JP2011222672A - Perforated conductive foil and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a perforated conductive foil which is used in place of a perforated copper foil, i.e. a collector for the negative electrode of a lithium ion capacitor, and exhibits electrical characteristics comparable to those of the perforated copper foil and yet much more lighter and economical than the perforated copper foil.SOLUTION: An aluminum foil 50 is subjected to chemical etching or electrolytic etching to obtain an aluminum foil 51 in which many through holes 52 are formed while being scattered. A plurality of layers of different kinds of metal film 60 consisting of materials different from the aluminum foil are laminated on a surface of the perforated aluminum foil 51 thus obtained. The different kinds of metal film 60 are a substitution layer 61 consisting of Zn or a Zn alloy, a resistive layer 62 consisting of Ni or a Ni alloy, and an electroplated Cu layer 63 sequentially from inside.

Description

  The present invention relates to a multi-layer perforated conductive foil in which Cu is coated on the outermost surface of a base material made of an aluminum foil formed by dispersing a number of fine through-holes, and is used as a negative electrode current collector in a lithium ion capacitor. The present invention relates to a suitable perforated conductive foil and a method for producing the same.

  Electrochemical elements such as lithium ion secondary batteries and electric double layer capacitors that are small and light, have high energy density, and can be repeatedly charged and discharged are rapidly expanding their demands by utilizing their characteristics. Lithium ion secondary batteries have a relatively high energy density and are therefore used in fields such as mobile phones and notebook personal computers. Electric double layer capacitors are used as memory backup compact power sources for personal computers and the like. In addition, since electric double layer capacitors are excellent in rapid charge / discharge characteristics, their use in construction machines such as excavators and cranes that require repeated charge / discharge has become full-scale.

  On the other hand, the energy density of the electric double layer capacitor is about 3 to 4 Wh / l, which is about two orders of magnitude smaller than that of the lithium ion secondary battery. For this reason, with the aim of achieving both high energy density and charge / discharge speed, the development of a lithium ion capacitor that combines a lithium ion battery for the negative electrode and an electric double layer capacitor for the positive electrode out of the positive electrode and the negative electrode has been promoted. Yes. This lithium ion capacitor combines safety, high capacity, and rapid charge / discharge, and is highly expected as a new electrochemical device. However, it has not yet been widely used in general. One of the reasons is pre-doping described below.

  FIG. 3 shows the relationship between the lithium ion secondary battery, the electric double layer capacitor, and the lithium ion capacitor, and FIG. 4 schematically shows the basic structure of the lithium ion capacitor. Moreover, the conceptual diagram of the single cell in a lithium ion capacitor is shown in FIG.

  As shown in FIG. 3, the basic structure of the lithium ion capacitor uses a positive electrode of an electric double layer capacitor as a positive electrode and a negative electrode of a lithium ion secondary battery as a negative electrode. As shown in FIG. 4, the positive electrode 10 and the negative electrode 20 are wound via a separator 30 or have a laminated structure in which they are alternately laminated. Hereinafter, the former is referred to as a wound laminated structure, and the latter planar thin film laminated type is referred to as a planar laminated structure. The positive electrode 10 corresponding to the positive electrode of the electric double layer capacitor is generally obtained by coating the surface of a current collector 11 made of aluminum foil with activated carbon or the like as the positive electrode active material 12. Generally, the negative electrode 20 corresponding to the negative electrode of the lithium ion secondary battery is obtained by coating the surface of a current collector 21 made of copper foil with carbon or the like as the negative electrode active material 22.

  In such a lithium ion capacitor, in order to obtain high performance, it is necessary to dope lithium ions into the negative electrode active material 22 from the lithium supply source 40 such as lithium foil in advance in the final stage before shipment. This operation is so-called pre-doping, but the process takes a long time, and it is difficult to uniformly dope the negative electrode active material 22, and this pre-doping problem is the practical application of the lithium ion capacitor. This is one of the factors that inhibit

  As a countermeasure for solving the pre-doping problem in the lithium ion capacitor, a method of forming a large number of fine through holes in the current collectors 11 and 21 is generally used (Patent Document 1). In the lithium ion capacitor using the perforated current collectors 11 and 21 having a large number of fine through holes as the positive electrode 10 and the negative electrode 20, the lithium ions supplied from the lithium supply source 40 during pre-doping are the current collector 11. , 21 can pass through the positive electrode 10 and the negative electrode 20. Therefore, even if the positive electrode 10 and the negative electrode 20 are wound laminated structure lithium ion capacitors wound through the separator 30 or planar laminated structure lithium ion capacitors, they are separated from the lithium supply source 40. The negative electrode 20 at the place can also be doped with lithium ions.

  However, the following problems associated with forming through holes in the current collector 21 of the negative electrode 20 contribute to hindering the practical use and generalization of lithium ion capacitors. That is, the copper foil is used for the current collector 21 of the negative electrode 20 as described above. As a method of forming a large number of through-holes in copper foil, for example, an expanded metal method in which a staggered array of cuts is made in a metal foil, and this cut is expanded to form a mesh, or a punching method in which holes are opened by reciprocating movement of a needle A mechanical method such as a rotating roll punching method that opens a hole by passing a metal foil along a roll with a large number of needles on the surface is common, but in the expanded metal method, after forming a through hole There is a problem in the flatness of the copper foil, and in the punching method, there is a problem in the flatness because burrs are generated around the through hole.

  Further, in such a mechanical method, since the copper foil needs to have a corresponding mechanical strength, it is difficult to reduce the thickness of the metal foil, and the weight reduction is hindered. Although burrs are also removed by press working or roll processing, if the thickness of the metal foil is reduced, wrinkles and the like are generated in the processing, so that application is difficult when the thickness is thin.

