HK1242044B - Electrode foil, current collector, electrode, and energy storage element using same - Google Patents

Description

Electrode foil, current collector, electrode, and storage device using the same

This application is a divisional application, the application number of the parent application is 201280009644.6, the application date is February 20, 2012, and the name of the invention is "Electrode foil, collector, electrode and storage component using the same".

Technical Field

The present invention relates to solid electrolytic capacitors having a solid electrolyte layer (typically a conductive polymer layer) formed therein, and electrode foils that can be used in such capacitors. Furthermore, the present invention relates to current collectors and electrodes, as well as storage devices such as batteries, electric double-layer capacitors, and hybrid capacitors that utilize these.

Background Art

Prior art related to solid electrolytic capacitors

In recent years, as the operating frequencies of electronic devices have increased, electrolytic capacitors, one of the electronic components, have become increasingly demanding, exhibiting superior impedance characteristics in higher operating frequency ranges than before. In response to this demand, various solid electrolytic capacitors have been developed, using highly conductive polymers as solid electrolytes. These solid electrolytic capacitors offer excellent high-frequency characteristics in addition to longevity and temperature resistance, leading to their widespread adoption in applications such as personal computer circuits.

As one of the simplest examples, a wound solid electrolytic capacitor can be made using the following steps:

(i) After chemically treating the surface of the anode aluminum foil to form an oxide film, the anode aluminum foil and the cathode aluminum foil are overlapped with each other through a separator paper, and a lead material is connected to each electrode foil and then wound to produce a capacitor component;

(ii) The fabricated capacitor assembly is placed in an aluminum case, immersed in a conductive polymer solution, and heated to thermally polymerize the conductive polymer, thereby forming a solid conductive polymer layer between the two electrode foils.

If the anode aluminum foil is used as the anode and the cathode aluminum foil and the conductive polymer layer electrically connected to the cathode aluminum foil are used as the cathode, since these two electrodes are connected through the insulating oxide film, charging and discharging can be performed between the two electrodes.

In the above-mentioned solid electrolytic capacitor, the cathode aluminum foil is not subjected to a chemical conversion treatment, so there is no artificially formed oxide film. However, due to natural oxidation during actual manufacturing and use, an oxide film also forms on the cathode aluminum foil. In this case, the entire solid electrolytic capacitor has a layered structure consisting of (i) anode aluminum foil, (ii) oxide film on the anode aluminum foil, (iii) conductive polymer layer, (iv) natural oxide film on the cathode aluminum foil, and (v) cathode aluminum foil, forming a state equivalent to two capacitors connected in series, resulting in a problem of reduced electrostatic capacitance of the solid electrolytic capacitor as a whole.

To address this problem, research has been conducted to prevent the generation of electrostatic capacitance components in the cathode to increase the electrostatic capacitance of the capacitor. Several cathode foils obtained from previous research and the problems associated with these conventional cathode foils are described below.

Patent Documents 1 and 2 disclose cathode foils that form a chemical coating on the surface of a cathode aluminum foil, and then deposit a coating of a metal nitride such as TiN or a metal carbide such as TiC on top of the coating by vapor deposition. However, metals such as Ti and their nitrides and carbides have insufficient thermal oxidation resistance. Therefore, the heat treatment involved in capacitor manufacturing on this type of cathode foil causes the oxide coating to grow, generating an electrostatic capacitance component and increasing ESR (equivalent series resistance).

Patent Document 3 discloses a cathode foil having a carbon coating formed on the surface of a valve metal. However, when carbon is directly deposited on a metal foil such as aluminum, the adhesion between the metal foil and the carbon coating is poor, leading to an increase in ESR.

Patent Document 4 discloses a cathode foil having a carbon- _containing layer formed on the surface of an aluminum foil. An intervening layer composed of fibrous or filamentous aluminum carbide ( _Al4C3 , aluminum carbide filaments) is formed between the aluminum foil surface and the carbon-containing layer to improve interlayer adhesion. However, in this type of cathode foil, the carbon-containing layer is composed of carbon particles, and the contact between the aluminum foil surface and the carbon-containing layer is point contact. This leads to an increase in interfacial resistance due to the small contact area. Furthermore, the carbon-containing layer is formed by coating the aluminum foil surface with a carbon-containing substance and then subjecting the carbon particles to a heat-drying treatment. This makes it difficult to form a thinner carbon-containing layer, which increases the electron conduction distance between the aluminum layer and the solid electrolyte layer, leading to an increase in ESR. Furthermore, this type of cathode foil lacks water resistance. In particular, in high-temperature environments, the aluminum carbide filaments, which serve as the electron conduction path, can be severed, resulting in reduced conductivity.

Patent Document 5 discloses a cathode foil formed by vacuum-depositing a Ni film on a roughened aluminum foil. According to Patent Document 5, the Ni oxide film formed on the surface of the Ni layer is both semiconducting and conductive, thus contributing to a lower ESR capacitor. However, the reduction in conductivity caused by the oxide film cannot be ignored, and semiconductors are still insufficient as a film-forming material. It is still preferable to use a conductive material with good oxidation resistance, at least for the topmost layer of the film.

In addition, for cathode foil used in electrolytic capacitors that operate with a driving electrolyte instead of solid-state electrolysis, Patent Document 6 discloses a cathode foil in which a metal such as Ti is vapor-deposited on a roughened aluminum foil to form a metal coating, and then the carbon particles are fixed by applying an adhesive dispersed with carbon particles and subsequently heat-treating the coating. However, in the cathode foil described in Patent Document 6, the surface of the Ti coating is oxidized by the driving electrolyte, resulting in a large resistance at the interface between the layer composed of the Ti coating and the layer composed of carbon, which increases the ESR of the capacitor (in the cathode foil described in Patent Document 6, in order to suppress the effects of such Ti oxidation, it is preferably subjected to a roughening treatment such as etching). In addition, when used as a solid electrolytic capacitor, the heat treatment included in the capacitor manufacturing step causes the oxide coating to grow, thereby increasing the ESR. In addition, even if the Ti coating and carbon are bonded by an adhesive, a large interface resistance is generated at the bonded portion, which increases the ESR of the capacitor.

In solid electrolytic capacitors, moderately roughening the cathode foil surface generally increases the contact area with the solid electrolyte layer, thereby reducing ESR, but this effect is minimal. Furthermore, when the aluminum substrate surface is roughened by etching or other processes, spaces are formed between the film and the aluminum substrate within the resulting micropores. Chemicals and water used in the capacitor manufacturing process react in these spaces, causing the surface to become unstable. Furthermore, oxygen diffusion makes the interface between the aluminum substrate and the film susceptible to oxidation, leading to increased interfacial resistance and capacitor degradation. Furthermore, as the surface roughening progresses, there is also the problem of increased capacitor manufacturing costs.

As mentioned above, conventional cathode foils, which first form a metal film on aluminum foil, have the problem of oxidation on the film surface. If the oxidation reaction progresses over time, the cathode will have electrostatic capacitance. Furthermore, conventional cathode foils, which form a carbon layer directly on the aluminum foil or with a metal film interposed therebetween, can also have electrostatic capacitance if the interlayer adhesion is insufficient. This reduces the overall electrostatic capacitance of the solid electrolytic capacitor, as already explained. Furthermore, each of these conventional cathode foil systems has the problems of increased ESR and increased costs.

Prior art related to batteries, electric double layer capacitors, hybrid capacitors, etc.

In recent years, the demand for power storage devices used in portable electronic devices has been increasing due to the increasing multifunctionality of portable electronic devices, improvements in fuel costs for automobiles, transportation, and construction vehicles, the widespread use of distributed renewable energy, and the expansion of emergency backup power sources. Examples of power storage devices include electric double-layer capacitors, hybrid capacitors, and batteries, and these devices are required to achieve further improvements in output density (W/kg, W/L) and lifespan characteristics.

The electrodes that make up these storage components often use current collectors made of metal foil, from the perspectives of performance such as processing strength and electrical conductivity, as well as productivity and manufacturing costs. The electrodes are formed on a current collector with an electrode layer composed of an active material, a conductive auxiliary agent, and a binder. However, if the adhesion between the current collector and the electrode layer, as well as the electrical conductivity and chemical stability, are insufficient, the output density cannot be achieved due to the increase in contact resistance, making rapid charging and discharging difficult. Furthermore, as the storage component undergoes charge and discharge cycles, the interface between the current collector and the electrode layer deteriorates over time due to chemical changes such as oxidation, or the electrode layer peels off from the current collector, which may increase internal resistance or reduce lifespan.

In this regard, for example, Patent Document 7 discloses a battery in which a carbon coating layer is formed between a current collector and an active material.

However, when a carbon layer is formed directly on a metal foil, the adhesion, electrical conductivity, and chemical stability between the metal foil and the carbon coating layer are insufficient. This gradually increases the contact resistance between the current collector and the electrode layer, eventually leading to a decrease in output density and an increase in internal resistance, making rapid charging and discharging difficult. The inventors' research has revealed related prior art documents, including Patent Documents 8 to 11, but the coating structures disclosed in these documents also suffer from similar issues.

Prior Art Literature

Patent Literature

Patent Document 1: Japanese Patent Application Laid-Open No. 2007-36282

Patent Document 2: Japanese Patent Application Laid-Open No. 2007-19542

Patent Document 3: Japanese Patent Application Laid-Open No. 2006-190878

Patent Document 4: Japanese Patent Application Laid-Open No. 2006-100478

Patent Document 5: Japanese Patent Application Laid-Open No. 2009-49376

Patent Document 6: Japanese Patent Application Laid-Open No. 2007-95865

Patent Document 7: Japanese Patent Application Laid-Open No. 11-250900

Patent Document 8: Japanese Patent Application Laid-Open No. 2011-142100

Patent Document 9: Japanese Patent Application Laid-Open No. 2010-218971

Patent Document 10: Japanese Patent Application Laid-Open No. 2009-283275

Patent Document 11: Japanese Patent Application Laid-Open No. 2008-270092

Summary of the Invention

Problems to be solved by the invention

The present invention was created to address the aforementioned problems in the prior art. Specifically, the present invention aims to prevent the generation of electrostatic capacitance in the cathode by improving the oxidation resistance of the layers comprising the coating and the interlayer adhesion in a cathode foil for a solid electrolytic capacitor formed by forming a coating on aluminum foil. Another object of the present invention is to prevent the generation of high interfacial resistance due to abrupt changes in the coating composition in such cathode foil, thereby reducing the capacitor's ESR and leakage current (LC).

