JP2013077462A - COPPER FOIL FOR Li BATTERY COLLECTOR, ELECTRODE FOR Li BATTERY USING THE SAME, AND Li BATTERY - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a copper foil for negative electrode collector (electrode material) capable of maintaining excellent charge and discharge cycle life characteristic and high battery capacity at early charge as electrode material for Li battery and manufacturing therefor, and to provide rust prevention without using chrome by eliminating an adverse effect of environmental pollution due to hexavalent chromium from environmental problems.SOLUTION: The copper foil for battery collector is structured by forming an alloy layer of low-melting metal and copper on a surface of at least one side of unprocessed copper foil and then forming an alloy layer of a nickel layer or nickel and the low-melting metal thereon. Preferably, the low-melting metal is Zn, Bi, or In.

Description

The present invention relates to a copper foil as a current collector for a Li battery (lithium ion secondary 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.

As the negative electrode active material, a carbon powder having an average particle size of about 20 μm, artificial graphite, natural graphite, coke and the like dispersed in a solvent together with a binder and slurried are used. After the liquid is applied to a copper foil, it is dried. Further, it is molded by roll pressure bonding to a thickness of about several tens of μm to obtain a negative electrode. Usually, organic PVDF (polyvinylidene fluoride) is used as the binder, and NMP (normal methylpyrrolidone) is used as the solvent.
In addition, Sn-based alloys, Si-based alloys, metal nitrides, Sn—O compounds, Si—O compounds, and the like have been researched and developed as active materials other than carbon.

As the copper foil for the negative electrode current collector, a copper foil having a thickness of about 8 to 20 μm is mainly used at present, but in recent years, the thinning of the copper foil used for increasing the capacity of the battery has progressed.
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.

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.

Patent Document 1 (Japanese Patent Laid-Open No. 8-306390) discloses a copper foil for preventing the occurrence of pinholes as a copper foil for a negative electrode current collector of a non-aqueous electrolyte secondary battery using an active material using a binder. A copper foil provided with a nickel coating or chromium coating of 1 μm or more is proposed. In particular, the nickel coating is expected to maintain the initial capacity even after an overdischarge state.
By the way, in recent years, the thickness of the copper foil used for the Li battery is required to be 12 μm or less. However, even if a nickel coating or a chromium coating is applied on such a thin copper foil, the surface hardness of the copper foil is not improved at all, and when manufacturing the negative electrode of the battery, the copper foil (current collector) becomes a habit. It often happens that problems are inferior in workability.

Patent Document 2 (Patent No. 4107004) discloses a negative electrode current collector made of rolled copper foil having a chromium-based film formed on its surface for the purpose of effectively preventing elution of the copper foil during battery overdischarge. Proposals to make are made. Although the Ni film is also mentioned in this proposal, the amount of Ni adhesion is not specified.
In order to effectively prevent elution of copper foil, as suggested in Patent Document 1, a thickness of 1 μm or more is considered necessary. The electrical resistance of nickel is higher than that of copper, and if the amount of nickel deposited is too large, it will cause heat generation, and there is a concern that the cycle characteristics will be remarkably deteriorated when it is used for the negative electrode current collector of a battery.
In addition, since it is difficult to produce a copper foil having a thickness of 12 μm or less by rolling, an electrolytic copper foil is employed as the negative electrode of the Li battery as the copper foil having a thickness of 12 μm or less.

  In Patent Document 3 (Japanese Patent Laid-Open No. 7-192767), when a copper foil is used as a negative electrode current collector, the elution of copper into the electrolytic solution is suppressed and the charge / discharge cycle characteristics are improved. It is proposed that nickel plating is applied, and as an effect thereof, it is disclosed that the carbon layer (which seems to be an active material layer) is difficult to peel off from the copper foil during the charge / discharge cycle and has excellent charge / discharge cycle characteristics. However, in this proposal, since the nickel layer is directly provided on the copper foil, the electric resistance increases depending on the amount of nickel deposited. Further, it is presumed that it becomes difficult to maintain the shape as a negative electrode when a battery is formed, and it seems difficult to produce a negative electrode for a Li battery with good cycle characteristics.

