BACKGROUND

Technical Field

The present disclosure relates to a method and an apparatus for producing an electrolytic aluminum foil with which a high-quality electrolytic aluminum foil can be efficiently obtained.

Background Art

In recent years, lithium ion batteries have been utilized as batteries for automobiles and personal computers, and the positive electrode current collectors thereof are generally aluminum foils.

A conventional aluminum foil is produced by rolling a foil base. As the thickness of an aluminum foil which can be used as a positive electrode current collector of a lithium ion battery, about 10 μm is the lower limit at the level of current rolling techniques. However, to increase the battery capacity of a lithium ion battery further and miniaturize the lithium ion battery, it is required to make an aluminum foil thinner and reduce the volume of a positive electrode current collector in the inner volume of the battery, and instead fill a larger amount of an active material. Specifically, an aluminum foil having a thickness of 5 to 10 μm is desired. In addition, it is desired that an aluminum foil have better mechanical properties than conventional aluminum foils as the thickness is made thinner. Even though such an aluminum foil can be produced by a rolling method, there has been a problem that the number of rolling steps needs to be increased and the production cost thereby becomes relatively expensive.

On the other hand, according to an electrolysis method, an aluminum foil having a thickness of 5 to 10 μm can be produced through a few steps. In producing a high-quality aluminum foil by the electrolysis method, establishment of a method for controlling the purity in an electrolytic bath is desired. In addition, to reduce the production cost, it is preferable to use an anode made of aluminum having a purity as low as possible. For example, in Japanese Patent Application Laid-Open No. 4-337097, a method for electroplating an aluminum or an aluminum alloy on a base substance metal, wherein the aluminum and a plating bath are brought into contact in a reaction tank separated from a plating tank is described. In addition, in Japanese Patent Application Laid-Open No. 2004-269950, there is described a method for producing an electrolytic copper foil, the method including treating an electrolytic solution with activated carbon and using the activated carbon-treated electrolytic solution.

However, the method of Japanese Patent Application Laid-Open No. 4-337097 adopts a method of trapping an impurity in the reaction tank after the impurity which has dissolved from the anode diffuses in the whole plating tank, and therefore there is a problem that part of the diffused impurity is mixed in depositing aluminum from the plating bath. In addition, according to the method of Japanese Patent Application Laid-Open No. 2004-269950, a component in the electrolytic solution can be adsorbed by activated carbon, but an impurity other than aluminum cannot be adsorbed and removed selectively, and therefore the method of Japanese Patent Application Laid-Open No. 2004-269950 is not effective in production of an electrolytic aluminum foil.

SUMMARY

Thus, the present disclosure has been completed in consideration of the circumstances, and the present disclosure provides a production method and a production apparatus with which an impurity which has dissolved from an anode can be effectively trapped and removed and a high-quality electrolytic aluminum foil can be efficiently obtained without using a high-purity (for example, 99.99% or more) aluminum anode.

Solution to Problem

(1) A method for producing an electrolytic aluminum foil, the method comprising: supplying an electrolytic solution in an electrolytic cell provided with a diaphragm between an anode and a cathode; and depositing an aluminum foil on a surface of the cathode by electrolysis, wherein the diaphragm is made of aluminum having a purity of 85.0% or more and has a plurality of pores having an average pore diameter of 100 to 1000 μm.

(2) The method for producing an electrolytic aluminum foil according to (1), wherein the diaphragm is made of aluminum having a purity of 85.0% to 99.90%.

(3) The method for producing an electrolytic aluminum foil according to (1), wherein the diaphragm is prepared by mixing and sintering an aluminum powder and a substance for forming pores and thereafter removing the substance for forming pores.

(4) The method for producing an electrolytic aluminum foil according to (1), wherein the electrolytic solution is a molten salt containing: an alkylimidazolium halide or an alkylpyridinium halide and an aluminum halide.

(5) The method for producing an electrolytic aluminum foil according to (1), wherein the electrolytic solution is a molten salt containing: an alkylimidazolium chloride or an alkylpyridinium chloride and aluminum chloride.

(6) The method for producing an electrolytic aluminum foil according to (1), wherein the cathode is made of titanium; and the anode is made of aluminum having a purity of 95.0 to 99.9%.

(7) An apparatus for producing an electrolytic aluminum foil, the apparatus comprising: an electrolytic cell in which an electrolytic solution is supplied; an anode and a cathode each to be immersed in the electrolytic solution; and a diaphragm provided between the anode and the cathode, and depositing an aluminum foil on a surface of the cathode by electrolysis, wherein the diaphragm is made of aluminum having a purity of 85.0% or more and has a plurality of pores having an average pore diameter of 100 to 1000 μm.

According to the present disclosure, an impurity which has dissolved from an anode can be effectively trapped and removed and a high-quality electrolytic aluminum foil can be efficiently obtained without using a high-purity (for example, 99.99% or more) aluminum anode.

