JP2014150158A - Oxide structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oxide structure including an active material which improves conductivity, and increases specific capacity of a capacitor.SOLUTION: An oxide structure 1 includes a porous metal layer 2 and an oxide layer 3 disposed on both surfaces of the porous metal layer 2. An oxide is represented by a chemical formula: MOwhere M is different from a metal constituting the porous metal layer 2 and comprises at least one or more elements selected from Sn or transition metal including Mn, Co or Ni. The oxide may be any of MnO, CoO, NiO and SnO. Porous metal comprises any of Au, Ag and Cu, or a metal alloy including two or more of Au, Ag and Cu.

Description

  The present invention relates to an oxide structure and a manufacturing method thereof.

  Electrochemical supercapacitors that combine high power density and long life can be used as complementary energy storage elements for storage batteries and fuel cells in short pulse applications as well as main power.

  However, as the application expands, the energy density of the supercapacitor needs to be significantly improved (see Non-Patent Document 1).

  The specific capacity of a supercapacitor using ordinary carbon is usually 100 F / g to 120 F / g in the case of an organic electrode. The energy density is 4 Wh / kg to 5 Wh / kg, and this value is much smaller than that of a lead storage battery (26 Wh / kg to 34 Wh / kg) or a lithium ion battery (about 140 Wh / kg) (non-patent document). 2 and 3).

  In an electrochemical supercapacitor, a method for obtaining a high energy density is to use a metal oxide or a conductive polymer as a high capacity pseudocapacitance material as an electrode for storing electric charge. The hydrous ruthenium oxide has a large pseudo capacity and good reversibility (see Non-Patent Document 4). However, the high cost of ruthenium precursors limits commercial applications.

Manganese oxide (MnO ₂ ) is a promising material candidate because of its theoretically high specific capacity (1370 F / g), low cost, and environmental friendliness. A supercapacitor having a super-high capacity of 1000 F / g or more close to the theoretical value has been achieved in a water-soluble electrolyte (see Non-Patent Documents 5 and 6).

However, in order to realize a super capacitor using MnO _2, the MnO ₂ is a thin film, and the weight per unit area is required to consist of very small (10μg / cm ²⁾ nanoparticles. The obtained capacity was too small for commercial application (see Non-Patent Documents 7 and 8).

However, when the weight per unit area of MnO ₂ was increased with a thick film thickness (≧ 100 μg / cm ² , the thickness was about 1 μm), the specific capacity decreased dramatically. Specific capacities of 100 F / g to 300 F / g, which were smaller than 30% of the theoretical high capacity of MnO ₂ were obtained. This is mainly due to a loss of electron conductivity due to an increase in the film thickness of MnO ₂ (see Non-Patent Documents 9 to 13).

Further, for example, Patent Document 1 discloses that the characteristics of a capacitor are improved by a composite of ceramic and metal such as MnO ₂ .

WO2012 / 086697

B.E.Conway, Electrochemical supercapacitors, Kluwer Academic, Plenum Publisher, New York, 1999 A. Burke, Electrochim. Acta, 2007, 53, 1083 P. Simon, Y. Gogotsi, Nature Mater., 2008, 7, 845. J. P. Zheng, P. J. Cygan, and T. R. Zow, J. Electrochem. Soc., 1995, 142, 2699 M. Toupin, T. Brousse, D. Belanger, Chem. Mater., 2004, 16, 3184 X. Y. Lang, A. Hirata, T. Fujita, M. W. Chen, Nature Nanotechnology, 2011, 6, 232 J. N Broughton, M.J. Brett, Electrochim. Acta, 2004, 49, 4439 S.C.Pang, M.A.Anderson and T.W.Chapman, J. Electrochem.Soc., 2000, 147, 444 C.C.Hu, T.W.Tsou, Electrochem.Commun., 2002, 4, 105 P. Ragupathy, D. H. Park, G. Campet, H. V. Vasan, S.J. Hwang, J. H. Choy, N. Munichandraiah, J. Phys. Chem. C, 2009, 113, 6303 M. Xu, W Jia, S.J. Bao, Z. Su, B. Dong, Electrochim. Acta., 2010, 55, 5117 C. Xu, F. Kang, B Li, H. Du, J. Mater. Res., 2010, 25, 1421 M. Nakayama, T. Kanaya, R. Inoue, Electrochem. Commun., 2007, 9, 1154 JL Kang, A. Hirata, LJ Kang, XM Zhang, Y. Hou, LY Chen, C. Li, T. Fujita, K. Akagi, MW Chen, Angew. Chem. Int. Ed., DOI: 10.1002 / anie. 201208993 T. Fujita, PF Guan, K. McKenna, XY Lang, A. Hirata, L. Zhang, T. Tokunaga, S. Arai, Y. Yamamoto, N. Tanaka, Y. Ishikawa, N Asao, Y. Yamamoto, J Erlebacher, MW Chen, Nature Mater., 2012, 11, 775 W. Wei, X. Cui, W. Chen, D. G. Ivey, J. Power Sources, 2009, 186, 543 Z. Fan, J. Yan, T. Wei, L. Zhi, G. Ning, T. Li, F. Wei, Adv. Funct. Mater., 2011, 21, 2366 Y. Hou, Y. Cheng, T. Hobson, J. Liu, Nano Lett., 2010, 10, 2727 Y. Kang, B. Kim, H. Chung, W. Kim, Synthetic Met., 2010, 160, 2510 [19] K. R. Prasad, N. Miura, J. Power Sources, 2004, 135, 354 T. Xue, C. L. Xu, D.D. Zhao, X.H. Li, H.L. Li, J. Power Sources 2007, 164, 953 N. Nagarajan, H. Humadi, I. Zhitomirsky, Electrochem. Acta 2006, 51, 3039 Y. Wang, H. Liu, X. Sun, I. Zhitomirsky, Scripta Mater., 2009, 61, 1079 Y. Dai, K. Wang, J. Zhao and J. Xie, J. Power Sources, 2006, 161, 737 K. W. Nam and K. B. Kim, J. Electrochem. Soc., 2006, 153, A81 K. T. Lee, C. B. Tsai, W. H. Ho, N. L. Wu, Electrochem. Commun., 2010, 12, 686 Z. P. Feng, G. R. Li, J.H. Zhong, Z. L. Wang, Y. N. Ou and Y. X. Tong, Electrochem. Commun., 2009, 11, 706 Z. Xu, H. Du, B. Li, F. Kang, Y. Zeng, J. Electrochem. Soc., 2009, 156, A73