JP-A-8-306390 Japanese Patent No. 4107004 JP 7-192767 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 present invention is an environment-friendly electrode material because there is no layer containing hexavalent chromium on the surface of the copper foil, and the above characteristics are improved compared to organic rust prevention treatment. And providing a current collector (copper foil) that is environmentally friendly and that is capable of maintaining excellent charge / discharge cycle life characteristics and a high battery capacity at the beginning of charging by using such a material. An object is to provide a Li battery using a body.

The copper foil for a Li battery current collector of the present invention is provided with an alloy layer of a low melting point metal and copper on at least one surface of an untreated copper foil, and a nickel layer or an alloy layer of nickel and a low melting point metal thereon. Is provided.
The low melting point metal is preferably Zn, Bi, or In.

  Preferably, the low melting point metal is Zn, and the Zn content of the Zn—Cu alloy layer is 1 wt% or less.

  In the method for producing a copper foil for a Li battery collector of the present invention, an alloy layer of Ni and a low-melting metal is applied to at least one surface of an untreated copper foil by electrolytic plating, and an alloy layer of Ni and a low-melting metal Is a manufacturing method in which a copper foil subjected to heat treatment is heat treated at 300 ° C. or lower to form an alloy layer of Cu and a low melting point metal on the surface of the copper foil.

  In the method for producing a copper foil for a Li battery current collector of the present invention, a low melting point metal layer is plated on at least one surface of an untreated copper foil, and a Ni layer is plated on the low melting point metal layer. Then, a manufacturing method in which a copper foil having a low melting point metal layer and a Ni layer is heat-treated at 300 ° C. or lower to form an alloy layer of Cu and a low melting point metal on the surface of the copper foil.

  Moreover, the manufacturing method of the copper foil for Li battery collectors of the present invention is such that the low melting point metal layer is plated on at least one surface of the untreated copper foil, and the copper foil having the low melting point metal layer is 300 ° C. or less. A manufacturing method in which an alloy layer of Cu and a low-melting-point metal is formed on the surface of the copper foil by heat treatment, and then a Ni layer is plated thereon.

  The low melting point metal is preferably Zn, Bi or In.

The negative electrode for a Li battery of the present invention is an electrode 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 active material preferably uses an aqueous dispersion binder for the binder.

  The Li battery of the present invention is a battery using the negative electrode.

Since the surface of the copper foil of the present invention is coated with a Ni layer or a Ni alloy layer, discoloration resistance and adhesion between the negative electrode active material without using chemicals that affect the environment such as hexavalent chromium. It is possible to provide a copper foil for a Li battery electrode that satisfies both requirements.
Moreover, this invention can provide the high performance Li battery which is excellent in charging / discharging cycle life.

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 ion 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 copper foil for Li battery electrodes 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 nickel layer or an alloy layer of Ni and a low melting point metal thereon. Zn, Bi, In or the like is used as the low melting point metal.
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, due to the remaining rolling oil, the decrease in the adhesion of the active material and the nickel-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.

In the present invention, a low melting point metal such as Zn, Bi, In or the like is provided on an untreated copper foil surface, a low melting point metal-containing copper alloy layer is formed by the low melting point metal and the copper foil surface, and a nickel layer provided thereon Ni adhesion amount is suppressed as much as possible, copper foil elution is prevented, and electrical resistance is not increased 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 metal and copper, and the Ni layer is a film that suppresses the Ni adhesion amount as much as possible. As a result, it becomes a hard foil, and the property that the copper foil does not easily become wrinkles appears. 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. Moreover, it becomes an excellent copper foil as a current collector for a Li battery negative electrode having 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, it is preferable to employ Zn as the low melting point metal and to make the Zn content of the Zn—Cu alloy layer 1 wt% or less.
The Zn content is 1 wt% or less in order to suppress the decrease in conductivity of the copper foil as much as possible, and the conductivity compared to Cu is 95% together with the thickness of the Ni layer (including the Ni 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—Ni alloy layer is provided on the surface of the untreated copper foil to a thickness of 0.05 to 5 mg / dm ² by electrolytic plating. Next, the copper foil coated with the Ni—Zn alloy layer is subjected to heat treatment in an air atmosphere at 50 ° C. to 300 ° C. for 30 seconds to 5 hours. With this heat treatment, Zn in the Ni—Zn alloy is thermally diffused into Cu on the surface of the copper foil and alloyed.
In addition, when plating the Ni-Zn alloy on the copper foil surface, the Zn concentration in the Ni-Zn alloy layer is high because the Zn is easily dissolved in the acid by plating in two stages. The slope can be lowered as the distance from the copper foil surface increases. The gradient rate is preferably 10% or less.