  Due to such problems, Patent Document 2 proposes forming through holes by a chemical method that is not a mechanical method. This method includes a step of attaching a synthetic resin layer on one surface of a metal foil via an adhesive layer, a step of forming a resist layer having a predetermined pattern on the other surface of the metal foil, and forming on the other surface. Etching the resist layer as a mask to form a plurality of through holes in the metal foil from the other surface side, forming the through holes, and then peeling the synthetic resin layer and the adhesive layer from the metal foil And a step of removing the resist layer after peeling the synthetic resin layer and the adhesive layer.

  The chemical method by chemical etching is considered to be an excellent method in that there is no burr or return by the mechanical punching method, but the number of steps is complicated and the cost may increase. . Further, in the process of peeling the laminated polypropylene film to prevent etching, wrinkles may occur because the metal foil is thin, and there is a problem in workability.

  As still another method by chemical etching, Patent Document 3 and Patent Document 4 propose a technique using a photographic method. In this method, a photosensitive resin is applied on both sides of a copper foil, and ultraviolet rays are exposed on one side through a predetermined negative film and a positive film. Subsequently, by performing development, etching of the metal foil, and removal of the resist, a metal foil having a through hole can be formed. This is an excellent method in that the hole diameter of the through hole can be adjusted by changing the specifications of the negative film and the positive film. However, since the chemical etching method is used, the number of steps is large as in the method of Patent Document 2 described above, and the economic efficiency is poor.

  As a recent trend, the number of stacked positive electrode members, negative electrode members and separators (the number of windings in the winding structure) has increased remarkably due to an increase in battery capacity, and as a result, the member area has increased. As a result, the increase in size, weight, and cost of the battery are problematic. This is no exception in lithium ion capacitors, and therefore, there is a demand for light and inexpensive positive and negative electrode members.

Japanese Patent Laid-Open No. 8-1007048 JP 2008-41511 A JP 2000-294250 A Japanese Patent Laid-Open No. 11-67217

  The present invention is used in place of a perforated copper foil which is a current collector for a negative electrode of a lithium ion capacitor and exhibits electrical characteristics comparable to a perforated copper foil, and is lighter than that perforated copper foil. An object is to provide an inexpensive perforated conductive foil and a method for producing the same.

  In order to reduce the size and weight of the lithium ion capacitor, the present inventors have focused on electrode members, particularly the negative electrode current collector. That is, the positive electrode current collector in a lithium ion capacitor is a perforated foil of aluminum having a small specific gravity, whereas the negative electrode current collector is a perforated foil of copper having a large specific gravity. Although these current collectors are being made thinner, on the other hand, since the number of stacked layers (the number of turns in a wound laminated structure) is increasing, the total area of the current collectors is also increasing. As a result, the weight ratio of the negative electrode current collector made of perforated copper foil is still large, which is one factor that hinders the weight reduction of the negative electrode current collector.

  In order to reduce the weight of the negative electrode current collector, the present inventors examined the effectiveness of a multi-layer perforated conductive foil having a perforated aluminum foil as a base material and coated with copper on the surface thereof. . As a result, it was confirmed that the perforated conductive foil of the composite structure functions without any problem as a negative electrode current collector in a lithium ion capacitor and that the aluminum base material is reduced in weight. Moreover, it has been found that this composite perforated conductive foil is less expensive than perforated copper foil, even considering the cost of copper coating on the surface of the aluminum foil.

  That is, the aluminum foil has a lower mechanical strength than the copper foil, and when the thickness is small, mechanical drilling is difficult. For this reason, a chemical method is mainly used for drilling the aluminum foil, and chemical etching and electrolytic etching are well known as chemical methods. Electrolytic etching is a method in which a metal foil to be drilled is connected to an anode, carbon is connected to a cathode, and electricity is supplied in an acidic solution. The metal foil is selectively dissolved, and a large number of fine through holes are formed. By controlling the energization amount, the temperature of the acidic liquid, the immersion time, etc., the hole diameter of the through hole can be adjusted. Since this method is simple and does not generate burrs, it is used for drilling aluminum foil, which is a current collector for an anode of a lithium ion capacitor. However, this electrolytic etching cannot be used for drilling copper foil. Moreover, when using it for the punching process of aluminum foil, special and expensive raw material foil is needed.

  On the other hand, chemical etching requires many steps as is well known, so it is more expensive than electrolytic etching. However, aluminum foil that can be used for chemical etching is less expensive than aluminum foil that can be used for electrolytic etching. Therefore, the total cost of etching is slightly more expensive than chemical etching.

  On the other hand, the material cost of aluminum foil is much lower than that of copper foil. On the other hand, the cost of the copper coating on the surface of the aluminum foil is comparable to the cost of chemical etching. As a result, even if the cost of copper coating on the surface of the aluminum foil is taken into consideration, the total cost of the composite perforated conductive foil is lower than the total cost of the perforated copper foil.

  The perforated conductive foil of the present invention has been completed on the basis of such knowledge, and is made of a material different from aluminum foil on one or both sides of a perforated aluminum foil formed by dispersing a plurality of through holes. A feature of the constitution is that a layer or a plurality of layers of dissimilar metal films are laminated and coated, and the outermost metal layer of the dissimilar metal film has a laminated structure made of Cu.

  In addition, the method for producing a perforated conductive foil of the present invention includes a step of dispersing and forming a plurality of through holes in an aluminum foil, a step of replacing the surface of the perforated aluminum foil with Zn or a Zn alloy, and Zn or Zn. The method includes a step of electrolessly plating Ni or a Ni alloy on the replacement film of the alloy, and a step of electroplating Cu on the plating film of the Ni or Ni alloy.