In conventional electrodes such as MnO ₂ , due to the high-speed oxidation-reduction reaction, the repetition life of the metal oxide electrode is limited by the mechanical deterioration of the electrode due to the volume change of the active layer of the oxide layer due to the cycle. . Therefore, there is a problem that no electrode is obtained by the thick MnO ₂ layer or the like having a high capacity and long life.

  In view of the above problems, an object of the present invention is to provide an oxide structure that has an active material that can improve conductivity and that can increase the specific capacity of a capacitor.

The present inventors have, in order to improve the capacity characteristics of the thick MnO ₂ film, Au, Ag, by forming an oxide such on both sides of the porous metal layer of the metal as Cu, the conductivity of MnO ₂ layer The present invention has been conceived with the knowledge that the enhancement of the above can be achieved.

To achieve the above object, an oxide structure of the present invention, a porous metal layer, an oxide layer disposed on both surfaces of the porous metal layer comprises an oxide, the table in the formula MO _X Unlike the metal of the porous metal layer, M is characterized by comprising at least one element selected from transition metals containing Sn, Mn, Co, and Ni or Sn.

In the above configuration, the oxide is preferably any one of MnO ₂ , Co ₃ O ₄ , NiO, and SnO ₂ .
The conductive metal is preferably made of Au, Ag, Cu, or a metal alloy containing two or more of these.

  The method for producing an oxide structure of the present invention comprises the steps of forming a porous metal layer and electrolytically depositing the oxide layer on the porous metal layer when producing any of the oxide structures described above. And a step of performing.

  The supercapacitor of the present invention is characterized by using any of the oxide structures described above as an electrode.

  The lithium ion battery of the present invention is characterized by using any of the oxide structures described above as an electrode.

  According to the oxide structure of the present invention, two oxide layers are formed symmetrically on both sides of the porous metal layer, so that the mechanical strength of the oxide structure is increased, and the electrons of the oxide layer are increased. For example, when used for an electrode of a supercapacitor, the specific capacity retention ratio can be increased even when the high specific capacity characteristics and charge / discharge are repeated.