Furthermore, the purpose of the present invention is to solve the problems in the prior art disclosed in patent documents 7 to 11, and to achieve a storage component that can reduce the increase in internal resistance for a long period of time, maintain a high output density for rapid charging and discharging, and has excellent life characteristics, thereby improving the adhesion and electrical conductivity between the collector and the electrode layer, and suppressing deterioration caused by chemical changes at the interface between the collector and the electrode layer.

Means to solve problems

In order to solve the above-mentioned problems, the present invention provides an electrode material, characterized in that a first conductive layer, a mixed layer formed by a mixture of a substance constituting the first conductive layer and carbon, and a second conductive layer substantially composed of carbon are formed on an electrode substrate; the composition of the mixed layer is as follows: from the first conductive layer toward the second conductive layer, the composition changes from a composition substantially containing only the substance constituting the first conductive layer to a composition substantially containing only carbon.

In the electrode material provided by the present invention, owing to be formed with the mixed existence layer of the constituent components of two conductive layers between the first conductive layer and the second conductive layer, the adhesion between the material constituting the first conductive layer and carbon can be improved. According to this formation, the problem of the prior art that the electrode material has electrostatic capacitance and ESR also rises due to insufficient adhesion between carbon and the material constituting the first conductive layer can be solved. In addition, the second conductive layer is substantially composed of carbon, so it has good oxidation resistance. Moreover, in the boundary region with the first conductive layer, the mixed existence layer substantially only contains the material constituting the first conductive layer, and in the boundary region with the second conductive layer, the mixed existence layer substantially only contains carbon, so it also can not cause the problem of producing larger interface resistance in these boundary regions due to the rapid change of the composition of the electrode material.

The phrase "substantially contains only the substance constituting the first conductive layer" in the above description does not necessarily mean that it is completely free of components other than the substance constituting the first conductive layer. The actual composition of the components at the interface between the mixed layer and the conductive layers may vary depending on factors such as the control of the purity of the components within the layer, manufacturing technology limitations related to impurity incorporation, and the tolerance for capacitance variation in the electrode material in individual products. This also applies to phrases such as "substantially composed of carbon" and "substantially containing only carbon."

Furthermore, the statement above that "the composition of the mixed layer changes from a composition consisting essentially solely of the substance constituting the first conductive layer toward the second conductive layer to a composition consisting essentially solely of carbon" does not necessarily mean that the carbon content within the mixed layer increases monotonically from the first conductive layer toward the second conductive layer. The actual composition at each location within the mixed layer may vary due to variations in the concentrations of the various components caused by limitations in manufacturing technology. However, it is preferred that the mixed layer be formed so that the carbon content increases continuously from the first conductive layer toward the second conductive layer.

The first conductive layer may contain any of Ta, Ti, Cr, Al, Nb, V, W, Hf, Cu, nitrides of these metals, and carbides of these metals. The materials that can be used to form the first conductive layer of the electrode material of the present invention are not limited thereto. However, when an aluminum substrate is used as the electrode substrate, the materials listed above are preferably used from the perspective of energy efficiency and adhesion to the aluminum substrate. Metals such as Ti and Al are most preferably used (alloys containing multiple components are also possible, as long as adhesion to the substrate or the conductivity of the first conductive layer is not impaired). The material that can be used as the electrode substrate is not limited to aluminum. Any other valve-acting metal such as Ta, Ti, or Nb, or aluminum alloys containing these materials added to aluminum, may also be used.

Roughening the electrode substrate is not a necessary condition for the electrode material of the present invention. As demonstrated by the performance test data in the examples below, even when the electrode substrate is not roughened, solid electrolytic capacitors using the electrode material of the present invention exhibit superior capacitance, ESR, and leakage current characteristics compared to conventional solid electrolytic capacitors. In particular, electrode substrates of the present invention produced without roughening exhibit superior heat resistance compared to those with roughening, as will be demonstrated in the examples below.

In addition, the present invention provides a solid electrolytic capacitor, which includes a capacitor assembly having: an anode foil and a cathode foil; a separator arranged between the anode foil and the cathode foil; and a solid electrolyte layer formed between the anode foil and the cathode foil; the solid electrolytic capacitor is characterized in that the above-mentioned electrode material is used as the aforementioned cathode foil.

The electrode material of the present invention is particularly suitable for use as cathode foil in wound or laminated solid electrolytic capacitors, but can also be used in various capacitors including electrolytic capacitors that operate using an electrolyte, as well as electric double layer capacitors, lithium ion capacitors, lithium ion batteries, solar cells, etc.

Specifically, if a layer composed of activated carbon is formed on the above-mentioned second conductive layer of the electrode material of the present invention, which is essentially composed of carbon, the electrode material can be used as a positive electrode or negative electrode for an electric double-layer capacitor (an electrode material of this type can also be directly used as a positive electrode of a lithium-ion capacitor). Alternatively, if a layer composed of an active material containing Li is formed on the above-mentioned second conductive layer of the electrode material of the present invention, the electrode material can be used as a positive electrode of a lithium-ion battery.

That is, the electrode material of the present invention can not only be used as an electrode directly in this state, but can also be used as an anode (positive electrode) or cathode (negative electrode) in any power storage device by forming additional layers as described above and performing further processing as needed.

The solid electrolyte layer can contain any of manganese dioxide ( _MnO2 ), tetracyanoquinodimethane (TCNQ), polyethylenedioxythiophene (PEDOT), polyaniline (PANI), and polypyrrole, but electrolytes other than these can also be used. For example, a solid electrolyte layer composed of PEDOT can be formed by immersing the capacitor element in a mixed solution of 3,4-ethylenedioxythiophene and iron (II) p-toluenesulfonate and heating it to thermally polymerize the electrolyte.

Regarding a typical embodiment of the aforementioned electrode material, the present invention provides a cathode foil for use in a solid electrolytic capacitor comprising a capacitor assembly, the capacitor assembly comprising: an anode foil and a cathode foil; a separator disposed between the anode and cathode foils; and a solid conductive polymer layer formed between the anode and cathode foils. The cathode foil is characterized by comprising: an unroughened aluminum foil; a metal layer formed on the aluminum foil and consisting essentially of titanium or aluminum; a mixed layer formed on the metal layer and consisting of a mixture of titanium or aluminum and carbon; and a carbon layer formed on the mixed layer and consisting essentially of carbon; the composition of the mixed layer changing from a composition consisting essentially solely of titanium or aluminum to a composition consisting essentially solely of carbon as one moves toward the carbon layer.

The cathode foil corresponds to a typical embodiment of the present invention as described in the following examples using performance test data. However, the embodiment for solving the above-mentioned problems of the prior art is obviously not limited thereto.

For example, from the performance tests described later, it can be seen that in the cathode foil of the present invention, even if the aluminum substrate is roughened, the solid electrolytic capacitor using this has excellent electrostatic capacitance and other properties compared to the past, and the material that can be used as the electrode material is not limited to aluminum. From the perspective of adhesion to aluminum, the material used for the metal layer is preferably either Ti or Al, but other materials with excellent adhesion to aluminum such as Ta and Cr can also be used. Or when other electrode substrates are used, the metal layer can be formed using appropriate materials according to the substrate. For example, when copper foil is used as the electrode substrate, if a metal layer composed of Cr with good adhesion to the copper foil is formed by ion evaporation, it can be inferred that the Cr penetrates the natural oxide film on the surface of the copper foil and directly combines with the copper foil to obtain high electrical conductivity and suppress the generation of electrostatic capacitance components. Therefore, the same properties as when a metal layer composed of Ti or Al is formed on the aluminum foil can be obtained.

Furthermore, in the cathode foil of the present invention, a mixed layer containing a mixture of the components that make up each layer is formed between the metal layer and the carbon layer. The improved adhesion between the metal and carbon achieved by the introduction of this mixed layer is evident even when the metal layer is formed of materials other than Ti or Al. It is speculated that this improved adhesion prevents the formation of an oxide film on the metal, thereby suppressing the generation of electrostatic capacitance in the cathode foil. Furthermore, the mixed layer contains essentially only Ti or Al in the interface region with the metal layer, and essentially only carbon in the interface region with the carbon layer. Therefore, the interface resistance can be suppressed to a low level without causing a sudden change in composition in these interface regions. This effect is evident even when the metal layer is formed of materials other than Ti or Al.

In order to solve the problems in the prior art disclosed in Patent Documents 7 to 11, the present invention provides an electrode collector, characterized in that: a first conductive layer containing metal is formed on a metal-containing substrate; a mixed layer is formed by a mixture of a substance constituting the first conductive layer containing metal and carbon; and a second conductive layer substantially composed of carbon; the composition of the aforementioned mixed layer is as follows: from the aforementioned first conductive layer containing metal toward the aforementioned second conductive layer, the composition changes from substantially only containing the substance constituting the aforementioned first conductive layer containing metal to substantially only containing carbon.