  The basic concept of the perforated conductive foil of the present invention and the manufacturing method thereof is shown in FIG. 1 in comparison with the case of a conventional perforated copper foil. In the perforated conductive foil and the method for producing the same of the present invention, aluminum means both pure aluminum and an aluminum alloy.

  In the case of a perforated copper foil, a perforated copper foil 71 is manufactured from a copper foil 70 without a hole by a punching method, a lath method, or a chemical etching method. The weight per hit is also large. On the other hand, in the case of the perforated conductive foil and the manufacturing method thereof according to the present invention, a perforated aluminum foil 51 is first prepared from the aluminum foil 50 having no holes, and one or more layers whose outermost surface is Cu are formed on the surface. A different kind of metal film 60 is laminated and coated. A punching method or a lath method can be used as a method for producing the perforated aluminum foil 51. However, in consideration of flatness, a chemical etching method or an electrolytic etching method is preferable. From the viewpoint of material cost, versatility, and ease of control of hole specifications. Chemical etching is preferable, and electrolytic etching is preferable from the viewpoint of man-hours. Then, the surface of the perforated aluminum foil 51 is covered with one or more layers of dissimilar metal films 60 whose outermost layer is made of Cu, so that the multilayer perforated conductive foil is produced by a chemical etching method. It has the same electrochemical function as the perforated copper foil and is cheaper and lighter than the perforated copper foil.

That is, in the production of the perforated conductive foil of the present invention, since plating is repeated after the drilling process, the manufacturing man-hours and production costs are slightly increased compared to the case of the perforated copper foil, but the base material is aluminum. It is lightweight, and the base material cost is low. As a whole, both weight and cost are small. Incidentally, the true specific gravity of the aluminum foil is 2.7 g / cm ^3, which is 1/3 or less of the true specific gravity of the copper foil (8.6 g / cm ³ ). The material cost of the aluminum foil is about 1/10 in the case of chemical etching and about 1/5 in the case of electrolytic etching, compared with the material cost of the copper foil.

  The perforated conductive foil of the present invention is suitable as a current collector for a negative electrode of a lithium ion capacitor. In that case, the metal film needs to be coated on both surfaces of the aluminum foil, and it is preferable to interpose an intermediate film made of Ni or Cr as a resistance layer between the aluminum foil and the outermost Cu film. Regardless of the application, it is preferable to replace a very thin region on the surface of the aluminum foil with Zn or a Zn alloy. Although the surface of the aluminum foil is covered with an oxide film and metal plating is difficult, this metal plating is facilitated by forming a substitution layer made of Zn or a Zn alloy.

  In the case of a perforated conductive foil used as a negative electrode current collector of a lithium ion capacitor, the thickness is preferably 1 to 100 μm, particularly preferably 5 to 50 μm. When the thickness of the perforated conductive foil is too large, the thickness of the current collector is increased, and the miniaturization of the lithium ion capacitor is hindered. However, if the thickness is too small, there is a risk that the carrying function as a current collector is lost. In addition, the handleability is lowered, and the plating work is difficult. The effectiveness of the present invention is remarkable in the case of a thickness of 20 μm or less, particularly 15 μm or less, which makes it difficult to apply a mechanical method to the production of a perforated metal foil.

  The shape of the through hole may be any shape such as a circle, an ellipse, a rectangle, a diamond, and a slit, but a circle, an ellipse, and a rectangle are preferable. Regardless of the hole shape, the through holes need not have the same size and the same shape in the thickness direction of the conductive foil, and may have different sizes and different shapes. In the formation of through-holes by chemical etching, the hole shape, hole diameter, distribution state, etc. can be arbitrarily controlled. The through-holes formed by electrolytic etching are generally round holes and are dispersed with a uniform distribution throughout the aluminum foil.

  The hole diameter of the through hole is preferably 10 to 300 μm, where the opening area is represented by the diameter of a round hole having the same area. If the pore diameter is too small, the permeation of lithium ions to be doped in advance and the diffusion of the electrolyte solution will not be performed smoothly. On the other hand, if the pore diameter is too large, problems such as a decrease in mechanical strength and dripping when applying the electrode active material occur. In electrolytic etching of an aluminum foil, the pore diameter can be changed over a wide range by etching conditions and acid treatment after etching.

  The number of through-holes is preferably 10 to 80%, particularly preferably 20 to 60%, expressed by the aperture ratio defined by Equation 1. If the aperture ratio is too small, transmission of lithium ions to be doped in advance and diffusion of the electrolytic solution will not be performed smoothly. On the other hand, when the aperture ratio is too large, a decrease in mechanical strength of the perforated conductive foil becomes a problem.

  As described above, the hole shape of the through hole is not limited, but in a single perforated conductive foil, it is preferable that the hole diameter is the same as the hole diameter, and the distribution density is also uniform.

  Drilling by electrolytic etching is possible for an aluminum foil, but not for a copper foil that is a negative electrode current collector of a lithium ion capacitor. The reason is considered as follows. The crystal structure of aluminum is a face-centered cubic lattice, and the crystal plane formed by the arrangement of atoms can be a densely arranged plane (111) and a sparsely arranged plane (100). When aluminum is etched by electrolytic etching, the crystal state is greatly involved, so that etching is selective. That is, the sparse surface is more easily etched. Aluminum used in the electrolytic etching of the aluminum foil is in such a state that dense surfaces and sparse surfaces are arranged in advance. On the other hand, in the case of Cu, the crystal structure is the same as that of aluminum, but the crystal plane is not uniform and is randomly arranged. Therefore, even if electrolytic etching is performed, the entire Cu surface is only etched without selectivity, so that the result is not like aluminum.