It is a figure which shows typically the cross section of the oxide structure of this invention. It is an expanded sectional view showing an oxide structure of the present invention typically. (A) And (b) is a figure explaining the manufacturing method of an oxide structure. It is a figure which shows typically the porous gold | metal | money (NPG) of an Example. Is a diagram showing an apparatus for depositing a MnO ₂ layers of NPG. It is a figure which shows the optical image of the manufactured oxide structure. (A) ~ (f) are views showing an SEM image of electrochemically grow the MnO ₂ film on NPG. It is a diagram showing the relationship between weight and thickness per unit area of MnO ₂ layer to the electroplating time. (A) ~ (c) is a diagram showing a TEM image in bright field of MnO ₂ layer electrolytically formed on the NPG. It deposited thick MnO ₂ layers of XPS (X-ray photoelectron Spectroscopy) is a diagram showing the spectrum. FIG. 3 is a diagram illustrating a typical current voltage (CV) of an oxide structure. It is a figure which shows the relationship between the specific capacity which is the capacity | capacitance per unit mass, and sweep speed. It is a figure which shows the relationship between the internal resistance of the oxide structure of an Example, and current density. It is a figure which shows the relationship between the current density and specific capacity of the oxide structure of an Example. It is a figure which shows the current voltage (CV) of an oxide structure. It is a diagram showing the relationship between the weight of MnO ₂ layers of specific capacity and per unit area of the oxide structure. It is a schematic diagram which shows the structure of the super capacitor of an Example. It is a figure which shows the optical image of the produced super capacitor. It is a figure which shows the current voltage (CV) of a super capacitor. It is a figure which shows the relationship between the specific capacity which is the capacity | capacitance per unit mass, and sweep speed. It is a figure which shows the Nyquist plot of the electrochemical impedance measurement of a super capacitor. It is a figure which shows the cycling characteristics of a super capacitor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram schematically showing an oxide structure 1 of the present invention. As shown in FIG. 1, the oxide structure 1 of the present invention includes a porous metal layer 2 and an oxide layer 3 disposed on both surfaces of the porous metal layer 2. The oxide structure 1 of the present invention is also called a sandwich-structure active material or a sandwich-structure electrode because both surfaces of the porous metal layer 2 are covered with the oxide 3.

  The oxide that becomes the oxide layer 3 is a metal oxide that becomes an active substance of a battery or a supercapacitor. Such metals include transition metal elements, metal elements, etc., iron group elements, platinum group elements, copper group elements, zinc elements, aluminum group elements, manganese group elements, chromium group elements, earth metal elements, Examples thereof include titanium group elements, rare earth elements, alkaline earth metal elements, alkali metal elements, lanthanoids, actinoids, tin, lead, germanium, bismuth, and antimony.

  The pure metal oxide may further contain carbon group elements, nitrogen group elements, oxygen group elements, halogen, boron, and the like, which are typical nonmetallic elements.

Specific examples of the pure metal oxide include MnO ₂ , Co ₃ O ₄ , NiO, SnO ₂ , TiO ₂ , CeO ₂ , Al ₂ O ₃ , BaTiO ₃ , WO ₃ , In ₂ O ₃ , V ₂ O _{5. , Nb 2 O 5, Ta 2} O 5, taNbO 5, SiO 2, ZrO 2, LaCoO 3, LaCrO 3, LaMnO 3, Bi 2 O 3, SrCoO 3, PrMnO 3, SrTiO 3, BeO, MgSiO 3, Mg 2 SiO ₄ , Fe ₂ O ₃ , Fe ₃ O ₄ , ZnO, PbTiO ₃ , RuO ₂ , CrO _{2 and the} like can be mentioned. For example, when MnO ₂ , Co ₃ O ₄ , NiO, SnO ₂ is represented by the chemical formula (MO _X ), the subscript X attached to O is a number of 1 or more.

Examples of pseudocapacitive materials used in supercapacitors using metal oxides include MnO ₂ , TiO ₂ , CeO ₂ , and SnO ₂ among the above metal oxides.

  The conductive metal to be the porous metal layer 2 is preferably a material with low resistance such as Au, Ag, or Cu. The conductive metal 2 may be a metal alloy containing two or more of Au, Ag, and Cu. The porous metal layer 2 can be produced by dealloying a metal alloy containing two or more of Au, Ag, Cu and the like. Dealloying may be performed by etching a metal alloy containing two or more of Au, Ag, Cu or the like with an acid or the like.

FIG. 2 is an enlarged view schematically showing the oxide structure 1 of the present invention. As shown in FIG. 2, the MnO ₂ layer has a large number of pores inside the porous metal layer 2, and the oxide layer 3 has an outer surface and a back surface of the porous metal layer 2, that is, porous It is formed on both surfaces of the porous metal layer 2. The size of each hole in the porous metal layer 2 may be about 10 nm to 500 nm. The thickness of the porous metal layer 2 may be about 0.5 μm to 40 μm.

The thickness of the oxide structure 1 of the present invention may be selected according to the application, but may be, for example, 0.1 μm to 10 μm. The oxide structure 1 of the present invention can also be used as a supercapacitor electrode. In this case, the thickness of the oxide in the oxide structure 1 of the present invention can be, for example, 0.1 to 5 μm.

  Since the oxide structure 1 of the present invention has a sandwich structure as described later, the conductivity is improved. Thereby, in a capacitor such as a supercapacitor using the oxide structure 1 of the present invention, the specific capacity is increased as compared with an oxide not using the porous metal layer 2, and charging and discharging are repeated 3000 times, for example. Even later, it has an excellent feature that the specific capacity changes very little.

  The oxide structure 1 of the present invention includes a dielectric, a supercapacitor electrode (also referred to as an SC electrode), a lithium ion battery, an energy storage device, a backup power source such as a mobile phone or a personal computer, and electronic control of an automobile. It can be used for devices such as a backup power source of a device, a power supply device for automobiles, and a power storage device.