In the current collector provided by the present invention, since a first conductive layer containing metal and a mixed layer containing a mixture of the constituent components of the two conductive layers are formed between the surface of the metal-containing substrate and the second conductive layer substantially composed of carbon, the adhesion between the substrate and the first conductive layer and the adhesion between the first conductive layer and the second conductive layer can be improved, thereby improving the electrical conductivity and chemical stability of each interface. According to this structure, the problem of the prior art that the contact resistance between the current collector and the electrode layer increases due to insufficient adhesion between the substrate and carbon and insufficient electrical conductivity or chemical stability of the interface, and the internal resistance of the current collector increases with repeated use, thereby reducing the output density of the electrode, can be solved. In addition, since the second conductive layer is substantially composed of carbon, it has excellent electrical conductivity and resistance to chemical changes such as oxidation. Furthermore, in the boundary region between the first conductive layer and the second conductive layer, the region on the first conductive layer side within the mixed layer substantially only contains the substance constituting the first conductive layer, and the region on the second conductive layer side within the mixed layer substantially only contains carbon. Therefore, there will be no problem of generating a large interface resistance due to a rapid change in composition in these boundary regions.

The phrase "substantially contains only the substance constituting the metal-containing first conductive layer" does not necessarily mean that it is completely free of components other than the substance constituting the first conductive layer. The actual composition of the components at the interface between the mixed layer and the conductive layers may vary depending on factors such as the control of the purity of the components within the layer, manufacturing technology limitations related to impurity incorporation, and the degree of adhesion or contact resistance that can be tolerated in individual products as a factor in the current collector. This also applies to phrases such as "substantially composed of carbon" and "substantially containing only carbon."

Furthermore, the statement above that "the composition of the mixed layer changes from a composition consisting essentially solely of the substance constituting the first conductive layer containing metal toward the second conductive layer to a composition consisting essentially solely of carbon" does not necessarily mean that the carbon content within the mixed layer increases monotonically from the first conductive layer toward the second conductive layer. The actual composition at each location within the mixed layer may vary due to variations in the concentrations of the various components caused by limitations in manufacturing technology. However, it is preferred that the mixed layer be formed so that the carbon content increases continuously from the first conductive layer toward the second conductive layer.

The first conductive layer may contain any of Ta, Ti, Cr, Al, Nb, V, W, Hf, Cu, nitrides of these metals, and carbides of these metals. The materials that can be used to form the first conductive layer of the current collector of the present invention are not limited to these. However, when aluminum foil is used as the metal-containing substrate, the materials listed above are preferred from the perspectives of energy efficiency and adhesion to the aluminum foil. Metals such as Ti and Al are more preferred (alloys containing multiple components, etc., may also be used as long as adhesion to the substrate or the electrical conductivity of the first conductive layer is not impaired).

The carbon used in the second conductive layer is not particularly limited. Among carbon materials, graphite-like carbon, which has particularly good electrical conductivity, is more ideal because it can increase the output density of the storage component. In addition, it is also preferable from the perspective of manufacturing cost. Here, the so-called graphite-like carbon refers to carbon with an amorphous structure in which diamond bonds ( ^sp3 hybrid orbital bonds of carbon) and graphite bonds ( ^sp2 hybrid orbital bonds of carbon) are mixed, and the ratio of graphite bonds is more than half. However, in addition to the amorphous structure, it also includes a phase having a crystalline structure partially composed of a graphite structure (i.e., a hexagonal crystalline structure composed of ^sp2 hybrid orbital bonds).

The material that can be used as the metal-containing substrate is not limited to aluminum. Any other material, such as Ti, Cu, Ni, Hf, or stainless steel, or metal foil composed of aluminum alloys containing these materials can also be used. The metal foil used as the current collector in the positive and negative electrodes of each storage component can be selected based on electrochemical stability, electrical conductivity, weight, processability, and manufacturing costs, taking into account the action potentials of the electrolyte and active material. When the storage component is an electric double-layer capacitor, it is preferred that both the positive and negative electrodes be aluminum foil. When the storage component is a hybrid capacitor or battery, it is preferred that the positive electrode be aluminum foil and the negative electrode be aluminum foil or copper foil.

In the current collector of the present invention, it is not a necessary condition to roughen the surface of the metal-containing substrate. However, as described in the performance test data in the examples described later, when making the current collector of the present invention, the roughened substrate can improve the adhesion between the current collector and the electrode layer or the current collecting capacity, so it is more beneficial for improving the output density or life characteristics. In addition to the effects described so far in relation to the first conductive layer, the mixed layer, and the second conductive layer containing metal, it is also possible to achieve an improvement in the adhesion strength between the current collector and the electrode layer due to the physical anchoring effect, and a reduction in the contact resistance due to the increase in the contact area between the two. In particular, in hybrid capacitors or batteries where the active material repeatedly expands and contracts in volume due to the absorption (intercalation) and release (deintercalation) of ions, roughening the substrate is more effective. While there are no particular limitations on the method for roughening the surface, when aluminum foil or copper foil is used as the substrate material as described above, roughening is preferably performed by chemical or electrochemical etching using an acid or alkaline solution. This method can easily achieve a fine pore structure that helps improve adhesion to the electrode layer due to the anchoring effect, and is also a method with good productivity. In hybrid capacitors such as lithium-ion capacitors or batteries such as lithium-ion batteries, when it is necessary to pre-dope the active material of the positive electrode and/or negative electrode within the component so that alkali metal ions or alkaline earth metal ions are generally absorbed, through holes can also be formed in the metal foil in advance, depending on the form of the manufacturing method or production conditions.

The total thickness of the first conductive layer, the second conductive layer, and the mixed layer is not particularly limited. For example, if this thickness is set to 45 nm or less, the electron conduction distance between the current collector and the electrode layer can be prevented from increasing, further enhancing the internal resistance reduction effect. In particular, when the metal foil is roughened as described above, if a current collector with such a small total thickness is produced, the fine and compact pore structure formed in the metal foil by etching, etc., will not be buried by the coating formed above it, and the anchoring effect and contact area increase effect described above will not be impaired. Furthermore, it is unnecessary to form the first and second conductive layers everywhere on the inner walls of the pore structure. When the current collector is used on the negative electrode side of a hybrid capacitor or battery, the carbon constituting the second conductive layer itself can become an active material capable of occluding and releasing either alkali metal ions or alkaline earth metal ions. However, in order to achieve sufficient energy density (Wh/kg, Wh/L) as a storage battery, the electrode layer containing the active material is required to have a thickness of at least 1 μm. However, from the perspective of productivity and manufacturing cost, forming the second conductive layer to a thickness of approximately 1 μm, which is sufficient for use as an active material, is not effective. It is preferable to form the electrode layer containing the active material as a separate layer from the second conductive layer constituting the current collector of the present invention.

The present invention provides an electrode and a battery using the electrode as a positive electrode and a negative electrode. The battery is, for example, a lithium ion battery, a sodium ion battery, a magnesium ion battery, a calcium ion battery, or the like. The battery comprises: a positive electrode forming an electrode layer, the electrode layer being composed of an active material comprising a transition metal oxide or a transition metal phosphate compound containing either an alkali metal or an alkaline earth metal, a conductive auxiliary agent, and a binder; and a negative electrode forming an electrode layer, the electrode layer being composed of a carbon material capable of absorbing or releasing either an alkali metal ion or an alkaline earth metal ion, and containing an active material comprising either Sn, Si or silicon oxide, S or sulfide, or titanium oxide, a conductive auxiliary agent, and a binder. The battery is characterized by using the above-mentioned current collector. Here, a transition metal oxide or transition metal phosphate containing either an alkali metal or an alkaline earth metal contained in the positive electrode active material in the above-mentioned storage battery is used, and examples thereof include _LiCoO2 , _LiMn2O4 , _LiNiO2 , Li( _Ni -Mn-Co) _O2 , Li(Ni-Co- _Al ) _O2 , _LiFePO4 , _NaCrO2 , _NaFeO2 , MgHf( _MoO4 ) ₃ , _Ca3Co2O6 , _{and Ca3CoMnO6 .}

The present invention provides an electrode and an electric double-layer capacitor using the electrode as a positive electrode and a negative electrode. The electric double-layer capacitor uses: a positive electrode forming an electrode layer, wherein the electrode layer is composed of an active material containing either activated carbon or carbon nanotubes, a conductive auxiliary agent, and a binder; and a negative electrode forming the same layer structure. The electric double-layer capacitor is characterized by using the above-mentioned collector.

In addition, the present invention provides an electrode and a hybrid capacitor using the electrode as a positive electrode and a negative electrode. The hybrid capacitor is, for example, a hybrid capacitor such as a lithium ion capacitor, which has: a positive electrode forming an electrode layer, the electrode layer being composed of an active material containing any one of activated carbon and carbon nanotubes, a conductive auxiliary agent, and a binder; and a negative electrode forming an electrode layer, the electrode layer being composed of a carbon material that can absorb or release any one of alkali metal ions and alkaline earth metal ions, and containing an active material of any one of Sn, Si or silicon oxide, S or sulfide, and titanium oxide, a conductive auxiliary agent, and a binder. The hybrid capacitor is characterized by the use of the above-mentioned collector.

Effects of the Invention

In the electrode material of the present invention, the interlayer adhesion is improved by forming a mixed layer between the first and second conductive layers formed on the electrode substrate, thereby preventing oxidation of the material constituting the first conductive layer. Furthermore, in the interface region between the first or second conductive layer and the mixed layer, the mixed layer is essentially composed solely of the components constituting the first or second conductive layer. This prevents an increase in interfacial resistance caused by a sudden change in the composition of the electrode material in the interface region. By using this type of electrode material as cathode foil, it is possible to achieve an increase in capacitance and a reduction in ESR and leakage current in solid electrolytic capacitors.

In addition, as shown in the performance test data described later, the electrode material of the present invention has excellent heat resistance and its quality hardly deteriorates even when used for a long time at high temperatures. In addition, even if the coating on the aluminum substrate composed of the first conductive layer, the mixed layer, and the second conductive layer is thinned to about 0.02 μm, the characteristics of the electrode material of the present invention as a cathode foil will hardly be reduced. In addition, it is not necessary to roughen the surface of the electrode substrate when making the cathode foil, so the materials used can be reduced and the manufacturing steps can be simplified, thereby significantly reducing manufacturing costs. If the coating is formed thinner, the risk of cracking when winding the cathode foil is also reduced. Furthermore, if the coating is formed thinner, the electron conduction distance between the electrode substrate and the solid electrolyte layer can be shortened, further reducing ESR.