  The perforated conductive foil of the present invention is a perforated metal foil having a composite laminated structure in which Cu is coated on the outermost surface with a perforated aluminum foil having a low material cost as a base material. Compared to foil, the total cost is low and light. Moreover, even if it uses as a negative electrode collector of a lithium ion capacitor, it shows the electrical property which is inferior compared with the conventional perforated copper foil. Therefore, the negative electrode cost of the lithium ion capacitor is reduced, the negative electrode is lightened and the negative electrode is miniaturized. As a result, the production cost of the lithium ion capacitor is reduced, and the large effect is achieved.

  The method for producing a perforated conductive foil according to the present invention produces a perforated metal foil having a composite laminated structure in which Cu is coated on the outermost surface with a perforated aluminum foil having a low material cost as a base material. Compared with the case of manufacturing the perforated metal foil, the total manufacturing cost can be reduced and the weight can be reduced. Moreover, even if it uses as a negative electrode collector of a lithium ion capacitor, the perforated conductive foil of an electrical property comparable to the conventional perforated copper foil can be manufactured. Therefore, the negative electrode cost of the lithium ion capacitor is reduced, the negative electrode is lightened and the negative electrode is miniaturized. As a result, the production cost of the lithium ion capacitor is reduced, and the large effect is achieved.

It is process drawing which shows the basic concept of the perforated conductive foil of this invention, and its manufacturing method compared with the case of the conventional perforated copper foil. It is a schematic diagram which shows the manufacturing process of the perforated conductive foil of this invention in steps. It is a related figure of a lithium ion secondary battery, an electric double layer capacitor, and a lithium ion capacitor. It is a schematic diagram which shows the basic structure of a lithium ion capacitor. It is a conceptual diagram of the single cell in a lithium ion capacitor.

  Hereinafter, an embodiment of the present invention will be described with reference to FIG.

  The perforated conductive foil of the present embodiment is used for a negative electrode current collector of a lithium ion capacitor, and a perforated aluminum foil 51 manufactured from an aluminum foil 50 is used as a base material. This is a perforated metal laminate in which different kinds of metal films 60 made of a plurality of different metal layers are laminated and coated.

  The perforated aluminum foil 51 is a support (support) for the dissimilar metal film 60, and has a large number of through-holes 52 formed by chemical etching or electrolytic etching with a uniform distribution for the permeation of lithium ions in pre-doping. Have. Here, the dissimilar metal film 60 has a three-layer structure including a substitution layer 61 made of Zn or a Zn alloy, a resistance layer 62 made of an electroless Ni plating layer or an electroless Ni alloy plating layer, and an electric Cu plating layer 63. The inner peripheral surface of each through hole 52 in the perforated aluminum foil 51 is also laminated and coated.

  The substitution layer 61 in the dissimilar metal film 60 removes the oxide film formed on the surface of the perforated aluminum foil 51 and enables the resistance layer 62 to be plated. About 0.1 μm.

  The resistance layer 62 made of an electroless Ni plating layer or an electroless Ni alloy plating layer is an electrical resistance layer for causing the perforated conductive foil to function as a negative electrode current collector of a lithium ion capacitor, and the thickness thereof is, for example, 0. 0.03 to 0.5 μm. That is, if there is no electroless Ni plating layer or electroless Ni alloy plating layer between the perforated aluminum foil 51 and the electric Cu plating layer 63, the current flows between the perforated aluminum foil 51 and the electric Cu plating layer 53. Flows in a concentrated manner (current circulates in the negative electrode), making it difficult for the current to flow between the negative electrode and the positive electrode. It becomes difficult to perform the function as the resistance layer in which the thickness of the resistance layer 62 is too small. On the other hand, when the layer thickness is too large, it acts as a resistance layer when electrolytic copper plating is performed, resulting in uneven film thickness of the electroplated copper.

  The electric Cu plating layer 63 is a functional film that gives the perforated aluminum foil 51 a function as a negative electrode current collector of a lithium ion capacitor, and has a thickness of, for example, 1 to 10 μm. If the layer thickness of the electric Cu plating layer 63 is too small, the electrical conductivity will be reduced, and it will be difficult to achieve the battery function without obtaining the original electrical characteristics of copper, and if it is too large, it will be advantageous in terms of weight reduction and low cost. Cannot show gender.

  Next, the manufacturing method of the perforated electrically conductive film used for the negative electrode electrical power collector of a lithium ion capacitor is demonstrated concretely.

1) Process for producing perforated aluminum foil (chemical etching method)
A negative or positive resist is applied to both surfaces of the aluminum foil 50 before drilling, and a predetermined negative or positive mask is superimposed on one surface (surface) and exposed with UV. The entire surface is exposed without using a photomask on the other surface (back surface). Subsequently, the aluminum surface is exposed in a predetermined pattern on the surface by development, and the exposed portion is dissolved and removed with an aluminum etchant such as iron chloride. Subsequently, the resist on the front and back surfaces is removed with a stripping solution using caustic soda or the like. Thus, a perforated aluminum foil 51 in which through holes are formed in a predetermined pattern is obtained. The size, shape, distribution form and the like of the through holes can be changed by the photomask pattern, and the aperture ratio can be arbitrarily adjusted.

(Electrolytic etching method)
The aluminum foil 50 before drilling is connected to the anode, carbon is connected to the cathode, and electrolytic etching is performed in an acidic solution. Hydrochloric acid can be used as the acidic liquid. The diameter of the through hole 52 in the perforated aluminum foil 51 can be adjusted by controlling the energization amount, the temperature of the acidic liquid, and the immersion time. The hole diameter of the through hole 52 can be further increased by treatment with an acidic solution after electrolytic etching.

2) Step of forming a substitution layer made of Zn or a Zn alloy When forming a Ni or Ni alloy layer on the surface of aluminum, the surface of aluminum is substituted with Zn or a Zn alloy, and the oxide film is removed from the surface. In general, a method of electrolessly plating Ni or a Ni alloy thereon is generally used. A typical example of the process is “alkali degreasing → desmutting → Zn or Zn alloy replacement → replacement coating peeling → Zn or Zn alloy replacement → Ni or Ni alloy electroless plating”.