(Method for producing oxide structure)
An example of the manufacturing method of the oxide structure 1 will be described.
FIGS. 3A and 3B are diagrams illustrating a method for manufacturing the oxide structure 1.
First step (see FIG. 3A):
First, the porous metal layer 2 is formed on a polymer film or substrate (not shown). As the porous metal layer 2, a low resistance film such as Au or silver can be used. The porous metal layer 2 may be placed on a polymer film or substrate after it is formed.

Second step (see FIG. 3B):
Next, a pure oxide 3 having a predetermined thickness is formed on the porous metal layer 2. The pure oxide 3 can be formed by a wet method or a vapor deposition method. As the wet method, an electrochemical deposition method using a solution can be used. The pure oxide 3 may be a pore, that is, a porous film or a porous film.
The oxide structure 1 of this invention can be manufactured according to said process.
Hereinafter, the present invention will be described in more detail by way of examples.

In the present invention, the oxide layer 3 made of MnO ₂ is formed on both sides of the porous metal layer 2 made of nanometer-order porous gold (NPG) by an electrochemical deposition method. Hereinafter, the porous metal layer 2 will be described as NPG, and the oxide layer 3 will be described as a MnO ₂ layer.
Specifically, first, a porous metal layer 2 having a size of 18 mm × 20 mm × 700 nm (0.7 μm) was produced. The Ag ₆₅ Au ₃₅ (atomic ratio) alloy was etched with 69% nitric acid (HNO ₃ ). NPG2 was formed by etching (dealloying) Ag for 12 hours at room temperature. The pore size was about 50 nm. The remaining nitric acid in NPG2 was removed by washing with water.

FIG. 4 is a diagram schematically illustrating NPG 2 of the example. After producing NPG2 shown in FIG. 4, the NPG sheet was covered with cotton paper and placed on a substrate made of PET. In order to satisfactorily deposit MnO ₂ by electrolytic plating on NPG 2 to be described later, the coating of NPG ₂ with cotton paper and the pore size of NPG 2 larger than 40 nm, for example, This is an important elemental technique for forming the MnO ₂ layer 3 from these channels.

NPG2 held on a PET substrate is immersed in an aqueous solution of 0.2M (mol) Mn (CH ₃ COO) ₂ .4H ₂ O and 0.2M Na ₂ SO ₄ in a state of being covered with cotton paper. Then, the MnO ₂ layer 3 was deposited by an electrochemical method.

FIG. 5 is a diagram showing an example of an apparatus for depositing a MnO ₂ layer on NPG ₂ . As shown in FIG. 5, a potentiostat 10 manufactured by IVIU of the Netherlands having three terminals was used for depositing the MnO ₂ layer 3. Ag / AgCl was used for the reference electrode 11, and platinum was used for the counter electrode 12 and the working electrode 13 (see Non-Patent Document 14). These electrodes 11, 12, and 13 are inserted into a container 16 such as a beaker filled with an electrolytic solution 15. NPG 2 is connected to the working electrode 13. A process of applying a voltage of 0.40 V to the counter electrode 12 first for 10 seconds and then applying a voltage of 0.45 V for 20 seconds was repeated to deposit the MnO ₂ layer 3. Thus, the weight of the MnO ₂ layer 3 formed by the electrolytic plating method, that is, the electrochemical deposition method, is determined by integration of the total charge amount (coulomb: C) during electrolysis as a first measurement method (non- Patent Document 13) was obtained by weighing the weight of the MnO ₂ layer 3 formed as a _second measurement method in order to further increase the accuracy.

In the sandwich structure electrode of the oxide structure 1, the NPG film operates as a current collector and a good conduction path for electron conduction and ion conduction in order to realize the pseudocapacitance of MnO ₂ .

FIG. 6 is a diagram showing an optical image of the manufactured oxide structure 1. As shown in FIG. 6, in the sandwich electrode structure of the oxide structure 1, the NPG film operates as a current collector that collects current in order to realize the pseudocapacitance of MnO ₂ , and further, electronic conduction and ionic conduction. Operates as a good conduction path.

(Fine structure observation)
The fine structure of the oxide structure 1 includes a field emission scanning electron microscope (SEM, manufactured by JEOL (JEOL), JIB-4600F) and a scanning transmission electron microscope (STEM, manufactured by JEOL) JEM-2100F). The acceleration voltage of SEM is 15 kV.

