JP6202435B2 - Porous alloy compound, method for producing the same, and electric double layer capacitor - Google Patents

Description

  The present invention relates to a porous alloy compound, a method for producing the same, and an electric double layer capacitor.

  Since electric double layer capacitors have the advantages of high power density, high speed charge / discharge, and long life, research and development has been conducted from various angles (for example, Patent Document 1).

JP 2012-033899 A

Conway, B. E. Electrochemical supercapacitors: Scientific Fundamentals and Technological Applications, Kluwer, 1999 Gogotsi, Y. & Simon, P. True performance metrics in electrochemical energy storage, Science, 334, 917-918, 2011 LeRoy, R. L., Bowen, C. T. & LeRoy, D. J., The thermodynamics of aqueous water electrolysis. J. Electrochem. Soc., 127, 1954-1962, 1980 Armand, M., Endres, F. D., MacFarlane, R., Ohno, H. & B. Scrosati, Ionic-liquid materials for the electrochemical challenges of the future, Nat. Mater., 8, 621-629, 2009 Hasan, M., Jamal, M. & Razeeb, K. M., Coaxial NiO / Ni nanowire arrays for high performance pseudocapacitor applications, Electrochim. Acta., 60, 193-200, 2012 Wang, G., Huang, J., Chen, S., Gao, Y. & Cao, D., Preparation and supercapacitance of CuO nanosheet arrays grown on nickel foam, J. Power Sources, 196, 5756-5760, 2011 Kang, J. L. et al. Enhanced supercapacitor performance of MnO2 by atomic doping. Angew. Chem. Int. Ed., 52, 1664-1667, 2013 Lee, H. Y. & Goodenough, J. B. Supercapacitor behavior with KCl electrolyte, J. Solid State Chem., 148, 81-84, 1999 Yan, J. et al. Advanced Asymmetric supercapacitors based on Ni (OH) 2 / graphene and porous graphene electrodes with high energy density, Adv. Funct. Mater., 22, 2632-2641, 2012 Fischer, AE, Pettigrew, KA, Rolison, DR, Stroud, RM & Long, JW Incorporation of homogeneous, nanoscale MnO2 within ultraporous carbon structures via self-limiting electroless deposition: Implications for electrochemical capacitors., Nano Lett., 7, 281- 286, 2007 Chmiola, J. et al. Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer, Science, 313, 1760-1763, 2006 Chmiola, J., Largeot, C., Taberna, P. L., Simon, P. & Gogotsi, Y. Monolithic carbide-derived carbon films for Micro-supercapacitors. Science 328, 480-483, 2010 Zhu, Y. et al., Carbon-based supercapacitors produced by activation of graphene, Science, 332, 1537-1541, 2011 Lang, X. Y., Hirata, A., Fujita, T. & Chen, M. W. Nanoporous metal / oxide hybrid electrodes for electrochemical supercapacitors, Nat.Nanotech. 6, 232-236, 2011 Wang, G., Zhang, L. & Zhang, J., A review of electrode materials for electrochemical supercapacitors Chem. Soc., Rev. 41, 797-828, 2012 Simon, P. & Gogotsi, Y., Materials for electrochemical capacitors, Nat. Mater., 7, 845-854, 2008

  On the other hand, since the electric double layer capacitor has an energy density that is an order of magnitude smaller than that of a lead storage battery, a window with a low specific capacity and a narrow operating potential is generated (see Non-Patent Documents 1 and 2).

The energy density (E) of the electrochemical electric double layer capacitor is given by the following equation by the capacitance (C) and the stable operating voltage (V).
E = 0.5CV ²

  For most electrodes, the potential window of the aqueous electrolyte will usually not exceed 1.2V. This is limited by the thermodynamic potential of the aqueous electrolyte (see Non-Patent Document 3).

  Although the potential window of a non-aqueous electrolyte is wider than that of an aqueous electrolyte, the potential window of a non-aqueous electrolyte is often lower than the withstand voltage of the aqueous electrolyte (pseudocapacitive material). (See Patent Document 4).

  Therefore, for high-energy and high-power applications, a new material with high specific capacity and high withstand voltage, which can charge and discharge at high speed with high energy and high specific capacity, is equivalent to or exceeds the storage battery, is required. (See Non-Patent Document 2).