Thus, the surface of the untreated copper foil was coated with a Zn—Ni alloy layer having a Zn concentration gradient to a thickness of 0.05 to 5 mg / dm ² , and then the copper foil coated with the Ni—Zn alloy layer was coated with 50 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 by heat treatment in an air atmosphere at ℃ to 300 ℃ for 30 seconds to 5 hours.
In the above description, the Zn—Ni alloy layer is provided on the surface of the copper foil. However, it is also possible to provide a Zn layer on the surface of the copper foil and then provide a Ni 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 Ni layer thereon.

Thus, by providing a Zn layer or a Ni—Zn alloy layer on the surface of the copper foil, oxidation corrosion of the copper foil during atmospheric heating can be prevented, and a Zn—Cu alloy layer with few impurities can be formed. 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, since the heat treatment temperature is set to 300 ° C. or lower, a Ni—Cu alloy is not formed.
The reason why the Ni—Cu alloy layer is not formed on the outermost layer of the copper foil is that the outermost layer is the Ni surface, and the surface is wetted with the slurry of the active material using the water dispersion binder. Property is remarkably improved, and the adhesiveness with the binder is greatly improved as compared with the conventional copper foil.

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 added with an alkali such as sodium hydroxide and dissolved in a solution to obtain 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. Exceeding the Zn content is not preferable because the Zn content may be 1 wt% or more due to thermal diffusion with the copper foil surface.

In this embodiment, the nickel layer is formed by plating. As a nickel ion supply source of the plating solution, one or a mixture of two or more of nickel sulfate, nickel chloride, nickel carbonate and the like can be used.
The total amount of nickel content in the nickel plating solution is 5 to 200 g / L, preferably 10 to 100 g / L, as nickel metal.

The pH of the plating solution is adjusted to 0.5 to 6.0, preferably 2.0 to 5.0 by adding acid or alkali.
In the plating process, a Zn-treated copper foil is subjected to cathode (cathode) electrolysis in a nickel-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 nickel 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. Is not preferable. More preferably 0.1~4mg / dm ^2.
The amount of nickel in the nickel-containing film can be measured by a fluorescent X-ray method or a method of obtaining the whole copper foil by an atomic absorption method.

The nickel-zinc alloy layer formed on the surface of the untreated copper foil is formed by plating. As a nickel ion supply source of the plating solution, one or a mixture of two or more of nickel sulfate, nickel chloride, nickel carbonate and the like 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 nickel content in the Ni—Zn alloy plating solution is 5 to 200 g / L, preferably 20 to 60 g / L, as nickel 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 in 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, the untreated copper foil is subjected to cathode (cathode) electrolysis in a nickel and zinc-containing plating solution. 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 Ni—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 copper foil described above will be described with reference to FIGS.
Embodiment 1
As shown in FIG. 1, a Ni—Zn alloy layer 2 is formed on the surface of the untreated copper foil 1.
An example of the film forming conditions of the Ni—Zn alloy layer 2 having a concentration gradient will be described using the plating apparatus shown in FIG.
The untreated copper foil 21 is guided to the plating tank 24 through the guide roll 8 and the electrode roll 3. The plating bath composition (plating solution) 25 of the plating solution 24 is nickel sulfate (nickel concentration: 50 g / L), zinc sulfate (zinc concentration: 1.0 g / L), and ammonium sulfate: 10 g.
Using this plating solution 25, first, the current density of the anode 26 in FIG. 2 is set to 0.2 A / dm ^2, and the first stage alloy plating is performed with a processing time of 6 seconds. Is 2.0 A / dm ^{2 and a} second stage alloy plating is performed in a treatment time of 6 seconds to produce a surface-treated foil having a Zn concentration gradient.
When the plating solution having the plating bath composition is used, an alloy film having a high Zn content is formed when the current density is low (about 0.05 to 0.3 A / dm ² ), and the current density is higher (about 1. An alloy film having a low Zn content of 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 Ni and Zn deposited, the Zn content in the plating film, and the Zn concentration on the plating surface.
In addition, 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 Ni—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 by Cu and Ni—Zn alloy on the surface of the copper foil, and the outermost surface becomes the Ni layer or the Ni—Zn layer 12. Note that since the heat treatment is performed at 300 ° C. or lower, the reaction of the Cu—Ni alloy does not occur.