In the current collector of the present invention, the interlayer adhesion, electrical conductivity, and chemical stability are improved by forming a mixed layer between the first and second conductive layers formed on the substrate, thereby preventing deterioration caused by chemical changes such as oxidation of the substrate surface and the material constituting the first conductive layer. In addition, in the boundary area between the first or second conductive layer and the mixed layer, the mixed layer is essentially composed only of the components constituting the first or second conductive layer, thereby preventing an increase in interface resistance due to a rapid change in the composition of the electrode material in the boundary area. The positive electrode or negative electrode having an electrode layer composed of an active material, a conductive auxiliary agent, and a binder formed on this type of current collector has good electrical conductivity and a good ability to collect electricity from the electrode layer to the current collector, and also has good chemical stability, so the high adhesion between the current collector and the electrode layer can be maintained for a long time. In storage components such as batteries, electric double-layer capacitors, and hybrid capacitors that use these electrodes, output density is improved and voltage drop during charge and discharge is reduced. This can suppress the rise in component temperature during charge and discharge with large currents, allowing continuous charge and discharge for long periods of time, significantly extending the charge and discharge cycle life.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a cross-sectional view showing the layer structure of a cathode foil according to one embodiment of the present invention.

FIG. 2 is an exploded view showing the structure of a wound solid electrolytic capacitor according to an embodiment of the present invention.

FIG. 3 is a bar graph comparing the electrostatic capacitances measured for a solid electrolytic capacitor using the cathode foil according to an embodiment of the present invention and a solid electrolytic capacitor using a conventional cathode foil.

FIG. 4 is a bar graph comparing ESR values measured for a solid electrolytic capacitor using the cathode foil according to an embodiment of the present invention and a solid electrolytic capacitor using a conventional cathode foil.

FIG. 5 is a bar graph comparing leakage currents measured for a solid electrolytic capacitor using the cathode foil according to an embodiment of the present invention and a solid electrolytic capacitor using a conventional cathode foil.

6 is a bar graph comparing capacitance change rates before and after a heat resistance test of a solid electrolytic capacitor using the cathode foil according to an embodiment of the present invention and a solid electrolytic capacitor using a conventional cathode foil.

7 is a bar graph comparing ESR change rates before and after a heat resistance test of a solid electrolytic capacitor using the cathode foil according to an embodiment of the present invention and a solid electrolytic capacitor using a conventional cathode foil.

FIG8 is a cross-sectional view showing the layer structure of a current collector according to one embodiment of the present invention.

FIG9 is a cross-sectional view showing the layer structure of a positive electrode or a negative electrode according to one embodiment of the present invention.

FIG10 a is an exploded view showing the structure of a lithium ion secondary battery according to an embodiment of the present invention.

FIG. 10 b is a diagram showing the external appearance structure of a lithium ion secondary battery according to an embodiment of the present invention.

FIG. 11 shows a comparison of discharge rate characteristics measured for a lithium ion secondary battery using a current collector according to an embodiment of the present invention and a lithium ion secondary battery using a current collector as a comparative example.

FIG. 12 shows a comparison of charge and discharge cycle life characteristics measured for a lithium ion secondary battery using the current collector according to one embodiment of the present invention and a lithium ion secondary battery using a current collector as a comparative example.

13 shows the results of a SAICAS test comparing the adhesion strength between the current collector and the electrode layer of a positive electrode for a lithium ion secondary battery using the current collector according to an embodiment of the present invention and a positive electrode for a lithium ion secondary battery using a current collector as a comparative example.

【Main component symbol description】

1.8 cathode foil 2 smooth aluminum foil

3 Metal layer 4 Mixed layer

5-carbon layer 6-wound solid electrolytic capacitor

7 Anode foil 9 Separator paper

10 Capacitor assembly 11 Anode terminal

12 cathode terminal 13 aluminum box

14 Sealing rubber 15 Metal foil

16 Metal layer 17 Mixed layer

18 Carbon layer 19 Current collector (19a positive electrode side current collector, 19b negative electrode side current collector)

20 positive electrode layer 21 positive electrode

22 negative electrode layer 23 negative electrode

24 separator 25 electrolyte

26 positive terminal 27 negative terminal

28 Lithium-ion battery pack 29 Battery box

30 lithium-ion batteries

DETAILED DESCRIPTION

(First embodiment)

The following describes a cathode foil comprising a first conductive layer composed of Ti or Al, a mixed layer composed of Ti or Al and carbon, and a second conductive layer composed of carbon, formed on an unroughened aluminum foil, and a solid electrolytic capacitor fabricated using this cathode foil, as one embodiment of the present invention. However, as already explained, the aluminum foil used as the base material and the Ti or Al used to form the first conductive layer can be replaced with other materials. Furthermore, as demonstrated by performance test data, the cathode foil of the present invention exhibits excellent properties even without roughening the base material surface.

(Cathode Foil of the Present Invention)

FIG1 is a cross-sectional view showing the layer structure of cathode foil 1 according to one embodiment described above. Cathode foil 1 comprises: a smooth aluminum foil 2 that has not been roughened by etching or the like; a metal layer 3 composed of Ti or Al formed on smooth aluminum foil 2; a mixed layer 4 composed of a mixture of Ti or Al and carbon formed on metal layer 3; and a carbon layer 5 formed on mixed layer 4.

A commercially available high-purity aluminum foil can be used as the smooth aluminum foil 2. The thickness of the aluminum foil is not particularly limited, but is preferably 20 μm to 50 μm when used as a cathode foil for a wound solid electrolytic capacitor.

After placing a smooth aluminum foil 2 and a metal material such as Ti or Al as an evaporation source in a vacuum reaction chamber, the Ti or Al is evaporated and ionized using an electron beam or plasma-generating electrode. The resulting metal cations are then directed toward the smooth aluminum foil 2 to form the metal layer 3. At this time, a negative bias voltage is applied to the smooth aluminum foil 2, accelerating the metal ions toward the smooth aluminum foil 2 and imparting high energy (ion evaporation). Consequently, the Ti or Al ions penetrate the natural oxide film formed on the surface of the smooth aluminum foil 2, firmly adhering to the smooth aluminum foil 2. In the case of forming a layer composed of a nitride or carbide of a metal such as Ti or Al on the smooth aluminum foil 2, the first conductive layer can be formed by performing the above-described method in an atmosphere such as nitrogen or methane.

In addition to ion evaporation, other methods for forming the metal layer 3 include vacuum evaporation, chemical vapor deposition (CVD), sputtering, and the like. However, ion evaporation is preferred from the perspective of maintaining a low ESR of the capacitor by allowing the metal layer 3 and the smooth aluminum foil 2 to penetrate the natural oxide film and firmly adhere to each other, and from the perspective of facilitating the formation of a smooth metal film.

The mixed layer 4, like the metal layer 3, can be formed by ion deposition or the like. Specifically, a carbon material can be prepared as an evaporation source in addition to the metal material of Ti or Al, and the film formation process can be performed using these two evaporation sources simultaneously. The introduction of this mixed layer 4 improves the adhesion between the metal and carbon, preventing the formation of an oxide film.

The mixed layer 4 is preferably configured to contain substantially only Ti or Al in the boundary region with the metal layer 3 and substantially only carbon in the boundary region with the carbon layer 5, with the carbon content increasing continuously from the metal layer 3 toward the carbon layer 5. An example of such a mixed layer 4 can be formed as follows:

(i) When forming the mixed layer 4, the electron beam is irradiated only on the metal material to form a coating of only Ti or Al;

(ii) gradually reducing the electron beam exposure to the metal material over time while increasing the electron beam exposure to the carbon material, thereby forming a mixed film in which the metal and carbon are mixed and the carbon content increases toward the upper layers;

(iii) When film formation is completed, the electron beam irradiation dose to the metal material is set to zero, thereby forming a carbon coating alone. Alternatively, when forming the mixed layer 4 by sputtering, the mixed layer 4 of a preferred type may be formed by any method, such as decreasing the voltage applied to the metal target (decreasing the sputtering rate of the metal target) or increasing the voltage applied to the C target (increasing the sputtering rate of the C target) over time.

The performance test data described below refers to data from Examples 7 to 12 obtained using the aforementioned ion vapor deposition method, with cathode foil 1 having a mixed layer 4 formed such that the carbon content increases continuously from the metal layer 3 toward the carbon layer 5. However, even if the mixed layer 4 has regions where the carbon content decreases as it moves toward the carbon layer 5 (this may occur due to limitations in film formation technology, etc.), it is speculated that the same cathode foil can achieve better properties than conventional cathode foils. This is because the presence of Ti or Al mixed with carbon in such regions improves the adhesion between the components, thereby preventing oxidation of the Ti or Al and suppressing the generation of internal capacitance in the cathode. Furthermore, if the carbon content in a region of the mixed layer 4 changes discontinuously, the ESR characteristics may be slightly reduced due to the increase in interface resistance in that region. However, due to the improved adhesion between the components caused by the presence of Ti or Al mixed with carbon, it is speculated that the cathode foil can achieve the same properties. (For this point, please refer to the data from Examples 1 to 6 in the performance test data described below.)

The carbon layer 5 can be formed by ion deposition, etc., similarly to the metal layer 3 and the mixed layer 4. Typically, in the process of forming the mixed layer 4, after reducing the electron beam irradiation amount on the metal material to zero, the coating forming process is continued for a certain period of time while irradiating only the carbon material with the electron beam, thereby forming the carbon layer 5.

The carbon layer 5 of the present invention is not formed by dispersing carbon particles in a binder, applying the binder, and then heating, as in the cathode foil described in Patent Document 6. Instead, it is preferably formed using ion evaporation or other methods. This is because in a carbon particle layer formed using a binder, the underlying Ti or Al layer and the carbon are in point contact, which increases interfacial resistance and degrades adhesion. The carbon layer 5 is preferably formed as a smooth and dense carbon film.