In the conventional modification methods of MnO ₂ by doping, most of the systems are composed of metal cations / MnO ₂ , and the improvement of electronic conductivity and capacity has not been clarified.

  In view of the above problems, the present invention has a first object to provide a porous alloy compound capable of obtaining a high potential window, and a second object to provide a method for producing a porous alloy compound. A third object is to provide an electric double layer capacitor using a porous alloy compound.

The present invention provides the following formula (1):
^{_{(Ni II a Cu I b Cu}} II c Mn II d Mn IV e) O f (OH) g (H 2 O) h (1)
(In the formula (1), a, b, c, d, e, f, g and h are 0 or a positive number satisfying a + b + c + d + e + f + g + h = 100, respectively, d + e> a, d + e> b + c, 20 ≦ a + b + c + d + e ≦ 40, 20 <f <40, 20 <g <40)
It is a porous alloy compound represented by these.
In the above configuration, the average pore diameter of the porous alloy compound is preferably 0.1 to 10 nm.
The X-ray diffraction pattern preferably has peaks close to Cu, Ni and Mn and 2θ = 36.5 ° and 2θ = 61.6 °.
A method for producing a porous alloy compound according to any one of the above, wherein Step 1 of producing a porous alloy by de-alloying an alloy composed of Mn, Ni, and Cu; To obtain a porous alloy compound by polarization.
In the above configuration, the porous alloy compound is preferably a thin film.
The porous alloy has the following formula (2):
_{Mn x -Ni y -Cu z (2} )
(In the formula (2), x, y and z are positive numbers satisfying x + y + z = 100, x ≦ y, x ≦ z, and 10 ≦ x ≦ 30)
You may have the structure represented by these.
In step 1, the alloy is immersed in a solution of at least one compound selected from the group consisting of ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), NaCl, KCl, Na ₂ SO ₄ and K ₂ SO ₄ to de-alloy. To obtain a porous alloy.
The alkaline solution is preferably KOH, NaOH, or LiOH.
The present invention is an electric double layer capacitor using the porous alloy compound described above as a polarizable electrode. A porous alloy compound may be used as the collector electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the electrical double layer capacitor using the porous alloy compound from which a high electric potential window is obtained, the manufacturing method of a porous alloy compound, and a porous alloy compound can be provided.

It is a figure which shows typically the structure of the electric double layer capacitor using the porous alloy compound of this invention. It is sectional drawing which shows typically the electric double layer capacitor using the porous alloy compound of this invention. (A)-(e) is a figure explaining the manufacturing method of the porous alloy compound in this invention. Ternary alloy consisting of porous Ni _36.5 Cu _36.5 Mn ₂₇ where the polarization is a diagram showing X-ray diffraction of the ternary alloys of ternary alloy and NiCuMn consisting NiCuMn porous to (XRD). It is a figure which shows the scanning transmission microscope (STEM) image of the porous alloy compound in this invention. It is a figure of HAADF (high angle scattering annular dark field) of a STEM image. It is a figure which shows the result after the inverse fast Fourier transform of FIG. 6, (a) is an inverse fast Fourier transform image, (b) is explanatory drawing of (a). It is a figure which shows the measurement result of XPS of a porous alloy compound. The sweep speed is 50 mV / s, and the voltage ranges are -0.4 V to 0.6 V, -0.6 V to 0.6 V, -0.8 V to 0.6 V, -1.1 V to 0.6 V, -1. It is a figure which shows the repeated charging / discharging characteristic of the porous alloy compound in this invention measured by changing into 15V-0.65V. It is a figure which shows the repetitive charging / discharging characteristic of the porous alloy compound in this invention when sweeping speed is 3 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 30 mV / s, 40 mV / s. It is a figure which shows the repetitive charging / discharging characteristic (CV characteristic) of an electric double layer capacitor when a sweep rate is 3 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 30 mV / s, 40 mV / s. . It is a figure which shows the charging / discharging characteristic of an electric double layer capacitor. It is a figure which shows the specific capacity of an electrical double layer capacitor. It is a figure which shows the spectrum of the energy dispersion spectroscopy (also called Energy Dispersion Spectroscopy, EDS) measured by the X-ray analysis of the porous alloy compound in this invention. (A) is the STEM image of the EELS measurement location, (b) is the EELS spectrum on the low energy side, and (c) is the EELS spectrum on the high energy side. It is a figure which shows the lagone plot of the electric double layer capacitor of Example 1. FIG. It is a figure which shows the Nyquist plot of the electrochemical impedance of an electric double layer capacitor. It is a figure which shows the cycling characteristics of an electrical double layer capacitor. It is a figure which shows the scanning transmission microscope (STEM) image after polarization of the porous alloy compound of the comparative example 1, and an inset is a limited field electron diffraction (SAED) image. The CV curve of the porous alloy compound of the comparative example 1 is shown. It is a figure which shows the CV curve in the sweep rate from which an electric potential window differs from -0.4V to 0.5V. 4 is a SEM image of a de-alloyed CuMn binary alloy of Comparative Example 2. FIG. 4 is a SEM image of a CuMn binary alloy after polarization in Comparative Example 2. FIG. 4 is a diagram showing an X-ray diffraction (XRD) of a porous alloy compound of Comparative Example 2. FIG.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
From the viewpoint of achieving a high potential window, the porous alloy compound of the present invention includes at least the metal M ₁ and the metal M ₂ (however, the metal M ₂ does not include the metal M ₁ ). And an oxide of the metal M _{1 and} an oxide of the metal M ₂ ,
The metal M ₁ is Mn and / or V, and the metal M ₂ is at least two metals selected from the group consisting of transition metals.
Incidentally, for example, if the metal _{M 1} is Mn, the metal _{M 2} Mn is not selected, if the metal _{M 1} is V, the metal _{M 2} V is not selected, the metal _{M 1} is at Mn and V if, Mn and V as the metal _{M 2} is not selected.