Embodiment 2
A Zn layer 3 is formed on the surface of the untreated copper foil 1. The Zn plating layer electrolyzes the 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 Ni layer or a Ni—Zn layer 4 is provided on the Zn layer 2. The plating conditions are processed according to the following examples. Next, the copper foil 1 provided with the Ni layer or the Ni—Zn layer 4 on the Zn 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 by the Cu and Zn layers on the surface of the copper foil, and a Ni layer or a Ni—Zn layer 12 is formed on the outermost surface.

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. Of course, since Ni plating is performed, it is possible to prevent the copper from melting during overdischarge.

  As described above, the copper foil of the present invention is characterized by the fact that the surface of the untreated copper foil is covered with a Cu-low metal alloy layer, so that it has a hard characteristic compared to a normal copper foil. It is hard to become. 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.
Plating bath;
Copper sulfate pentahydrate 280 g / L,
Sulfuric acid 100g / L,
Chlorine ion 35ppm
7 ppm low molecular weight gelatin with an average molecular weight of 3000,
Hydroxyethyl cellulose 3 ppm,
1-ppm sodium 3-mercapto-1-propanesulfonate
Foil deposition conditions,
Electrolyte temperature: 55 ° C
Flow rate: 0.3 m / min,
Current density: 50A / dm2
Using the prepared untreated electrolytic copper foil, a Zn coating, a Ni coating, or a Ni-containing alloy coating was formed under the conditions shown in each example.

<Example 1>
A Ni—Zn alloy plating layer having a concentration gradient was formed using the apparatus shown in FIG.
(Plating bath composition)
Nickel sulfate: Nickel concentration 50g / L
Zinc sulfate: Zinc concentration 1.0 g / L
Ammonium sulfate: 10g
(Plating conditions)
Liquid temperature: 40 ° C
pH: 6
Using this plating solution, with the apparatus shown in FIG.
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 Ni—Zn is applied to the electrolytic copper foil under the above plating solution and plating conditions. An alloy layer was provided.
The formed Ni—Zn alloy layer had a Zn content of 7%, a Ni adhesion amount of 4.9 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.

<Example 2>
Surface treatment was performed using the same plating solution as in Example 1.
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 Ni—Zn alloy adhered to the copper foil is The amount of adhesion of Ni was 2.1 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.

<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 6 seconds Second stage current density: 2.0 A / dm ² , treatment time 6 seconds The Zn content of the deposited Ni—Zn alloy is 11%, The Ni adhesion amount was 0.90 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.

<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 Ni—Zn alloy attached to the copper foil is 12%, Ni adhesion amount was 0.45 mg / dm ² , and 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.

<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 Ni—Zn alloy attached to the copper foil is The Ni 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.

<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.

Subsequently, a nickel film was provided under the following conditions, washed with water and dried.
(Ni plating bath composition)
Nickel sulfate hexahydrate: 40 g / L as nickel metal
Boric acid: 30 g / L
Sodium hypophosphite: 8 g / L
(Plating conditions)
Liquid temperature: 30 ° C
pH; 4
Current density: 3 A / dm ²
Treatment time: 20 seconds The amount of Ni adhering to the obtained copper foil was 5.0 mg / dm ² .

<Example 7>
Surface treatment and heating were performed using the same plating solution as in Example 6.
Current density of Zn plating: 0.8 A / dm ² , treatment time 2 seconds Current density of Ni plating: 2.5 A / dm ² , treatment time 11 seconds The amount of Ni attached to the copper foil was 2.1 mg / dm ² The amount of deposited Zn was 0.10 mg / dm ² .

<Example 8>
Surface treatment and heating were performed using the same plating solution as in Example 6.
Current density of Zn plating: 0.5 A / dm ² , treatment time 2 seconds Current density of Ni plating: 2.0 A / dm ² , treatment time 6 seconds The amount of Ni attached to the copper foil was 0.90 mg / dm ² Yes, the amount of deposited Zn was 0.07 mg / dm ² .