(Alkaline degreasing)
For the purpose of etching and oxidizing the surface of the aluminum foil, the surface is preferably washed with an alkali. As the cleaning liquid, for example, sodium carbonate and tribasic sodium phosphate 20 to 25 g / l or sodium hydroxide aqueous solution 50 g / l is used. In the case of using an aqueous sodium hydroxide solution, the immersion temperature is preferably 50 ° C. to 60 ° C., and the immersion time is preferably 30 seconds to 60 seconds.

(De-smut)
It is preferable to remove smut (black precipitate) formed by impurities in aluminum generated by etching. The smut remover includes, for example, 65% nitric acid 500 ml / l, sulfuric acid 200 ml / l depending on the content of the metal component contained in the aluminum. For example, the immersion temperature when using nitric acid is preferably 10 ° C. to 30 ° C., and the immersion time is preferably 10 seconds to 60 seconds.

(Zn or Zn alloy substitution)
Displacement plating of Zn or Zn alloy is performed on the desmutted Al surface. Examples of the substitution plating solution include a mixed solution of sodium hydroxide 120 g / l, zinc oxide 20 g / l, crystalline ferric chloride 2 g / l, lossel salt 50 g / l, and sodium nitrate 1 g / l. A commercially available Zn or Zn alloy plating solution may also be used. For example, Substar Zn-1, Zn-2, Zn-3, Zn-8, Zn-10, Zn-111, Zn-222, Zn-291 etc. by Okuno Pharmaceutical Co., Ltd. are mentioned. The plating solution is properly used according to the amount of metal impurities in the aluminum foil to be plated. When this solution is used, the immersion temperature is preferably 15 ° C. to 25 ° C., and the immersion time is preferably 15 seconds to 40 seconds.

(Zn or Zn alloy film peeling)
Double substitution can densify the substitution film and improve adhesion and covering power. Therefore, the Zn or Zn alloy layer once coated and substituted is peeled off. As the stripping solution, for example, 65% nitric acid 500 ml / l and the like can be mentioned. The immersion temperature is preferably 15 ° C to 30 ° C, and the immersion time is preferably 20 to 60 seconds.

(Zn or Zn alloy substitution)
Zn or Zn alloy substitution plating is performed again on the surface from which the Zn or Zn alloy layer has been peeled off. Examples of the substitution plating solution include a mixed solution of sodium hydroxide 120 g / l, zinc oxide 20 g / l, crystalline ferric chloride 2 g / l, lossel salt 50 g / l, and sodium nitrate 1 g / l. A commercially available Zn or Zn alloy plating solution may also be used. For example, Substar Zn-1, Zn-2, Zn-3, Zn-8, Zn-10, Zn-111, Zn-222, Zn-291 etc. by Okuno Pharmaceutical Co., Ltd. are mentioned. The plating solution is properly used according to the amount of metal impurities in the aluminum foil to be plated. When this solution is used, the immersion temperature is preferably 15 ° C. to 25 ° C., and the immersion time is preferably 15 seconds to 40 seconds.

3) A step of forming a resistance layer made of Ni or Ni alloy on the substitution layer.
(Ni or Ni alloy plating)
Ni or Ni alloy plating is performed on the substituted Zn or Zn alloy. The Ni or Ni alloy plating to be used is not particularly limited as long as it is a plating solution usually used for electroless plating. For example, as the Ni plating solution, commercially available products can be widely used, and examples thereof include an aqueous solution containing 30 g / l nickel sulfate, 20 g / l sodium hypophosphite, and 50 g / l ammonium citrate. Examples of the Ni alloy plating solution include a Ni—P alloy plating solution in which a phosphorus compound is a reducing agent and a Ni—B plating solution in which a boron compound is a reducing agent. Top Nicolon XT (Okuno Pharmaceutical Co., Ltd.), ICP Nicolon GM (E) (Okuno Pharmaceutical Co., Ltd.), Top Chemialoy B-1 (Okuno Pharmaceutical Co., Ltd.), ICP Nicolon DK (Okuno Pharmaceutical Co., Ltd.) And ICP Nicolone DK (Okuno Pharmaceutical Co., Ltd.) and Top Chemialoy B-1 (Okuno Pharmaceutical Co., Ltd.) are more preferable. As for immersion temperature, 30 to 90 degreeC is preferable. The immersion time is preferably 15 seconds to 10 minutes.

4) Step of performing electric Cu plating on resistance layer The electric Cu plating bath is not particularly limited as long as it is a plating solution generally used. For example, when electroplating Cu, Cu-sulfuric acid 60-110 g / L, sulfuric acid 160-200 g / L and hydrochloric acid 0.1-0.15 mL / L are added to pure water, and Okuno Pharmaceutical Co., Ltd. Top Lucina SF Base WR1z5 -5.0 mL / L, Top Lucina SF-B 0.5-2.0 mL / L and Top Lucina SF leveler 3.0-1010 mL / L may be added as additives. As a preferable Cu plating bath, 70 g / L of sulfuric acid, 200 g / L of sulfuric acid and 0.5 mL / L of hydrochloric acid are added to pure water, and Top Lucina SF base WR 2.5 mL / L, Top Lucina SF-B 1.0 mL / L and Top Lucina SF Add leveler 5.0 mL / L. As for immersion temperature, 20-30 degreeC is preferable. The dipping time depends on the thickness of the Cu film to be plated. For example, when a 2 μm Cu film is to be dipped, it may be dipped for about 5 minutes at a current density of 2 A / dm.