From the viewpoint that the reaction efficiency is better when the surface area per weight is increased,
The average pore size of the porous alloy compound is preferably from 0.1 to 10 nm, more preferably from 0.1 to 5 nm, still more preferably from 0.1 to 3 nm, still more preferably from 0.3 to 1 nm. The average pore size of the porous alloy is determined by calculating the specific surface area from the amount of pure nitrogen adsorbed on the surface after heating in vacuum at 120 ° C. for 3 hours in accordance with the BET method, and desorbing the adsorbate. The average pore diameter was determined from the desorption isotherm, which is the relationship between the relative pressure and the adsorption amount.

  From the same viewpoint, the porous alloy preferably has an average pore size such that a porous alloy compound obtained by subjecting the porous alloy to a dealloying method has the above-mentioned preferred average pore size.

From the viewpoint that the oxide has a high pseudo-electric capacity,
The metal M ₁ preferably contains at least Mn, more preferably Mn,
The metal M ₂ is preferably at least one metal selected from the group consisting of Ni, Cu, Cr, Fe and Co, more preferably at least 2 selected from the group consisting of Ni, Cu, Cr, Fe and Co. It is a seed metal, more preferably Ni and / or Cu, and still more preferably Ni and Cu.

From the viewpoint that the compound of water and oxygen has higher pseudo-electric capacity,
The porous metal compound is preferably the following formula (1):
^{_{(Ni II a Cu I b Cu}} II c M 1 II d M 1 IV e) O f (OH) g (H 2 O) h (1)
(In the formula (1), a, b, c, d, e, f, g, and h are 0 or a positive number satisfying a + b + c + d + e + f + g + h = 100, respectively)
A compound represented by
More preferably, the metal M ₁ is at least Mn
More preferably, the metal M ₁ is Mn, and d + e> a, d + e> b + c,
More preferably, 20 ≦ a + b + c + d + e ≦ 40, 20 <f <40, 20 <g <40.

From the viewpoint that the oxide has a high pseudo-electric capacity,
In the porous alloy compound of the present invention, it is preferable that Mn and O form an oxide (preferably MnO) and are included in the porous alloy compound, and that MnO forms a rock salt crystal. More preferred.

From the viewpoint of having a crystal structure with high structural stability,
The porous alloy compound in the present invention preferably has a peak close to Cu, Ni and Mn and 2θ = 36.5 ° and 2θ = 61.6 ° in the X-ray diffraction pattern.