The thickness of the metal layer 3, the mixed layer 4, and the carbon layer 5 can each be 0.005 μm or more and 0.01 μm or less. Furthermore, as shown in the performance test data described below, good cathode foil properties can be achieved when the total thickness of these three layers is 0.02 μm or more. However, each layer can also be made thicker.

Furthermore, the steps of forming the metal layer 3, the mixed layer 4, and the carbon layer 5 are preferably performed using the same film-forming method. This is because the simplified manufacturing process can significantly reduce manufacturing costs. However, each layer may be formed using a different method.

(Solid Electrolytic Capacitor of the Present Invention)

FIG. 2 is an exploded view showing a wound solid electrolytic capacitor 6 manufactured using the cathode foil 1 described above.

The wound solid electrolytic capacitor 6 can be manufactured by the following method:

(i) An anode foil 7 having an oxide film formed on the anode aluminum foil by chemical conversion treatment is overlapped with a cathode foil 8 having the layer structure shown in FIG1 via a separator paper 9, and an anode terminal 11 is connected to the anode foil 7, and a cathode terminal 12 is connected to the cathode foil 8, and then the capacitor assembly 10 is produced by winding the anode foil 7 and the cathode foil 8.

(ii) After the capacitor assembly 10 is housed in the aluminum case 13 , it is immersed in a mixed solution containing n-butanol as a diluent and iron (II) p-toluenesulfonate as an oxidant, and heated to form a solid electrolyte layer of polyethylenedioxythiophene by thermal polymerization.

The solid electrolyte layer may also be formed using a polypyrrole-based or polyaniline-based conductive polymer, or a TCNQ complex.

(Performance Test of the Solid Electrolytic Capacitor of the Present Invention)

First, cathode foils prepared as described above without roughening the aluminum foil, or cathode foils roughened for comparison, as well as cathode foils using Ti as the metal layer and cathode foils using Al as the metal layer, were prepared. Then, cathode foils having a coating thickness of 0.5 μm and 0.02 μm, consisting of a metal layer, a mixed layer, and a carbon layer, were prepared. Wound-type solid electrolytic capacitors having the structure shown in FIG. 2 were produced using these various forms of the cathode foils of the present invention, and the capacitance, ESR, and leakage current were measured. Furthermore, similar measurements were performed on wound-type solid electrolytic capacitors having the same structure as the capacitors of the present invention, except for the cathode foil, produced using cathode foils of known technology with different substrate and coating structures, and the test results were compared.

The structures of the cathode foils used in Conventional Examples 1 to 16 of the solid electrolytic capacitor and Examples 1 to 12 of the solid electrolytic capacitor of the present invention after comparative measurements are as follows.

(Known example 1)

A cathode foil made by etching a smooth aluminum foil.

(Known Example 2)

A cathode foil formed by forming a 0.5 μm Ti coating on a smooth aluminum foil.

(Known Example 3)

A cathode foil formed by forming a 0.02 μm Ti coating on a smooth aluminum foil.

(Known Example 4)

Cathode foil with a 0.5 μm thick TiN film formed on a smooth aluminum foil.

(Known Example 5)

This is a cathode foil made by forming a 0.02μm TiN film on a smooth aluminum foil.

(Known Example 6)

Cathode foil with a 0.5 μm TiC coating formed on a smooth aluminum foil.

(Known Example 7)

This is a cathode foil made by forming a 0.02μm TiC coating on a smooth aluminum foil.

(Known Example 8)

Cathode foil with a 0.5 μm carbon coating on a smooth aluminum foil.

(Known Example 9)

This is a cathode foil made by forming a 0.02μm carbon film on a smooth aluminum foil.

(Known example 10)

A cathode foil is made by forming aluminum carbide on a smooth aluminum foil and then fixing carbon particles (the film thickness varies depending on the position within the cathode foil surface, and is 0.5μm to 1μm).

(Known Example 11)

A cathode foil was prepared by etching a smooth aluminum foil to form a Ti coating of 0.25 μm and a carbon coating of 0.25 μm.

(Known Example 12)

A cathode foil was prepared by etching a smooth aluminum foil to form a Ti coating of 0.01 μm and a carbon coating of 0.01 μm.

(Known Example 13)

A cathode foil in which a Ti coating of 0.25 μm and a carbon coating of 0.25 μm are formed on a smooth aluminum foil.

(Known example 14)

A cathode foil in which a Ti coating of 0.01 μm and a carbon coating of 0.01 μm are formed on a smooth aluminum foil.

(Known Example 15)

A cathode foil in which a 0.25 μm Al coating and a 0.25 μm carbon coating were formed on a smooth aluminum foil.

(Known Example 16)

A cathode foil in which a 0.01 μm Al coating and a 0.01 μm carbon coating were formed on a smooth aluminum foil.

(Example 1)

A cathode foil was formed by etching a smooth aluminum foil to form a Ti coating of 0.2 μm, a Ti and carbon mixed layer a of 0.1 μm, and a carbon coating of 0.2 μm.

(Example 2)

A cathode foil having a Ti coating of 0.008 μm, a Ti and carbon mixed layer a of 0.004 μm, and a carbon coating of 0.008 μm was formed by etching a smooth aluminum foil.

(Example 3)

A cathode foil was prepared by forming a Ti coating of 0.2 μm, a Ti and carbon mixed layer a of 0.1 μm, and a carbon coating of 0.2 μm on a smooth aluminum foil.

(Example 4)

A cathode foil was prepared by forming a Ti coating of 0.008 μm, a Ti and carbon mixed layer a of 0.004 μm, and a carbon coating of 0.008 μm on a smooth aluminum foil.

(Example 5)

A cathode foil was prepared by forming a 0.2 μm Al coating, a 0.1 μm Al and carbon mixed layer a, and a 0.2 μm carbon coating on a smooth aluminum foil.

(Example 6)

A cathode foil was prepared by forming a 0.008 μm Al coating, a 0.004 μm Al and carbon mixed layer a, and a 0.008 μm carbon coating on a smooth aluminum foil.

(Example 7)

A cathode foil was formed by etching a smooth aluminum foil to form a Ti coating of 0.2 μm, a Ti and carbon mixed layer b of 0.1 μm, and a carbon coating of 0.2 μm.

(Example 8)

A cathode foil was formed by etching a smooth aluminum foil to form a Ti coating of 0.008 μm, a Ti and carbon mixed layer b of 0.004 μm, and a carbon coating of 0.008 μm.

(Example 9)

A cathode foil was prepared by forming a Ti coating of 0.2 μm, a Ti and carbon mixed layer b of 0.1 μm, and a carbon coating of 0.2 μm on a smooth aluminum foil.

(Example 10)

A cathode foil was prepared by forming a Ti coating of 0.008 μm, a Ti and carbon mixed layer b of 0.004 μm, and a carbon coating of 0.008 μm on a smooth aluminum foil.

(Example 11)

A cathode foil was prepared by forming a 0.2 μm Al coating, a 0.1 μm Al and carbon mixed layer b, and a 0.2 μm carbon coating on a smooth aluminum foil.

(Example 12)

A cathode foil was prepared by forming a 0.008 μm Al coating, a 0.004 μm Al and carbon mixed layer b, and a 0.008 μm carbon coating on a smooth aluminum foil.

The coatings formed on the substrate, except for the cathode foil of Known Example 10, were all formed using the aforementioned ion evaporation method. Specifically, the titanium nitride and titanium carbide coatings in Known Examples 4 to 7 were formed using titanium as an evaporation source in nitrogen and methane atmospheres, respectively. The carbon coatings in Known Examples 8 and 9 were formed using carbon as an evaporation source. As already explained, the coatings in Examples 1 to 12 were also formed using ion evaporation. While the mixed layer a in Examples 1 to 6 was formed with a uniform ratio of Ti or Al to carbon, the mixed layer b in Examples 7 to 12 was formed with a higher carbon ratio toward the upper layer. In Known Example 10, a manufactured and commercially available sample was used.

The results of the performance tests are shown in Table 1 below.

[Table 1]

In Table 1, cap. represents the capacitor's capacitance (unit: μF), ESR represents the equivalent series resistance (unit: mΩ), and LC represents the leakage current (unit: μA). Capacitance was measured at a frequency of 120 Hz. Equivalent series resistance was measured at a frequency of 100 kHz. Leakage current is the value measured after applying a rated 4 V DC voltage to the solid electrolytic capacitor for 3 minutes. The measurement results for capacitance, ESR, and leakage current shown in Table 1 are shown as bar graphs in Figures 3 to 5.

As shown in Table 1 and the bar graph in Figure 3, the measured capacitance values of Examples 1 to 12 are greater than those of Conventional Examples 1 to 16. Compared to the measured value (175.4 μF) of Conventional Example 1, which used an etched foil without a metal coating as the cathode foil, the capacitance of Examples 1 to 12 increased by approximately 60%. Furthermore, the capacitors of Conventional Examples 11 and 12 differed from Examples 1, 2, and 7 and 8 only in whether a mixed layer was formed between the Ti and carbon layers on the cathode foil (the capacitors of Examples 1, 2, and 7 and 8 differed only in whether the content of each component in the mixed layer of the cathode foil had a gradient). However, the measured values of Examples 1 and 2 (279.1 μF and 277.3 μF) and those of Examples 7 and 8 (282.1 μF and 280.1 μF) were greater than the measured values of Conventional Examples 11 and 12 (264.1 μF and 258.1 μF). Similarly, it was found that the measured values in Examples 3 to 6 and Examples 9 to 12, in which a new mixed layer was provided, were larger than the measured values in Conventional Examples 13 to 16. In particular, it was found that the measured values in Examples 7 to 12, in which the mixed layer had a gradient in component content by the above-mentioned method, were larger than the measured values in Examples 1 to 6, in which the mixed layer had no gradient in component content.