<Example 9>
Surface treatment and heating were performed using the same plating solution as in Example 6.
Current density of Zn plating: 0.2 A / dm ² , treatment time 3 seconds Current density of Ni plating: 1.5 A / dm ² , treatment time 4 seconds The amount of Ni attached to the copper foil was 0.45 mg / dm ² . The amount of deposited Zn was 0.04 mg / dm ² .

<Example 10>
Surface treatment and heating were performed using the same plating solution as in Example 6.
Current density of Zn plating: 0.1 A / dm ² , time 1 second Current density of Ni plating: 1.0 A / dm ² , treatment time 1 second The amount of Ni 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 Ni—Zn alloy attached to the copper foil was 11%, the amount of Ni attached was 0.90 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.

<Example 12>
A Ni—Sn alloy film having a concentration gradient on the surface of the electrolytic copper foil was formed under the following conditions.
(Plating bath composition)
Nickel chloride: Nickel 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 10 seconds Second stage current density: 2.0 A / dm ² , treatment time 10 seconds Using this plating solution, surface treated electrolytic copper foil The Sn content of the deposited Ni—Sn layer was 15%, the Ni deposition amount was 0.90 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.

<Example 13>
A Ni—In alloy film having a concentration gradient on the surface of the electrolytic copper foil was formed under the following conditions.
(Plating bath composition)
Nickel chloride: Nickel concentration 75g / L
Indium chloride: Indium concentration 40 g / L
Hydrochloric acid: 80 g / L
(Plating conditions)
Liquid temperature: 30 ° C
First stage current density: 0.2 A / dm ² , treatment time 10 seconds Second stage current density: 2.0 A / dm ² , treatment time 10 seconds Using this plating solution, surface treated electrolytic copper foil The deposited Ni—In layer had an In content of 4%, an Ni deposition amount of 0.90 mg / dm ² , and an In concentration gradient (concentration difference) of 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.

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

<Comparative example 2>
Surface treatment was performed using the same plating solution as in Example 1.
First stage current density: 0.3 A / dm ² , treatment time 30 seconds Second stage current density: 3.0 A / dm ² , treatment time 30 seconds Zn content of the Ni—Zn alloy attached to the copper foil is 5% and the Ni adhesion amount was 6.0 mg / dm ² .

<Comparative Example 3>
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 4>
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

<Comparative Example 5>
The same treated foil as in Example 3 was used, and an organic binder was used as the active material binder.

Measurement means, measurement conditions (1) Measurement of metal 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 Graphite-based active material and water-dispersed styrene-butadiene rubber-based binder, carboxymethyl cellulose as a thickener, and distilled water as a solvent are kneaded and slurried, and coated on a copper foil surface at 110 ° C. For 3 hours, followed by roll pressing and further vacuum drying. 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 the IPC standard TM-650, first, the tensile strength of a copper foil cut to a width of 10 mm before the surface treatment is measured. Next, using the same copper foil, the copper foils of Examples 1 to 13 and Comparative Examples 1 to 5 were each cut to a width of 10 mm, and the tensile strength was measured in the same manner. Thereafter, the difference in tensile strength measured before the surface treatment was summarized in Table 1 as the rate of increase in tensile strength.

(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 electrodes of Examples 1 to 13 and Comparative Examples 1 to 5 were arranged, CR2032-type coin batteries were 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. did.
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 95% or more, ◎, 92% or more ○, 89% or more △, otherwise X, and the results are also shown in Table 1. did.

The electric conductivity of Examples 1 to 13 is all 95% or more, the battery cycle is also maintained to 92% or more, and satisfactory results are obtained. In particular, in Examples 3 and 8, since the Ni content is small, the conductivity (IACS) of the Zn-Cu alloyed copper foil is 98% or more, and the heat generation of the conductor due to electric resistance is small, resulting in battery cycle characteristics. Is judged good.
In each example, as the nickel content decreases, the adhesion with the active material decreases, and conversely, the conductivity increases. However, the tensile strength tends to decrease. As described above, the nickel content affects the electrical conductivity, the adhesion to the active material, and the tensile strength, but all the target conditions are satisfied within the range of each example.