FIGS. 7A to 7F are views showing SEM images of a film of MnO ₂ electrochemically grown on NPG ₂ . 7A to 7D, the electroplating time of MnO ₂ is 10 minutes for (a), 20 minutes for (b), 30 minutes for (c), and 40 minutes for (d), respectively.
Since the surface of the hole of NPG2 has a high density of steps and kinks, it is chemically active. Therefore, nucleation occurs when MnO ₂ is grown on NPG2 by electrolytic plating on the surface of the hole of NPG2. It is easy (see Non-Patent Document 15). Thereby, the growth of MnO ₂ having a nanostructure starts in the channel of the nanopore of NPG2 in the first stage of electroplating (see FIG. 7A).
When active internal surface of the nanoporous is completely coated with MnO _2, MnO ₂ nanostructures begin to grow out of the nanoporous, and grow symmetrically into two outer surfaces of the NPG sheet, and NPG2, A sandwich structure composed of two layers of thick MnO ₂ film is formed on the surface of NPG 2 (see FIGS. 7A to 7D).

It can be seen from the SEM image at a high magnification (about 90,000 times) that the thick MnO ₂ layer 3 is porous and continuously grows from the pores of NPG ₂ (see FIG. 7 (e)).
From SEM image of a thick MnO ₂ layer 3 on the surface, the thick MnO ₂ layer 3 is found to be porous (see FIG. 7 (f)).

FIG. 8 is a diagram showing the relationship between the weight per unit area (μg / cm ² ) and the thickness (nm) of the MnO ₂ layer 3 with respect to the electroplating time (unit: minutes). The thickness was measured by an SEM image of the cross section of the MnO ₂ layer 3.
As shown in FIG. 8, the weight per unit area of the MnO ₂ layer 3 increases almost linearly with the electrolytic plating time, and becomes about 200 μg / cm ² after 40 minutes.
From the measurement of the thickness of the MnO ₂ layer 3, during the first 15 minutes, the MnO ₂ layer 3 mainly grows into a nanoporous channel of NPG _{2 and} the weight per unit area of the MnO ₂ layer 3 is about 72 μg / cm 3. ² . After 15 minutes, the film thickness gradually increases, and after 40 minutes, the film thickness is about 2.1 μm.

From the measurement of the thickness of the MnO ₂ layer 3, during the first 15 minutes, the MnO ₂ layer 3 mainly grows into a nanoporous channel of NPG _{2 and} the weight per unit area of the MnO ₂ layer 3 is about 72 μg / cm 3. ² . After 15 minutes, the film thickness gradually increases, and after 40 minutes, the film thickness is about 2.1 μm.

A more detailed microstructure of the electroplated MnO ₂ layer 3 was examined with a transmission electron microscope (TEM). 9A to 9C are diagrams showing TEM images in a bright field of the MnO ₂ layer 3 formed by electrolytic plating on the NPG ₂ .
As shown in FIG. 9A, the electrolytically formed MnO ₂ layer 3 is composed of a plurality of thin sheets having a thickness of several nm.

From the scanning transmission electron microscope (STEM) image (about 10 million times) shown in FIG. 9B, each thin sheet constituting the MnO ₂ layer 3 is polycrystalline, and the size of each nanograin is about It was found to be 4 nm.
The inset of FIG. 9 (a) is an electron diffraction pattern, the nanopolycrystal is cubic, and its lattice constant is MnO ₂ of a reported rock salt structure with defects (see Non-Patent Document 16). And agrees well.

As shown in FIG. 9 (c), a high-resolution TEM image (approximately 7.5 million times) shows the interface between MnO ₂ and NPG ₂ , and the MnO ₂ layer 3 made of nano-polycrystal has a conventional MnO _{2 structure.} Similarly to the complex of NPG2 and NPG2 (see Non-Patent Document 6), it can be seen that it is chemically bonded to the ligament of Au.

The chemical level of the MnO ₂ layer 3 was measured by XPS (AxIS-ULTRA-DLD). X-rays in the XPS measurement are 150 W Al Kα rays, and the degree of vacuum is 10 ⁻⁷ Pa.

FIG. 10 is a diagram showing an XPS (X-ray photoelectron spectroscopy) spectrum of the deposited thick MnO ₂ layer 3. In the figure, the horizontal axis represents binding energy (eV), and the vertical axis represents signal intensity (CPS).
As is clear from FIG. 10, in the XPS spectrum, two peaks of 642.8 eV and 654.6 eV were observed in the binding energy. These two peaks are related to the Mn ⁴⁺ Mn 2p _3/2 and 2p _1/2 orbitals, respectively. No peak related to Mn ²⁺ was measured. From the measured value of 1s orbit of O (oxygen), the average valence of Mn was 3.8, which was consistent with the reported MnO _{2 of} the rock salt structure.

Electrochemical measurement (CV) was performed by the three-terminal method. The distance between the working electrode 13 and the counter electrode 12 was about 2 mm. The measurement was performed in an aqueous solution of 2M LiSO ₄ . The voltammetry (CV) cycle characteristics were measured at a potential of 0.8 V by changing the sweep rate. The stability of the cycle was measured with a sweep rate of 50 mV / s in the voltammetric cycle measurement.