Furthermore, as shown in Table 1 and the bar graph in FIG4 , the measured ESR values of Examples 1 to 12 are lower than those of Conventional Examples 1 to 16. Compared to the measured value (12.32 mΩ) of Conventional Example 1, which used an etched foil without a metal coating as the cathode foil, the ESR of Examples 1 to 12 was reduced by approximately 60 to 65%. Furthermore, as already explained, the capacitors of Conventional Examples 11 and 12 differed from Examples 1, 2, and Examples 7 and 8 only in whether or not a mixed layer was formed between the Ti layer and the carbon layer in the cathode foil. However, the measured values of Examples 1 and 2 (4.76 mΩ and 4.82 mΩ) and those of Examples 7 and 8 (4.61 mΩ and 4.73 mΩ) were lower than the measured values of Conventional Examples 11 and 12 (6.43 mΩ and 7.10 mΩ). Similarly, it can be seen that the measured values in Examples 3 to 6 and Examples 9 to 12, in which a new mixed layer is provided, are smaller than the measured values in Conventional Examples 13 to 16. In particular, it can be seen that the measured values in Examples 7 to 12, in which the component content ratio of the mixed layer is provided with a gradient by the above-mentioned method, are smaller than the measured values in Examples 1 to 6, in which the component content ratio of the mixed layer does not have a gradient.

Furthermore, in the capacitors of Examples 11 and 12, 13 and 14, and 15 and 16, the cathode foils had the same coating structure, differing only in thickness (0.5 μm and 0.02 μm). However, as shown in Table 1 and the bar graph in Figure 4, in all cases, the ESR increased (by 0.3 mΩ to 0.7 mΩ) due to the thinning of the coating. In contrast, when comparing the ESR values of Examples 1 and 2, 3 and 4, and 5 and 6, which differed only in coating thickness, the measured value of Example 1 (4.76 mΩ) and the measured value of Example 2 (4.82 mΩ) were almost the same (this measurement result is presumably related to the roughening of the aluminum foil in Examples 1 and 2). However, the measured value of Example 4 (4.39 mΩ) was lower than the measured value of Example 3 (4.56 mΩ), and the measured value of Example 6 (4.37 mΩ) was lower than the measured value of Example 5 (4.51 mΩ). This tendency is also observed in Examples 7 to 12, where the mixed layer has a gradient in component content. Therefore, at least in the specific example where the aluminum foil is used without roughening, it can be understood that the cathode foil of the present invention is superior to the known ones in terms of maintaining good ESR characteristics even with a thin coating.

Furthermore, as shown in Table 1 and the bar graph in FIG5 , the leakage current values measured in Examples 1 to 12 are lower than those measured in Conventional Examples 1 to 16. Furthermore, the measured values in Examples 7 to 12, which include the mixed layer b, are lower than those in Examples 1 to 6, which include the mixed layer a. Comparing the measured values in Conventional Examples 11 to 16 with those in Examples 1 to 6 reveals that the provision of the mixed layer can reduce leakage current by approximately 20%. Furthermore, comparing the measured values in Examples 1 to 6, which include the mixed layer a, with those in Examples 7 to 12, which include the mixed layer b, reveals a reduction of approximately several percent.

Heat resistance test of the solid electrolytic capacitor of the present invention

Next, the capacitors of the conventional examples and the capacitors of the examples were subjected to a heat resistance test. The heat resistance test was conducted at 125°C, with a rated voltage of 4V applied to each of the capacitors of conventional examples 1 to 16 and examples 1 to 12 for 1000 hours. The capacitance and ESR values before and after the test were compared.

Table 2 below shows the electrostatic capacitance and ESR measured after the test for each capacitor, as well as the rate of change of these measured values before and after the test.

[Table 2]

In Table 2, ΔC/C is the rate of change in the capacitance measured before and after the test, expressed as a percentage: [(measured value after the test) - (measured value before the test)] / (measured value before the test). Similarly, ΔESR/ESR is the rate of change in the ESR measured before and after the test, expressed as a percentage. The pre-test values shown in Table 1 were used for calculating each rate of change. Furthermore, the rates of change in capacitance and ESR shown in Table 2 are shown as bar graphs in Figures 6 and 7.

First, the electrostatic capacitance after the heat resistance test was examined. As shown in Table 2, the measured capacitance values of Examples 1 to 12 were greater than those of Examples 1 to 16. In particular, the measured capacitance values of Examples 7 to 12 were greater than those of Examples 1 to 6. It can be seen that the capacitors of the present invention have a greater electrostatic capacitance than the known capacitors even after the heat resistance test. Furthermore, the rate of change of the measured capacitance values before and after the test was examined. As can be seen from Table 2 and Figure 6, this rate of change differs significantly between the known Examples 1 to 16 and Examples 1 to 12. Specifically, the heat resistance test reduced the measured capacitance values of the capacitors of Examples 11 and 12 by 3.8% and 4.5%, respectively. However, the heat resistance test reduced the measured capacitance values of the capacitors of Examples 1 and 2, which had a mixed layer therein, by 1.6% and 2.0%. Furthermore, the reduction rates of Examples 7 and 8 were only 0.9% and 1.3%. Similarly, it can be seen that the reduction rates in Examples 3 to 6 and Examples 9 to 12, in which a mixed layer is newly provided, are smaller than the reduction rates in the electrostatic capacitance measurement values in the known Examples 13 to 16. In particular, the reduction rates in Examples 9 to 12 are smaller than the reduction rates in Examples 3 to 6. It can be seen that the cathode foil of the present invention has better heat resistance than the known ones in terms of electrostatic capacitance characteristics.

The capacitance reduction rates in Examples 7 and 8 were 0.9% and 1.3%, respectively. In contrast, the capacitance reduction rates in Examples 9 and 10, where smooth aluminum foil was used as the cathode foil, were 0.7% and 0.3%. This indicates that, from the perspective of heat resistance, it is preferable not to etch the aluminum foil.

Furthermore, as shown in the bar graphs of Examples 3 to 6 and 9 to 10 in Figure 6, in these examples, a coating thickness of 0.02 μm can suppress the rate of decrease in the measured capacitance value to a lower level than a coating thickness of 0.5 μm. This means that when the cathode foil of the present invention is produced without etching the aluminum foil, a thinner coating is preferable from the perspective of heat resistance.

Next, the ESR after the heat resistance test was examined. As shown in Table 2, the measured ESR values for Examples 1 to 12 were lower than those for Conventional Examples 1 to 16. In particular, the measured ESR values for Examples 7 to 12 were lower than those for Examples 1 to 6. This shows that the capacitors of the present invention have lower ESR than conventional capacitors even after the heat resistance test. Furthermore, the rate of change in the ESR measured values before and after the test was examined. Table 2 and Figure 7 show that this rate of change differs significantly between Conventional Examples 1 to 16 and Examples 1 to 12. Specifically, while the increases in the ESR values of the capacitors of Examples 11 and 12 due to the heat resistance test were 18.8% and 25.4%, respectively, for the capacitors of Examples 1 and 2, which included the mixed layer a, the increases in the ESR values due to the heat resistance test were 2.5% and 2.3%, respectively. Furthermore, the increases in the ESR values of the capacitors of Examples 7 and 8, which included the mixed layer b, were only 2.2% and 2.1%, respectively. Similarly, the increases in the ESR values of Examples 3 to 6 and Examples 9 to 12, which included the newly included mixed layer, were smaller than those of the ESR values of Examples 13 to 16. In particular, the increases in the ESR values of Examples 7 to 12 were smaller than those of Examples 1 to 6. This indicates that the cathode foil of the present invention exhibits superior heat resistance in terms of ESR characteristics compared to the conventional examples.

The ESR increases in Examples 7 and 8 were 2.2% and 2.1%, respectively, whereas the ESR increases in Examples 9 and 10, where the cathode foil was made of smooth aluminum foil, were 0.5% and 0.2%. This indicates that, from the perspective of heat resistance, it is preferable not to etch the aluminum foil.

(Second embodiment)

The following describes a current collector having a first conductive layer composed of Ti or Al, a mixed layer composed of Ti or Al and graphite-like carbon (hereinafter sometimes referred to as GLC), and a second conductive layer composed of GLC formed on roughened aluminum foil, and a lithium-ion battery made using the current collector, as another embodiment of the present invention. However, as already described, the aluminum foil used as the base material of the current collector and the Ti or Al used to form the first conductive layer can be replaced by other materials, or as shown in the performance test data described below, the current collector of the present invention has good characteristics even without roughening the base material surface. In addition, as already described, the use of the current collector of the present invention is not limited to lithium-ion batteries, and the current collector can also be used as an electrode for any storage component such as other batteries, electric double-layer capacitors, hybrid capacitors, etc.

(Current Collector of the Present Invention)

FIG8 is a cross-sectional view showing the layer structure of current collector 19 according to one embodiment described above. Current collector 19 comprises: a metal foil 15, which is an aluminum foil roughened by electrochemical etching in an acidic solution; a metal layer 16 formed on metal foil 15 and comprising a metal coating of Ti or Al; a mixed layer 17 formed on metal layer 16 and comprising a mixture of Ti or Al and GLC; and a carbon layer 18 formed on mixed layer 17 and comprising GLC.

Commercially available high-purity aluminum foil can be used as the aluminum foil. The thickness of the aluminum foil is not particularly limited, but is preferably 5 μm to 50 μm in view of processability, electrical conductivity, weight, volume, cost, etc.

After placing a metal foil 15 and a metal material such as Ti or Al as an evaporation source in a vacuum reaction chamber, the Ti or Al is evaporated and ionized using an electron beam or plasma-generating electrode, and the generated metal cations are introduced to the metal foil 15 to form the metal layer 16. An example of a film formation method is physical vapor deposition (PVD) such as ion evaporation. In the embodiment where a layer composed of a nitride or carbide of a metal such as Ti or Al is formed on the metal foil 15, the first conductive layer can be formed by performing the above method in an ambient gas such as nitrogen or methane.