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.
Since the comparative example 2 has much nickel content, electrical conductivity falls, As a result, it heat | fever-generates in a charging / discharging cycle test, and becomes a thing which cannot satisfy a battery cycle.
Comparative Example 3 was unsatisfactory as the intended foil because of the presence of chromium on the surface and poor adhesion to the active material, and the tensile strength did not increase.

In Comparative Example 4, an organic rust preventive layer is provided on the surface. The copper foil surface of the present invention is a Ni-containing layer, and from the viewpoint of good water wettability between the Ni layer and the aqueous binder, the battery characteristics are superior when using an aqueous binder than when using an organic binder. It is shown that.
In Comparative Example 5, since an organic binder was used as the binder of the active material, a peeling phenomenon occurred between the nickel surface in the charge / discharge cycle test, and the battery cycle was not satisfactory.

  In the above embodiment, a gradient is particularly provided in the Zn concentration. By providing a gradient in the Zn concentration, alloying of the Zn—Cu alloy by heat treatment can be easily performed. For example, alloying is performed by heat treatment at 150 ° C. within 5 minutes, whereas alloying is not performed by heat treatment at 150 ° C. for 5 minutes when the Zn concentration on the surface of Cu is increased without providing a gradient of Zn concentration. An alloy layer can be formed by a heat treatment of 5 minutes or longer, but a uniform layer may not be obtained. As a result, the heat generation of the conductor due to electric resistance is large, and the battery cycle characteristics are deteriorated as compared with the examples.

  As described above, the present invention covers the surface of the copper foil with the Ni layer or the Ni-low melting point metal alloy layer, so that there is no layer containing hexavalent chromium, and it is an environmentally friendly electrode material. A current collector (copper foil) capable of maintaining excellent charge / discharge cycle life characteristics and a high battery capacity at the beginning of charge can be provided, and a Li battery using the current collector can be provided.

1. 1. Untreated copper foil Ni-Zn alloy layer3. Zn layer4. Ni / NI-Zn layer 11. Cu—Zn alloy layer 12. Ni / NI-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 (10)

  Copper foil for Li battery current collector in which an alloy layer of low melting point metal and copper is provided on at least one surface of the untreated copper foil, and a nickel layer or an alloy layer of nickel and low melting point metal is provided thereon .   The copper foil for a Li battery current collector according to claim 1, wherein the low melting point metal is Zn, Bi, or In.   The copper foil for a Li battery current collector according to claim 1, wherein the alloy layer of the copper and the low melting point metal is a Zn-Cu alloy layer, and the Zn content in the Zn-Cu alloy is 1 wt% or less.   An alloy layer of Ni and a low melting point metal is applied to at least one surface of the untreated copper foil by electrolytic plating, and the copper foil on which the alloy layer of Ni and a low melting point metal is applied is heat-treated at 300 ° C. or less, and the copper foil surface The manufacturing method of the copper foil for Li battery electrical power collectors which forms the alloy layer of Cu and a low melting-point metal in the inside.   A low-melting point metal layer is plated on at least one surface of the untreated copper foil, a Ni layer is plated on the low-melting point metal layer, and then the low-melting point metal layer and the copper foil with the Ni layer are 300 ° C. or less The manufacturing method of the copper foil for Li battery collectors which heat-processes by and forms the alloy layer of Cu and a low melting metal on the copper foil surface.   A low melting point metal layer is plated on at least one surface of the untreated copper foil, and the copper foil with the low melting point metal layer is heat-treated at 300 ° C. or lower to form an alloy layer of Cu and a low melting point metal on the copper foil surface. A method for producing a copper foil for a Li battery current collector, which is formed and then a Ni layer is plated thereon.   The method for producing a copper foil for a Li battery current collector according to any one of claims 4 to 6, wherein the low melting point metal is Zn, Bi or In.   The Li battery current collector according to claim 4, wherein the alloy layer of copper and a low-melting-point metal is a Zn—Cu alloy layer, and the Zn content in the Zn—Cu alloy is 1 wt% or less. A method for producing body copper foil.   The negative electrode for Li battery which made the collector the copper foil of the said Claim 1, or the copper foil manufactured by the manufacturing method in any one of Claims 4-8, and deposited the active material on this collector .   A Li battery using the negative electrode of claim 9 as a negative electrode.

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