A porous alloy compound represented by the formula (1) is schematically shown in FIG.
A preferred porous alloy compound 1 in the present invention has a porous Cu and / or Ni metal skeleton 2 on the order of nm, and the metal skeleton 2 includes an oxide-hydroxide 3 made of MnO or the like. It is thought that it has.

An electric double layer capacitor of the present invention is schematically shown in FIG.
The electric double layer capacitor 10 of the present invention is composed of the porous alloy compound 1 of the present invention, the polarizable electrode 12 including the first and second polarizable electrodes 12a and 12b, and the first and second polarizable electrodes. The separator 13 is inserted in order to prevent a short circuit with 12a and 12b, and the electrolytic solution 14 is inserted between the first and second polarizable electrodes 12a and 12b. In the present invention, when it is not necessary to distinguish the first and second polarizable electrodes 12a and 12b, they are also simply referred to as polarizable electrodes 12.

  Since the first polarizable electrode 12a using the porous alloy compound 1 of the present invention has a porous Cu and / or Ni metal skeleton 2 of the order of nm, the first polarizable electrode 12a can be self-supporting. May also serve as the collector electrode 15. Alternatively, the collector electrode 15 may be connected to the first polarizable electrode 12a.

  Similarly to the first polarizable electrode 12a, the second polarizable electrode 12b using the porous alloy compound 1 of the present invention has a porous Cu and / or Ni metal skeleton 2 on the order of nm, so that it is self-supporting. The second polarizable electrode 12b may also serve as the collector electrode 15. Alternatively, the collector electrode 15 may be connected to the second polarizable electrode 12b.

  As the separator 13, a nonwoven fabric made of glass fiber, cellulose, or the like can be used.

  The electrolyte 14 can be an aqueous electrolyte. Examples of the aqueous electrolyte include an aqueous solution containing KOH.

According to the electric double layer capacitor 10 in which the porous alloy compound 1 of the present invention is used for the polarizable electrode 12 and the aqueous electrolyte 14 is used, a high specific capacity of 627 Fcm ⁻³ (1493 Fg ⁻¹ ), 1.8 V A high potential window is obtained. Thereby, according to the electric double layer capacitor 10 of the present invention, a high energy density and a specific capacity can be obtained in a high potential window by a plurality of redox reactions (also referred to as redox reactions).

The porous alloy compound in the present invention can be produced as follows.
That is, the manufacturing method of the porous alloy compound of the present invention is from the viewpoint of achieving a high potential window,
The alloy consists of metal M ₁ and a metal M ₂ and de-alloying step 1 to produce a porous alloy,
And the step 2 of polarizing the porous alloy with an alkaline solution to obtain the porous alloy compound.

  In this case, the porous alloy compound is preferably a thin film from the viewpoint of weight because it is used as an electrode, and the thickness of the thin film is preferably 10 to 100 μm, more preferably 20 to 80 μm, still more preferably 20 to 40 μm. It is.

In the method for producing a porous alloy compound of the present invention,
From the viewpoint of solid solubility with Mn, the porous alloy has the following formula (2):
_{Mn x -Ni y -Cu z (2} )
(In the formula (2), x, y and z are positive numbers satisfying x + y + z = 100, x ≦ y, x ≦ z, preferably 10 ≦ x ≦ 30, more preferably 20 ≦ x ≦ 30)
It is preferable that it has the structure represented by these.

In the method for producing a porous alloy compound of the present invention, from the viewpoint of achieving a high potential window,
In Step 1, at least one compound selected from the group consisting of ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), NaCl, KCl, Na ₂ SO ₄ , KCl and K ₂ SO _{4 is used} to form an alloy, preferably a thin film of the alloy. It is preferable to immerse in a solution of

A method for producing a porous alloy compound in the present invention will be described with reference to FIGS.
As shown in FIG. 3 (a), an alloy thin film 4 made of NiCuMn is first prepared and dealloyed (see FIG. 3 (b)) to obtain a porous material having many nm-order pores. Alloy 5, that is, porous NiMnCu is formed (see FIG. 3C). The alloy thin film 4 can be produced by a die-casting method or the like. The dealloying can be preferably performed using an acid solution, a solution of at least one compound selected from the group consisting of NaCl, KCl, Na ₂ SO ₄ , KCl, and K ₂ SO ₄ .
Next, the porous Ni-Mn-Cu alloy 5 is polarized (see FIG. 3D) to produce the porous alloy compound 1 (see FIG. 3E) in the present invention. . Polarization can be preferably performed using an alkaline solution containing an OH group such as KOH, NaOH, or LiOH.