In addition, methods for forming the metal layer 16, that is, physical vapor deposition methods other than ion deposition, include vacuum deposition and sputtering. Chemical vapor deposition (CVD) methods such as thermal CVD, optical CVD, plasma CVD, and metal organic vapor deposition can also be used.

Mixed layer 17, like metal layer 16, can be formed by ion evaporation, for example. Specifically, a graphite material can be prepared as an evaporation source in addition to a metal material such as Ti or Al, and these two evaporation sources can be used simultaneously for film formation. The introduction of this mixed layer 17 improves the adhesion between the metal and the GLC, as well as its chemical stability, preventing degradation due to chemical reactions between the metals.

The mixed layer 17 is preferably configured to contain substantially only Ti or Al in the boundary region with the metal layer 16 and substantially only carbon (GLC) in the boundary region with the carbon layer 18. In particular, the GLC content continuously increases from the metal layer 16 toward the carbon layer 18. An example of such a mixed layer 17 can be formed as follows:

(i) When forming the mixed layer 17, the electron beam is irradiated only on the metal material to form a coating of only Ti or Al;

(ii) gradually reducing the electron beam exposure to the metal material over time while increasing the electron beam exposure to the graphite material, thereby forming a mixed film in which the metal and GLC are mixed and the GLC content increases toward the upper layer;

(iii) When film formation is completed, the electron beam exposure to the metal material is set to zero, so that only a GLC film can be formed. Alternatively, when forming the mixed layer 17 by sputtering, the mixed layer 17 can be formed in an optimal manner by any method, such as decreasing the voltage applied to the metal target (decreasing the sputtering rate of the metal target) or increasing the voltage applied to the graphite target (increasing the sputtering rate of the graphite target) over time.

In the performance test data described below, the data for Examples 1 to 4 were obtained using the above-mentioned ion deposition method, and using a current collector 19 in which the mixed layer 17 was formed in such a way that the GLC content continuously increased from the metal layer 16 toward the carbon layer 18. However, even if there are some areas in the mixed layer 17 where the GLC content decreases as it moves toward the carbon layer 18 (this situation may occur due to limitations in film formation technology, etc.), it is speculated that better characteristics can be obtained compared to current collectors with conventional technology. This is because even in such areas, the presence of Ti or Al and GLC improves the adhesion between the components, thereby preventing deterioration caused by chemical reactions such as oxidation of Ti or Al, and suppressing the contact resistance between the current collector and the electrode layer to a low level for a long period of time.

The carbon layer 18 can be formed by ion deposition, etc., similarly to the metal layer 16 and the mixed layer 17. Typically, in the process of forming the mixed layer 17, after the electron beam irradiation dose on the metal material is reduced to zero, the coating formation process is continued for a certain period of time while the electron beam is irradiated only on the carbon material, thereby forming the carbon layer 18.

The carbon layer 18 of the present invention is not formed by dispersing carbon particles in a binder such as a resin adhesive and then applying the binder. Instead, similar to the metal layer 16 and mixed layer 17 described above, it is preferably formed using a vapor deposition method such as ion deposition. This is because the carbon content in the carbon particle layer formed by kneading with the binder is reduced to the amount of binder that is substantially mixed. Furthermore, the contact between the underlying Ti or Al and the carbon particles is point contact. Furthermore, the aforementioned coating method makes it difficult to improve the electrical conductivity of the interface, resulting in increased interface resistance, poor adhesion, and difficulty in achieving uniform, thin coating. The carbon layer 18 is preferably formed as a smooth and dense GLC film.

The thickness of the metal layer 16, the mixed layer 17, and the carbon layer 18 can each be approximately 0.1 nm to 15 nm. If the combined thickness of at least these three layers is 0.3 nm or greater, excellent current collector properties can be achieved. However, each layer can be thicker without compromising electrical conductivity or economic efficiency. However, when roughening the metal foil, the combined thickness of these three layers is preferably 45 nm or less, taking into account uniform coverage of the inner walls of the pore structure.

Furthermore, the steps for forming the metal layer 16, the mixed layer 17, and the carbon layer 18 are preferably performed using the same film-forming method. This is because this simplifies the manufacturing process, improves productivity, and significantly reduces manufacturing costs. However, these layers may be formed using different film-forming methods within a range that does not compromise economic efficiency.

(Storage battery of the present invention)

FIG9 is a cross-sectional view showing a positive electrode 21 and a negative electrode 23 manufactured using the above-mentioned current collector 19 (the current collector used for the positive electrode is set as the positive electrode side current collector 19a, and the current collector used for the negative electrode is set as the negative electrode side current collector 19b). FIG10a and FIG10b are exploded views and external views showing an example of a lithium ion secondary battery 30 manufactured using these electrodes 21 and 23. The lithium ion secondary battery 30 can be manufactured by the following method:

(i) Interposed separator, stacking: A positive electrode 21 is formed on a current collector 19a, wherein an electrode layer ₂₀ is formed by kneading lithium iron phosphate (LiFePO4) as an active material, acetylene black as a conductive auxiliary agent, styrene-butadiene rubber as a binder, carboxymethyl cellulose ammonium salt as a thickening agent, and water. A negative electrode 23 is formed on a current collector 19b, wherein an electrode layer 22 is formed by kneading graphite as an active material, acetylene black as a conductive auxiliary agent, styrene-butadiene rubber as a binder, carboxymethyl cellulose ammonium salt as a thickening agent, and water. Then, a positive tab terminal 26 is connected to the positive-side current collector 19a, and a negative tab terminal 27 is connected to the negative-side current collector 19b. Then, these multiple tabs are stacked to produce a lithium-ion battery assembly 28.

(ii) After the lithium ion battery assembly 28 is housed in the case 29 , an electrolyte solution prepared by dissolving lithium hexafluorophosphate (LiPF ₆ ) as the electrolyte 25 in a mixed solution of ethylene carbonate and diethyl carbonate as an organic solvent is injected, and the case is sealed.

The materials or combinations of active materials, conductive additives, binders, and electrolytes used in the production of the battery, as well as the module structure (button type, wound type, laminated type, etc.) are not limited thereto.

(Performance Test of the Current Collector of the Present Invention)

The performance test of the current collector of the present invention is carried out on the following current collectors, namely, a current collector made of aluminum foil that has been roughened by electrochemical etching in an acidic solution as described above, and a current collector made of aluminum foil that has not been roughened as a base material. In each current collector, Ti or Al is used as the metal layer, and the thickness of the coating composed of the metal layer, the mixed layer, and the carbon layer is set to a total of 25 nm. For the purpose of improving the accuracy of the evaluation, the lithium-ion battery assembly used for performance evaluation uses the electrode formed by forming the above-mentioned electrode layer on the current collector as the positive electrode, and uses a lithium plate as the counter electrode to produce a button-type battery for performance testing. The button-type battery is used to measure and evaluate the discharge rate characteristics and charge-discharge cycle life characteristics of the positive electrode.

The discharge rate characteristics of the positive electrode were evaluated by performing the following charge and discharge cycles:

(i) the button-type battery is charged at a predetermined charging rate current value until it reaches 4.2 V, and then charged at a predetermined voltage value until the current value reaches 0.01 C.

(ii) Then, discharge the battery at a predetermined discharge rate until the battery reaches 3.0 V.

The discharge capacity at a discharge rate current value of 0.2C was used as a reference, and the capacity retention rate was calculated from the ratio of the discharge capacity of the button-type battery measured at each discharge rate current value (discharge capacity at each discharge rate current value [mAh/g] ÷ discharge capacity at a discharge rate current value of 0.2C [mAh/g] × 100) for evaluation. The ambient temperature was set at 25°C, and the discharge rate characteristics were evaluated while changing the above-mentioned discharge rate current value from 0.2C to 10C, and the capacity retention rate at each discharge rate current value was compared. When the discharge rate current value did not reach 1C, the above-mentioned predetermined charging rate current value was set to the same value as the discharge rate current value, and when the discharge rate current value was above 1C, it was fixed at 1C. Here, the so-called discharge rate current value of 1C means the current value that takes 1 hour to discharge the full capacity of the battery, and the so-called discharge rate current value of 10C means rapid discharge that discharges the full battery capacity within 6 minutes.

The charge and discharge cycle life characteristics of the positive electrode are evaluated by setting the ambient temperature to 25°C, fixing the charge rate current value and the discharge rate current value at 1C, and repeating the above charge and discharge cycles for 20 cycles. After each cycle is completed, the capacity retention rate is calculated based on the initial (first cycle) discharge capacity.

To verify the effect of roughening the metal foil on the adhesion strength between the current collector and the electrode layer, a SAICAS (Surface and Interfacial Cutting Analysis System) was used as an oblique cutting device for testing. A 1mm wide diamond-tipped blade was used to cut obliquely from the electrode surface at a constant speed (horizontally: 6μm/s, vertically: 0.6μm/s). After reaching the interface between the current collector and the electrode layer, the blade was moved horizontally at a constant speed (horizontally: 6μm/s). The horizontal stress applied to the blade at this time was used as the peel strength for comparison.

The structures of the current collectors used in Comparative Examples 1 to 7 of the storage batteries after comparative measurements and Examples 1 to 4 of the storage batteries of the present invention are as follows.

(Comparative Example 1)

The current collector consists of smooth aluminum foil.

(Comparative Example 2)

A current collector made by etching a smooth aluminum foil.

(Comparative Example 3)

A current collector formed by forming a 20nm thick graphite-like carbon film on a smooth aluminum foil.

(Comparative Example 4)

A current collector having a Ti coating of 12.5 nm and a graphite-like carbon coating of 12.5 nm formed on a smooth aluminum foil.

(Comparative Example 5)

A current collector having a Ti coating of 12.5 nm and a graphite-like carbon coating of 12.5 nm was formed on a smooth aluminum foil by etching.

(Comparative Example 6)

A current collector having a 12.5 nm thick Al coating and a 12.5 nm thick graphite-like carbon coating formed on a smooth aluminum foil.