FIG. 11 is a diagram showing a typical current voltage (CV) of the oxide structure 1. In the figure, the horizontal axis represents voltage (V), and the vertical axis represents current (A / cm ² ). The sweep speed is 5 mV / second (s) to 100 mV / second (s). MnO ₂ is formed by electrolytic deposition for 20 minutes, and the weight per area is 90 μg / cm ² .
As shown in FIG. 11, there is no resistive state in the CV curve, and the CV curve having a rectangular symmetry is shown even when the sweep speed is 100 mV / s.

FIG. 12 is a diagram showing the relationship between the specific capacity (F / g), which is the capacity per unit mass, and the sweep speed. In the figure, the horizontal axis represents the sweep speed (mV / s), and the vertical axis represents the specific capacity (F / g).
As shown in FIG. 12, when the sweep rate is 5 mV / s, the specific capacity is about 841 F / g, and when the sweep speed is 100 mV / s, the specific capacity is about 510 F / g, and this value is shown below. This is a larger value than the oxide structures using various MnO ₂ reported so far.
(1) In the oxide structure composed of MnO ₂ and graphene, the sweep rate was 2 mV / s and the specific capacity was about 310 F / g (see Non-Patent Document 17).
(2) The oxide structure composed of MnO ₂ , carbon nanotube, and conductive polymer had a sweep rate of 500 mV / s and a specific capacity of about 427 F / g (see Non-Patent Document 18).
(3) The oxide structure composed of MnO ₂ , carbon nanotubes, and paper had a sweep rate of 2 mV / s and a specific capacity of about 540 F / g (see Non-Patent Document 19).

(Comparative Example 1)
Furthermore, the oxide structure of Comparative Example 1 was compared. In the oxide structure of Comparative Example 1, an Ag ₆₅ Au ₃₅ sheet is formed on an Au film having a thickness of 50 nm formed on PET and is not dealloyed, that is, an Ag ₆₅ Au ₃₅ sheet that is not made porous. This is an electrode on which an MnO ₂ layer 3 is formed by electrolytic plating. The specific capacity of Comparative Example 1 in which the weight of the MnO ₂ layer 3 per unit area was the same was significantly lower than that of the example of the present invention.

From the above results, the large specific capacity of the oxide structure 1 of the example is attributed to the fact that the conductivity of electrons and ions is clearly enhanced by the sandwich structure electrode. The sandwich electrode has a large contact area between the inner and outer surfaces of the NPG 2 between the nanocrystals of the MnO ₂ layer 3 and the highly conductive gold ligament (beam). Furthermore, the channel in which the NPG 2 is opened for the transport of the electrolyte effectively utilizes the MnO ₂ layer 3 deposited on both sides of the NPG ₂ for charge accumulation. Thus, according to the oxide structure 1 of Example, while maintaining high specific capacity, becomes possible to increase relative to conventional MnO ₂ layer 3 a weight per unit area more than three times.

FIG. 13 is a diagram illustrating the relationship between the internal resistance and the current density of the oxide structure 1 of the example. In the figure, the horizontal axis represents current density (A / g), and the vertical axis represents internal resistance (Ω). As is clear from FIG. 13, the internal resistance when the current density was 1 A / g was reduced to about 50% of that of Comparative Example 1. Thus, it can be seen that the resistance of the oxide structure 1 of the example is small because NPG2 is used instead of the Ag ₆₅ Au ₃₅ sheet unlike the comparative example 1.

A high specific capacity was also confirmed in the charge / discharge characteristics.
FIG. 14 is a diagram illustrating the relationship between the current density and the specific capacity of the oxide structure 1 of the example. In the figure, the horizontal axis represents current density (A / g), and the vertical axis represents specific capacity (F / g). As is clear from FIG. 14, when the current density is increased from 0.25 A / g to 20 A / g, the specific capacity decreases from 702 F / g to 355 F / g and then becomes a constant specific capacity. .

FIG. 15 is a diagram showing a current voltage (CV) of the oxide structure 1 of the present invention. The horizontal axis of the figure is the same as FIG. The sweep rate is 50 mV / s, and the deposition time of MnO ₂ is changed from 5 minutes to 40 minutes.
As is apparent from FIG. 15, even when the electrolytic deposition time is 40 minutes and the weight of the MnO ₂ layer 3 per unit area is about 200 μg / cm ² , the CV curve is rectangular, that is, the thick MnO ₂ layer 3 It is shown that the transport of electrons and ions that are easy to use at high speed can be obtained.