  Between each process of 1) -4), in order to prevent the process liquid of a previous process invading into a next process, you may provide a water washing process.

  Hereinafter, although the example of the present invention is given and explained in more detail, the present invention is not limited to these.

(Electrolytic etching)
An aluminum foil having a thickness of 10 μm was prepared. The aluminum foil was connected to the anode, the carbon electrode was connected to the cathode, and electrolytic etching was performed at 80 ° C. in 5% hydrochloric acid at a current density of 2 A / dm for 1 minute. Subsequently, through holes formed by electrolytic etching were expanded in 60 ° C. and 5% hydrochloric acid, washed with water and dried to obtain a perforated aluminum foil having a thickness of 10 μm, an average pore diameter of 0.1 mm, and an aperture ratio of 40%.

(Zn substitution and electroless Ni plating)
The resulting perforated aluminum foil was first immersed in a 5% aqueous sodium hydroxide solution adjusted to 50 ° C. for 1 minute, and then immersed in a 30% nitric acid aqueous solution adjusted to 30 ° C. Subsequently, it was immersed in Substar Zn-111 (Okuno Pharmaceutical Co., Ltd.) adjusted to 25 ° C. for 1 minute and subjected to a zincate treatment. Subsequently, in order to peel the zincate film, the film was immersed in a 30% nitric acid aqueous solution adjusted to 30 ° C. for 1 minute, and then immersed in Substar Zn-111 (Okuno Pharmaceutical Co., Ltd.) adjusted to 25 ° C. for 1 minute. Then, it was immersed for 1 minute 30 seconds in Dop Chemia Alloy B1 (Okuno Pharmaceutical Co., Ltd.) adjusted to 50 ° C. to form a 0.02 μm Ni layer and dried at 100 ° C. for 1 hour.

(Electric Cu plating)
The perforated aluminum foil with the Ni layer formed on the surface was connected to the cathode, the insoluble electrode was connected to the anode, and electro Cu plating was performed in a Cu sulfate aqueous solution adjusted to 25 ° C. By immersing for 5 minutes at a current density of 2 A / dm ² , 2 μm of the Cu layer was formed. As a result, a perforated metal laminate having a total thickness of 14 μm in which Cu was laminated on the surface of the aluminum foil was obtained as the perforated conductive foil of the present invention. The obtained perforated metal laminate is free from burrs and wrinkles, and can be used as a negative electrode current collector in a lithium ion capacitor.

(Zn substitution and electroless Ni plating)
The perforated aluminum foil obtained in Example 1 (the average diameter of the through holes was 0.1 mm, the thickness was 10 μm, and the porosity was 40%) was first added to a 5% sodium hydroxide aqueous solution adjusted to 50 ° C. It was immersed for 30 minutes and then immersed in a 30% nitric acid aqueous solution adjusted to 30 ° C. Subsequently, it was immersed in Substar Zn-111 (Okuno Pharmaceutical Co., Ltd.) adjusted to 25 ° C. for 1 minute and subjected to a zincate treatment. Subsequently, in order to peel the zincate film, the film was immersed in a 30% nitric acid aqueous solution adjusted to 30 ° C. for 1 minute, and then immersed in Substar Zn-111 (Okuno Pharmaceutical Co., Ltd.) adjusted to 25 ° C. for 1 minute. Then, it was immersed for 1 minute 30 seconds in Dop Chemia Alloy B1 (Okuno Pharmaceutical Co., Ltd.) adjusted to 50 ° C. to form a 0.02 μm Ni layer and dried at 100 ° C. for 1 hour.

(Electric Cu plating)
The aluminum foil with the Ni layer formed on the surface was connected to the cathode, the insoluble electrode was connected to the anode, and Cu was plated in an aqueous Cu sulfate solution adjusted to 25 ° C. By immersing for 10 minutes at a current density of 2 A / dm 2, 4 μm of the Cu layer was formed. Cu was laminated on the aluminum foil to obtain a metal laminate having a total thickness of 18 μm. The obtained perforated metal laminate is free from burrs and wrinkles, and can be used as a negative electrode current collector in a lithium ion capacitor.

(Chemical etching)
A negative resist solution (Shinwa Kogyo, EF-100) was uniformly applied to an aluminum foil (10 μm) to a thickness of 10 μm with a bar coater and dried at 80 ° C. for 10 minutes. Subsequently, a negative film mask (150 μm) having two 0.1 mm diameter holes in a 0.25 mm square was prepared. The negative film was brought into vacuum contact with one side of the aluminum on which the resist was laminated, and irradiated with 300 mj / cm ² of ultraviolet light from an ultraviolet exposure machine provided at a certain distance from it, thereby forming a latent image on the resist layer. On the other hand, the other surface different from the surface on which the negative film mask was formed and adhered was exposed to 300 mj / cm ² of ultraviolet light without interposing the negative film mask. Subsequently, the unexposed portion was removed by developing with a 1% aqueous sodium carbonate solution at 1 minute / 30 ° C.

Subsequently, the exposed aluminum surface after development was removed by etching. Specifically, a shower treatment was performed with a 2.2 mol / dm ³ FeCl ₃ +1.0 mol / cm ³ HCl aqueous solution (temperature 40 ° C.) for 1 minute at a pressure of 0.15 MPa. After this, it was immediately washed with water and dried. Subsequently, the cured resist was peeled and removed. That is, a shower treatment was performed with a 3% aqueous sodium hydroxide solution (temperature: 40 ° C.) for 1 minute under the condition of 0.15 MPa. Thereafter, washing and drying were performed to obtain a perforated aluminum foil having a thickness of 10 μm and an aperture ratio of 40%.