(Comparative Example 7)

A current collector was formed by etching a smooth aluminum foil to form an Al coating of 12.5 nm and a graphite-like carbon coating of 12.5 nm.

(Example 1)

A current collector was formed by forming a Ti coating of 10 nm, a mixed layer of Ti and graphite-like carbon coating of 5 nm, and a graphite-like carbon coating of 10 nm on a smooth aluminum foil.

(Example 2)

A smooth aluminum foil was etched to form a current collector having a Ti coating of 10 nm, a mixed layer of Ti and graphite-like carbon coating of 5 nm, and a graphite-like carbon coating of 10 nm.

(Example 3)

A current collector was formed by forming a 10 nm thick Al coating, a 5 nm thick mixed layer of Al and graphite-like carbon coating, and a 10 nm thick graphite-like carbon coating on a smooth aluminum foil.

(Example 4)

A smooth aluminum foil was etched to form a current collector having an Al coating of 10 nm, a mixed layer of Al and graphite-like carbon coating of 5 nm, and a graphite-like carbon coating of 10 nm.

The film formation on the metal foil is performed by the above-mentioned ion vapor deposition method.

The test results of the discharge rate characteristics of the comparative examples and examples are shown in Tables 3 to 13. In addition, the capacity retention rates determined at each discharge rate current value for the comparative examples and examples are shown as a bar graph in FIG11 .

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 7]

[Table 8]

[Table 9]

[Table 10]

[Table 11]

[Table 12]

[Table 13]

11 , the discharge rate characteristics of Examples 1 to 4 using the current collectors of the present invention are significantly improved compared to the discharge rate characteristics when the current collectors of Comparative Examples 1 to 7 are used.

In addition, Tables 14 and 15 show the capacity retention rates determined at the end of one cycle of charge and discharge in Comparative Examples 1 to 7 and Examples 1 to 4, respectively, and are shown as bar graphs in FIG. 12 .

[Table 14]

Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Comparative Example 6 Comparative Example 7 1 (number of cycles) 100 100 100 100 100 100 100 2 95.5 99.2 99.5 99.6 99.7 99.7 99.8 3 89.7 98.4 99.2 99.0 99.3 99.1 99.4 4 82.5 97.1 98.8 98.6 98.9 98.8 99.0 5 75.3 95.4 97.8 97.0 97.8 97.1 97.9 6 68.6 93.3 95.0 96.1 97.0 96.0 97.2 7 61.8 90.9 93.1 95.2 96.1 95.2 96.4 8 55.5 88.4 92.3 94.3 95.2 94.4 95.6 9 49.7 85.6 90.1 92.5 93.4 92.6 94.0 10 44.3 82.2 87.8 90.8 91.7 91.0 92.1 11 38.8 79.4 85.3 88.9 89.9 89.2 90.2 12 33.4 76.8 82.9 87.9 89.0 88.1 89.3 13 28.6 74.0 80.1 87.0 88.3 87.2 88.7 14 24.3 71.6 77.0 85.1 86.8 85.5 87.0 15 20.6 69.0 74.8 83.9 84.9 84.0 85.2 16 17.3 65.9 70.4 82.7 83.8 82.8 84.1 17 14.4 62.4 66.7 81.0 82.1 81.3 82.5 18 11.8 60.0 64.8 79.1 80.8 79.2 81.2 19 9.9 57.9 61.9 78.0 79.3 78.3 80.1 20 7.4 55.5 58.9 75.9 78.6 76.1 79.6

[Table 15]

In Figure 12, compared with the charge and discharge cycle life characteristics when using the collectors of Comparative Examples 1 to 7, in which the capacitance retention rate decreases as the number of cycles increases, in Examples 1 to 4 using the collectors of the present invention, there is no decrease in capacitance until the 20th cycle, and it can be seen that the charge and discharge cycle life is significantly improved.

Figure 13 shows the results of a SAICAS test to evaluate the effect of roughening the metal foil on the adhesion strength between the current collector and the electrode layer for Comparative Examples 1 and 2 and Examples 1 and 2. Roughening the metal foil significantly improves the adhesion strength between the electrode layers, regardless of whether a coating is formed.

As described above, the electrodes produced using the current collector of the present invention show minimal degradation in quality caused by use at high discharge rates and repeated use for many times. This type of effect can be considered to be due to the fact that the current collector of the present invention has a coating structure as described above, so high electrical conductivity and chemical stability can be obtained on the interface, resulting in this type of effect. The improvement in electrical conductivity and chemical stability caused by the coating structure of the present invention is obviously affected by the specific use of the current collector. In view of this, when the current collector of the present invention is used on the negative electrode side of a lithium-ion battery, or on the positive electrode side or negative electrode side of an electric double-layer capacitor or hybrid capacitor, it can be inferred that quality degradation is also suppressed.

(Industrial Applicability)

The electrode material of the present invention can be used as cathode foil for wound or laminated solid electrolytic capacitors. Furthermore, the electrode material of the present invention can also be used in various capacitors operating with an electrolyte, including electrolytic capacitors, as well as electric double-layer capacitors, lithium-ion capacitors, lithium-ion batteries, and solar cells.

The current collector of the present invention can be used as an electrode for batteries, electric double layer capacitors, and hybrid capacitors. In addition, the current collector of the present invention can also be used in solar cells driven by electrolytes.

Claims (16)

1. An electrode material, characterized in that: On the electrode substrate, a first conductive layer containing metal, a mixed layer consisting of a substance constituting the first conductive layer containing metal and carbon, and a second conductive layer substantially composed of carbon are formed. The composition of the aforementioned mixed layer is such that, from the aforementioned first conductive layer containing metal toward the aforementioned second conductive layer, it changes from substantially containing only the components constituting the aforementioned first conductive layer containing metal to substantially containing only carbon. The aforementioned mixed layer has a portion that continuously changes from the aforementioned first conductive layer containing metal toward the aforementioned second conductive layer; The aforementioned first conductive layer containing metal contains a carbide of at least one metal selected from the group consisting of Ta, Ti, Cr, Al, Nb, V, W, Hf and Cu. 2. The electrode material as described in claim 1, wherein the aforementioned electrode substrate has not been roughened. 3. A solid-state electrolytic capacitor comprising a capacitor assembly, the capacitor assembly having: an anode foil and a cathode foil, a separator disposed between the anode foil and the cathode foil, and a solid electrolyte layer formed between the anode foil and the cathode foil, characterized in that: The electrode material described in claim 1 or 2 is used as the aforementioned cathode foil. 4. The solid electrolytic capacitor as claimed in claim 3, wherein the aforementioned solid electrolyte layer contains any one of: manganese dioxide ( _MnO2 ), tetracyanobenzoquinone dimethane (TCNQ), polyethylene dioxythiophene (PEDOT), polyaniline (PANI), and polypyrrole. 5. A current collector for an electrode, characterized in that: On a metal-containing substrate, a first conductive layer containing metal, a mixed layer consisting of a substance constituting the first conductive layer containing metal and carbon, and a second conductive layer substantially composed of carbon are formed. The composition of the aforementioned mixed layer is such that, from the aforementioned first conductive layer containing metal toward the aforementioned second conductive layer, the composition changes from substantially containing only the substance constituting the aforementioned first conductive layer containing metal to substantially containing only carbon. The aforementioned mixed layer has a portion that continuously changes from the aforementioned first conductive layer containing metal toward the aforementioned second conductive layer; The aforementioned first conductive layer containing metal contains a carbide of at least one metal selected from the group consisting of Ta, Ti, Cr, Al, Nb, V, W, Hf and Cu. 6. The current collector for an electrode as described in claim 5, wherein the aforementioned carbon is graphite-like carbon. 7. The current collector for electrodes as claimed in claim 5, wherein the substrate containing the aforementioned metal is a metal foil composed of any one of aluminum or aluminum alloy, Ti, Cu, Ni, Hf, and stainless steel. 8. The current collector for electrodes as claimed in claim 5, wherein the substrate containing the aforementioned metal is roughened. 9. A positive electrode for a non-aqueous electrolyte storage battery, comprising an electrode layer formed on a current collector for an electrode as described in any one of claims 5 to 8, the electrode layer comprising: an active material containing a transition metal oxide or a transition metal phosphate compound comprising any one of an alkali metal and an alkaline earth metal, a conductive additive, and a binder. 10. A negative electrode for a non-aqueous electrolyte storage battery, comprising an electrode layer formed on an electrode current collector according to any one of claims 5 to 8, the electrode layer comprising: a carbon material capable of absorbing or releasing any one of alkali metal ions and alkaline earth metal ions; an active material containing any one of Sn, Si or silicon oxide, S or sulfide, and titanium oxide; a conductive additive; and an adhesive. 11. A non-aqueous electrolyte storage battery, using at least one of the positive electrode of claim 9 and the negative electrode of claim 10. 12. An electrode for a non-aqueous electrolyte double-layer capacitor, wherein an electrode layer is formed on a current collector as described in any one of claims 5 to 8, the electrode layer comprising: an active material containing any one of activated carbon and carbon nanotubes; a conductive additive; and a binder. 13. A non-aqueous electrolyte double-layer capacitor, using the electrode of claim 12 as at least one of the positive and negative electrodes. 14. A positive electrode for a non-aqueous electrolyte hybrid capacitor, comprising an electrode layer formed on a current collector according to any one of claims 5 to 8, the electrode layer comprising: an active material containing any one of activated carbon and carbon nanotubes; a conductive additive; and a binder. 15. A negative electrode for a non-aqueous electrolyte hybrid capacitor, comprising an electrode layer formed on a current collector as described in any one of claims 5 to 8, the electrode layer comprising: a carbon material capable of absorbing or releasing any one of alkali metal ions and alkaline earth metal ions; an active material containing any one of Sn, Si or silicon oxide, S or sulfides, and titanium oxide; a conductive additive; and an adhesive. 16. A non-aqueous electrolyte hybrid capacitor, using at least one of the positive electrode of claim 14 and the negative electrode of claim 15.