FIG. 16 is a diagram showing the relationship between the specific capacity of the oxide structure 1 and the weight of the MnO ₂ layer 3 per unit area. In the figure, the horizontal axis represents the weight per unit area (μg / cm ² ), and the vertical axis represents the specific capacity (F / g). The sweep speed is 5 mV / s for the circle (◯) and 50 mV / s for the square (□).
As is clear from FIG. 16, when the weight of the MnO ₂ layer 3 per unit area is 53 μg / cm ² , the specific capacity of about 916 F / g, which is about 70% of the theoretical value, can be realized.

FIG. 16 also shows the specific capacity value of the MnO ₂ layer 3 reported for comparison. Table 1 shows the specific capacities reported in Non-Patent Documents 8, 10, 20 to 27, and the sweep speed during measurement. FIG. 16 and Table 1 show that the specific capacity of the conventionally reported MnO ₂ layer 3 is smaller than that of the oxide structure 1 of the present invention.

As shown in FIG. 16, when the weight of the MnO ₂ layer 3 per unit area is further increased, the specific capacity decreases. However, in the oxide structure 1 of the example, a high specific capacity of 772 F / g was obtained even when the MnO ₂ layer 3 was thick, that is, the weight of the MnO ₂ layer 3 per unit area was about 128 μg / cm ² . . This specific capacity is 2 to 5 times the specific capacity of the MnO ₂ layer 3 deposited on a flat Au layer having the same weight of the MnO ₂ layer 3 per unit area or the above-mentioned conventional documents. Is the value of

In the oxide structure 1 of the example, even when the weight of the MnO ₂ layer 3 per unit area is about 200 μg / cm ² , that is, about 2.1 μm, a high ratio of about 550 F / g at a sweep rate of 5 mV / s. Gained capacity. This value is sufficient for storing energy at a high specific capacity.

Furthermore, in the oxide structure 1 of the example, the dependency of the specific capacity on the sweep rate is not large. For example, when the MnO ₂ layer 3 is electroplated for 30 minutes, the sweep rate is 50 mV / s and the specific capacity is only reduced from 665 f / g to 557 F / g. This is because the electron and ionic conductivity of thick MnO ₂ enhanced by NPG2 promotes kinetically faradic reduction and oxidation reactions even at high sweep rates.

(Super capacitor using oxide structure)
A supercapacitor 20 using the oxide structure 1 of the example was manufactured.
FIG. 17 is a schematic diagram illustrating the structure of the supercapacitor 20 of the example, and FIG. 18 is a diagram illustrating an optical image of the manufactured supercapacitor 20.
As shown in FIG. 17, the supercapacitor 20 of the embodiment has a structure in which a separator 22 is inserted between two oxide structures 1 and an electrolyte solution 24 is filled between the two oxide structures 1. doing.

In the supercapacitor 20 shown in FIG. 18, the weight of the MnO ₂ layer 3 per unit area as the oxide structure 1 is 200 μg. In the oxide structure 1, the MnO ₂ layer 3 is deposited on both sides of the NPG ₂ , but the porosity inside the NPG ₂ and the deposited MnO ₂ layer 3 facilitate the conduction of electrons and ions. The redox reaction occurs simultaneously on both sides of the electrode for full utilization of the active material during charge accumulation.

FIG. 19 is a diagram showing the current voltage (CV) of the supercapacitor 20. In the figure, the horizontal axis represents voltage (V) and the vertical axis represents current (A). The sweep speed is 5 mV / s to 100 mV / s. MnO ₂ is formed by electrolytic deposition for 20 minutes, and the weight per area is 200 μg / cm ² .
As shown in FIG. 19, there is no resistive state in the CV curve, and a rectangularly symmetric CV curve is shown.

FIG. 20 is a diagram showing the relationship between the specific capacity (F / g), which is the capacity per unit mass, and the sweep speed. In the figure, the horizontal axis represents the sweep speed (mV / s), and the vertical axis represents the specific capacity (F / g).
As shown in FIG. 20, it can be seen that the sweep rate is 5 mV / s and the specific capacity is about 580 F / g. This value coincides with the measurement result obtained by performing the oxide structure 1 by the three-terminal method. A good capacity characteristic of the supercapacitor 20 using the oxide structure 1 is that the oxidation-reduction reaction of the oxide structure 1 also operates in the two-terminal device, and the electrolyte is freely transported throughout the device. Is shown.

