfactory, but the battery cycle is not satisfactory.
Comparative Example 2 has a slightly inferior adhesion to the active material due to the presence of chromium on the surface, and it is not satisfactory as the intended foil, such as the need to consider environmental issues because of the use of chromium. there were.

  In Comparative Example 3, an organic rust preventive layer is provided on the surface. The copper foil surface of the present invention is a Co-containing layer, and from the viewpoint of good water wettability between the Co layer and the water-based binder, the battery characteristics are better when using the water-based binder than when using the organic binder. It is shown that.

  As described above, the present invention covers an untreated copper foil surface with a Co layer or a Co-low melting point metal alloy layer, and therefore there is no layer containing hexavalent chromium, and is an environmentally friendly electrode material. Moreover, it is possible to provide a current collector (copper foil) capable of maintaining excellent charge / discharge cycle life characteristics and a high battery capacity at the beginning of charging, and to provide a Li battery using the current collector.

1. 1. Untreated copper foil Co-Zn alloy layer3. Zn layer4. Co / Co—Zn layer 11. Cu—Zn alloy layer 12. Co / Co—Zn layer 21. Untreated copper foil 22. Guide roll 23. Electrode roll 24. Plating layer 25. Plating solution 26. Anode 27. Anode 28. Guide roll

Claims (11)

  A lithium secondary battery current collector in which an alloy layer of a low melting point metal and copper is provided on at least one surface of the untreated copper foil, and a cobalt layer or an alloy layer of cobalt and a low melting point metal is provided thereon. Copper foil for body.   The copper foil for a lithium secondary battery current collector according to claim 1, wherein the metal having a low melting point is a metal having a melting point of 500 ° C. or less.   The copper foil for a lithium secondary battery current collector according to claim 2, wherein the metal having a low melting point is zinc, tin, bismuth or indium.   The lithium secondary battery current collector according to claim 1, wherein the alloy layer of the metal having a low melting point and the copper is a Zn-Cu alloy layer, and the zinc content in the Zn-Cu alloy layer is 1 wt% or less. Copper foil for body.   An alloy layer of cobalt and a metal having a low melting point is applied to at least one surface of the untreated copper foil by electrolytic plating, and the copper foil provided with an alloy layer of cobalt and a metal having a low melting point is heat-treated, and copper is applied to the surface of the copper foil. And a method for producing a copper foil for a lithium secondary battery current collector, wherein an alloy layer of a metal having a low melting point is formed.   A metal having a low melting point is plated on at least one surface of the untreated copper foil, a cobalt layer is plated on the metal having the low melting point, and then the copper foil having the metal having the low melting point and the cobalt layer is heat-treated. The manufacturing method of the copper foil for lithium secondary battery collectors which forms the alloy layer of Cu and a metal with low melting | fusing point on the copper foil surface.   A metal having a low melting point is plated on at least one surface of the untreated copper foil, and a copper foil subjected to the metal having a low melting point is heat-treated to form an alloy layer of Cu and a metal having a low melting point on the copper foil surface, Then, the manufacturing method of the copper foil for lithium secondary battery collectors which coats a cobalt layer on it.   The method for producing a copper foil for a lithium secondary battery current collector according to any one of claims 5 to 7, wherein the metal having a low melting point is zinc, tin, bismuth or indium.   The lithium alloy according to any one of claims 5 to 7, wherein the alloy layer of the low melting point metal and copper is a Zn-Cu alloy layer, and the zinc content in the Zn-Cu alloy layer is 1 wt% or less. A method for producing a copper foil for a secondary battery current collector.   A copper foil produced by the copper foil according to claim 1 or the production method according to any one of claims 5 to 9 as a current collector, and for a lithium secondary battery in which an active material is deposited on the current collector Negative electrode.   A lithium secondary battery using the negative electrode of claim 10 as a negative electrode.

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