  The obtained perforated aluminum foil was subjected to Zn substitution, electroless Ni plating and electric Cu plating in the same manner as in Example 1, and a perforated metal laminate having a total thickness of 14 μm in which Cu was laminated on the surface of the aluminum foil. Obtained. The obtained perforated metal laminate is free from burrs and wrinkles, and can be used as a negative electrode current collector in a lithium ion capacitor.

  For the perforated aluminum foil having a thickness of 10 μm and an aperture ratio of 40% obtained by the same chemical etching as in Example 3, Zn substitution, electroless Ni plating and electric Cu plating were performed in the same manner as in Example 2, and the aluminum foil A perforated metal laminate having a total thickness of 18 μm and Cu laminated on the surface was obtained. The obtained perforated metal laminate is free from burrs and wrinkles, and can be used as a negative electrode current collector in a lithium ion capacitor.

Comparative Example 1

A round hole having a hole diameter of 0.3 mm was punched in a copper foil (60 mm × 60 mm) having a thickness of 15 μm at a density of ² per 0.36 mm ² . Burrs occurred on the surface opposite to the punched surface. Rolling was performed to remove the burrs. Then, in order to remove the lubricating oil adhering at the time of rolling, it degreased with 3% sodium hydroxide aqueous solution. A perforated copper foil having a thickness of 14 μm and an aperture ratio of 40% was obtained. However, since the copper foil was thin and wrinkles occurred during processing, it was difficult to use it as a negative electrode current collector in a lithium ion capacitor.

Comparative Example 2

A copper foil having a thickness of 15 μm was prepared. The copper foil was connected to the anode, the carbon electrode was connected to the cathode, and electrolytic etching was performed at 50 ° C. in a 5% sulfuric acid aqueous solution for 1 minute at a current density of 2 A / dm ² . It was difficult to selectively etch the copper foil, and the through hole was not formed only by reducing the thickness of the 15 μm copper foil to 10 μm. For this reason, the use as a negative electrode electrical power collector in a lithium ion capacitor is impossible.

Comparative Example 3

A negative resist solution (Shinwa Kogyo, FE-100) was uniformly applied to a thickness of 10 μm with a bar coater on a copper foil (60 mm × 60 mm) having a thickness of 15 μm, and dried at 80 ° C. for 10 minutes. Subsequently, a negative film mask (150 μm thick) having two 0.1 mm diameter round holes in a 0.25 mm square was prepared. The negative film was vacuum-adhered to one side of the copper foil on which the resist was laminated, and 300 mj / cm ² of ultraviolet light was irradiated from an ultraviolet exposure machine provided at a certain distance from it to form a latent image on the resist layer. . On the other hand, the other surface different from the surface on which the negative film mask was formed and adhered was exposed at 300 mj / cm ² without interposing the negative film mask. Subsequently, the unexposed portion was removed by developing with a 1% aqueous sodium carbonate solution for 1 minute at 30 ° C.

Thereafter, the exposed copper foil surface after development was etched. Specifically, a shower treatment was performed with a 2.2 mol / dm ³ FeCl ₃ +1.0 mol / cm ³ HCl aqueous solution (temperature 40 ° C.) for 1 minute at a pressure of 0.15 MPa. This was followed by immediate water washing and drying. Subsequently, the cured resist was peeled and removed. Specifically, a shower treatment was performed with a 3% aqueous sodium hydroxide solution (temperature: 40 ° C.) for 1 minute at a pressure of 0.15 MPa. Thereafter, washing with water and drying were performed again to obtain a perforated copper foil having a thickness of 14 μm and an aperture ratio of 40%. The obtained perforated copper foil is free from burrs and wrinkles, and can be used as a negative electrode current collector in a lithium ion capacitor.

Evaluation item (adhesion)
Perforated metal laminate of Example 1 (thickness 14 μm) that can be used as a negative electrode current collector in a lithium ion capacitor, Perforated metal laminate of Example 2 (thickness 18 μm), and Perforated of Example 3 With respect to the metal laminate (thickness 14 μm) and the perforated metal laminate (thickness 18 μm) of Example 4, a peel test was performed on dissimilar metal films laminated and coated on the surface of a perforated aluminum foil as a base material. The peeling test was a tape peeling test according to JIS-H8504. The results are shown in Table 1. In any of the perforated metal laminates, separation of all layers of the dissimilar metal film and separation of some layers were not observed.

(conductivity)
Perforated metal laminate of Example 1 (thickness 14 μm) that can be used as a negative electrode current collector in a lithium ion capacitor, Perforated metal laminate of Example 2 (thickness 18 μm), and Perforated of Example 3 The electrical conductivity of the metal laminate (thickness 14 μm), the perforated metal laminate (thickness 18 μm) of Example 4 and the perforated copper foil (thickness 14 μm) of Comparative Example 3 were evaluated. did. The electrical conductivity is the reciprocal of the volume resistance value. In the perforated metal laminates of Examples 1 to 4, the integrity of the dissimilar metal film laminated on the surface of the perforated aluminum foil as the base material and the aluminum foil is determined. Can be evaluated. For the measurement of volume resistivity, “Lorestar EP” (low resistivity meter, Mitsubishi Chemical) was used. The measurement temperature is 20 ° C. The results are shown in Table 1. The perforated metal laminates of Examples 1 to 4 also exhibited conductivity comparable to the perforated copper foil of Comparative Example 3.