FIG. 21 is a diagram showing a Nyquist plot of the electrochemical impedance of the supercapacitor 20. The horizontal axis in the figure is the real axis (Ω), and the vertical axis is the imaginary axis (Ω). The AC amplitude is 50 mV, and the measurement frequency is 0.1 Hz to 100 kHz. The figure also shows a Nyquist plot of a supercapacitor made using the oxide structure of Comparative Example 1.
As shown in FIG. 21, the semicircle on the high frequency side (see arrow (←) in FIG. 21) relates to the charge transfer resistance at the interface between the electrode and the electrolyte or the intrinsic charge transfer resistance of the porous electrode ( Non-patent document 28). The electrode of the oxide structure 1 exhibits a very small radius. This indicates that charge transfer in the electrolyte is highly efficient.
On the other hand, on the low frequency side, it is an ideal straight line along the imaginary axis. This indicates that the diffusion resistance is small. The series resistance (also expressed as iR and Rs) of the supercapacitor of the comparative example is 14.75Ω, which is found to be much larger than the series resistance of the supercapacitor of the example. Thereby, also in the impedance measurement of the supercapacitor 20, it is shown that MnO ₂ which is the active material of the oxide structure 1 is completely used for the oxidation-reduction reaction with high charge accumulation efficiency.

(Super capacitor cycle characteristics)
FIG. 22 is a diagram showing the cycle characteristics of the supercapacitor 20. In the figure, the horizontal axis represents the number of cycles, and the vertical axis represents the capacity retention rate (%). The sweep speed is 50 mV / s.
As is clear from FIG. 22, the capacity retention after 3000 cycles was about 97.1%. In the cycle characteristics of the comparative example measured at the same sweep rate, the capacity retention after 1000 cycles was 75%, which was a significantly smaller value than in the example.

There are the following two mechanisms for explaining the mechanism for reducing the capacity of an electrode using MnO ₂ (see Non-Patent Document 16).
(1) The MnO ₂ layer 3 is partially dissolved in the electrolyte during the cycle.
(2) The MnO ₂ layer 3 gradually fails mechanically during the cycle.

The electrolyte used for the supercapacitor 20 of the example and the comparative example 1 and the operating parameters are the same. That is, since the electrolytes of the example and the comparative example 1 are the same, it is likely that the MnO ₂ layer 3 is partially dissolved in the electrolyte, so that the same cycle characteristics are obtained. Therefore, in the mechanism (1), the difference in cycle characteristics between the supercapacitor 20 of the embodiment and the comparative example cannot be well explained.

Comparing the flat non-porous Ag ₆₅ Au ₃₅ sheet of the comparative example with NPG 2 of the oxide structure 1, the NPG 2 is porous, so it is far more than the flat Ag ₆₅ Au ₃₅ sheet of the comparative example. It has a large curved surface area, that is, a porous inner wall surface and apertures. Specific binding between the MnO ₂ which is coated on the outer surface of the MnO ₂ and NPG2 grown from the nano-holes of NPG2, the mechanical stability of the thick MnO ₂ layer 3 to improve the stability of the cycle characteristic Can enhance sex. The symmetrical structure of the oxide structure 1 and the excellent interface contact between the Au and the MnO ₂ layer 3 maintain a balance of microscopic stress induced by the volume change cycle of the MnO ₂ layer 3. This increases cycle stability. Thereby, the reason why the cycle stability of the example is higher than that of the comparative example is considered to be due to the above-mentioned (2), which is a mechanism for reducing the capacity of the electrode using MnO ₂ .

  This cycle stability is comparable to electric double layer capacitors using carbon, which is the most stable in electrochemical energy storage systems.

In the oxide structure 1 of the present invention, not only the conductivity is improved and the resistance is reduced, but also the MnO ₂ layer 3 is formed on both sides of the NPG ₂ , the mechanical strength is increased, and the thick MnO ₂ layer 3 is formed. The cycle stability of the specific capacity of the supercapacitor 20 using can be improved.

  According to the above embodiment of the present invention, it is possible to improve the capacity characteristics of an oxide made of a transition metal for the supercapacitor 20 or the lithium ion battery.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention described in the claims, and it goes without saying that these are also included in the scope of the present invention. .

1: Oxide structure 2: Porous metal layer 3: Oxide layer 4: Substrate 10: Potentiostat 11: Reference electrode 12: Counter electrode 13: Working electrode 15: Electrolytic solution 16: Container 20: Supercapacitor 22: Separator 24 : Electrolyte

Claims (6)

A porous metal layer, and an oxide layer disposed on both sides of the porous metal layer,
Including
The oxide is represented by the chemical formula MO _X, M, unlike the metal constituting the porous metal layer, consisting of at least one or more elements Mn, Co, selected from transition metals or Sn containing Ni An oxide structure characterized by that. The oxide structure according to claim 1, wherein the oxide is any one of MnO ₂ , Co ₃ O ₄ , NiO, and SnO ₂ .   2. The oxide structure according to claim 1, wherein the porous metal layer is made of one of Au, Ag, and Cu or a metal alloy including two or more thereof. A method for producing an oxide structure according to any one of claims 1 to 3,
Forming the porous metal layer;
Electrolytically depositing the oxide layer on the porous metal layer;
The manufacturing method of the oxide structure characterized by including.   A supercapacitor using the oxide structure according to claim 1 as an electrode.   A lithium ion battery using the oxide structure according to claim 1 as an electrode.