(weight)
Perforated metal laminate of Example 1 (thickness 14 μm) that can be used as a negative electrode current collector in a lithium ion capacitor, Perforated metal laminate of Example 2 (thickness 18 μm), and Perforated of Example 3 The weights of the metal laminate (thickness 14 μm), the perforated metal laminate of Example 4 (thickness 18 μm), and the perforated conductive foil of Comparative Example 3 (perforated copper foil (thickness 14 μm)) were compared. . Specifically, assuming that the weight per unit area of the perforated copper foil (thickness 14 μm) of Comparative Example 3 is 100, the perforated metal laminate (thickness 14 μm) of Example 1 and the perforated metal laminate of Example 2 The weight per unit volume of the perforated metal laminate of Example 3 (thickness 14 μm) and the perforated metal laminate of Example 4 (thickness 18 μm) was evaluated. The results are shown in Table 1. The perforated metal laminate (thickness 14 μm) of Examples 1 and 3 having the same thickness as the perforated copper foil (thickness 14 μm) of Comparative Example 3 is lighter than the perforated copper foil (thickness 14 μm) of Comparative Example 3. Of course, the perforated metal laminates (thickness 18 μm) of Examples 2 and 4 which are thicker than the perforated copper foil (thickness 14 μm) of Comparative Example 3 are also lighter than the perforated copper foil (thickness 14 μm) of Comparative Example 3. It is.

Incidentally, the weight per unit volume is 8920 kg / m ³ for Cu and 2700 kg / m ³ for aluminum.

(cost)
Perforated metal laminate of Example 1 (thickness 14 μm) that can be used as a negative electrode current collector in a lithium ion capacitor, Perforated metal laminate of Example 2 (thickness 18 μm), and Perforated of Example 3 Costs were compared for three types of perforated conductive foils, a metal laminate (thickness 14 μm), a perforated metal laminate of Example 4 (thickness 18 μm), and a perforated copper foil of Comparative Example 3 (thickness 14 μm). . Specifically, with the total production cost of the perforated copper foil (thickness 14 μm) of Comparative Example 3 being 100, the perforated metal laminate of Example 1 (thickness 14 μm) and the perforated metal laminate of Example 2 (thickness) 18 μm), the total manufacturing cost of the perforated metal laminate of Example 3 (thickness 14 μm) and the perforated metal laminate of Example 4 (thickness 18 μm) were evaluated. The results are shown in Table 1. Table 2 shows a breakdown of costs. In the perforated metal laminates of Examples 1 to 4, the surface of the perforated aluminum foil requires extra electrical Cu plating, but the difference in material cost is still large even when the cost is taken into consideration. It is cheaper than the perforated copper foil of Example 3.

As a negative electrode current collector in a lithium ion capacitor having a wound laminated structure, a total thickness of 15 μm and a thickness of a perforated aluminum foil of 10 μm are formed on both sides in place of a perforated copper foil having a thickness of 15 μm and an aperture ratio of 50% A laminated perforated conductive foil having a total thickness of 5 μm and an aperture ratio of 50% (the manufacturing method is the same as in Examples 3 and 4) was used. There were no performance issues. The specifications of the lithium ion capacitor here are as follows. Voltage: upper limit is 3.8V, lower limit is 2.2V, capacity: 2200F, internal resistance: 1.4mΩ, weight energy density: 14Wh / L, volume energy density: 25Wh / L, size of each electrode: 0.6m width × 3.3 m long, total area: about 2 m ² .

Also, the original lithium ion capacitor, that is, a lithium ion capacitor that uses a perforated copper foil as a negative electrode current collector, and an improved lithium ion capacitor, that is, a lithium ion that uses a laminated perforated conductive foil as a negative electrode current collector Tables 3 and 4 show the weight per 1 m ² of each constituent material of the capacitor. By using a laminated perforated conductive foil as the negative electrode current collector, the weight of the lithium ion capacitor is reduced by about 5%.

  If the perforated conductive foil of the present invention is used as a negative electrode current collector in a lithium ion capacitor, the weight is maintained while maintaining the same negative electrode capacity as compared with the case where an existing perforated copper foil is used as a negative electrode current collector. In addition, the cost can be reduced.

DESCRIPTION OF SYMBOLS 10 Positive electrode of lithium ion capacitor 11 Current collector 12 Positive electrode active material 20 Negative electrode of lithium ion capacitor 21 Current collector 22 Negative electrode active material 30 Separator 40 Lithium supply source 50 Aluminum foil 51 Perforated aluminum foil 60 Dissimilar metal film 61 Substitution layer 62 Resistance layer 63 Electric Cu plating layer 70 Copper foil 71 Perforated copper foil

Claims (8)

  One or both surfaces of a perforated aluminum foil formed by dispersing a plurality of through-holes are covered with one or more layers of different metal films made of a material different from the aluminum foil, and the outermost layer metal in the different metal film A perforated conductive foil whose layer is made of Cu.   2. The perforated conductive foil according to claim 1, wherein the perforated aluminum foil is a chemical etching product or an electrolytic etching product of aluminum foil.   3. The perforated conductive foil according to claim 1, wherein the dissimilar metal film has a three-layer structure in which a substitution layer made of Zn or a Zn alloy, a resistance layer made of Ni or a Ni alloy, and a Cu layer are laminated in order from the inside. A perforated conductive foil.   4. The perforated conductive foil according to claim 3, wherein the resistance layer is an electroless plating layer of Ni or Ni alloy, and the Cu layer is an electroplating layer.   The perforated conductive foil according to any one of claims 1 to 4, wherein the use of the perforated conductive foil is a negative electrode current collector in a lithium ion capacitor.   A step of dispersing and forming a plurality of through holes in an aluminum foil, a step of replacing the surface of the perforated aluminum foil with Zn or a Zn alloy, and electroless plating of Ni or a Ni alloy on a Zn or Zn alloy replacement film A method for producing a perforated conductive foil, comprising: a step of performing electroplating of Cu on a Ni or Ni alloy plating film.   The method for manufacturing a perforated conductive foil according to claim 6, wherein the formation of the through hole in the aluminum foil is performed by etching.   8. The method for manufacturing a perforated conductive foil according to claim 7, wherein the etching is chemical etching or electrolytic etching.