The porous alloy compound 1 of the present invention shown in FIG. 3 has a valence in which an oxide-hydroxide 3 is mixed with metal cations, compared with a conventional material for an electric double layer capacitor. A hydroxide 3 is supported by a metal skeleton 2 having high conductivity.
Thus, the porous alloy compound 1 of the present invention shown in FIG. 3 has high electrical conductivity for fully utilizing the high specific capacity of the oxide-hydroxide 3. The high specific capacity is due to multiple redox reactions at different potentials due to the effective utilization of multiple cations in the material.

According to the electric double layer capacitor 10 using the porous alloy compound 1 of the present invention, compared with the electric double layer capacitor using the conventional pseudo-electric capacitive material, the oxidation potential is increased in combination with the high potential window of 1.8V. -The high power density can be maintained by the hydroxide 3 to provide a high energy density.
Like the oxide, the oxide-hydroxide 3 is fragile and fragile in the charge / discharge process, but the electrode using the oxide-hydroxide 3 of the present invention has an unusually high cycle retention characteristic. Yes. This cycle retention characteristic is because the fragile oxide-hydroxide 3 is mechanically accommodated in a channel composed of pores in the nanometer (nm) order of the metal skeleton 2 which is another component.

  The porous alloy compound 1 of the present invention is suitable as a material for an electric double layer capacitor, preferably as a pseudo-electric capacitive material.

The electric double layer capacitor 10 of the present invention includes:
From the viewpoint of increasing the capacity of the electric double layer capacitor, the specific capacity is preferably 500 to 2000 F / g, more preferably 1200 to 1700 F / g, and further preferably 1300 to 1600 F / g.
From the viewpoint of increasing the energy density of the electric double layer capacitor, the energy density is preferably 5 to 30 Wh / kg, more preferably 10 to 20 Wh / kg, and further preferably 12 to 15 Wh / kg.

  The electric double layer capacitor 10 of the present invention is also effective for next-generation energy storage. Hereinafter, the present invention will be described in more detail with reference to examples.

(Production of Ribbon made of Ni ₁₅ Cu ₁₅ Mn ₇₀ )
A ribbon which is a thin film of an alloy made of Ni ₁₅ Cu ₁₅ Mn ₇₀ (composition is atomic%) having a thickness of about 20 μm and a single phase was prepared. This ribbon has a thickness of 99,999% or more of Ni, Cu, and Mn dissolved in a quartz tube in an induction furnace, and then the molten alloy is poured into a rotating copper wheel. Was cast so as to be 20 μm. The dimensions of the ribbon are 15 mm × 3 mm × 20 μm.

The ribbon is demetalized using a 1M (mol) (NH ₄ ) ₂ SO ₄ solution to desorb unstable Mn, and a ternary alloy composed of Ni _36.5 Cu _36.5 Mn ₂₇ is obtained. It was. Demetalization was performed by applying −0.7 V to the reference electrode using a potentiostat manufactured by IVIU in the Netherlands having 3 terminals. The reference electrode was Ag / AgCl, and the counter electrode was platinum.

Next, polarization was performed. Polarization was carried out using a 1M (mol) KOH solution and the above potentiostat under conditions of 0.9 V for 20 seconds and then 0.8 V for 40 seconds.
By de-alloying, Mn which is not stable was eliminated, and a ternary alloy composed of Ni _36.5 Cu _36.5 Mn ₂₇ was obtained. The dealloying was performed by applying −0.7 V to the reference electrode using a potentiostat manufactured by IVIU of the Netherlands having three terminals.

The average pore size of a ternary alloy composed of Ni _36.5 Cu _36.5 Mn ₂₇ , that is, a porous alloy is about 5 nm. The average pore size was determined by purifying the surface by heating in vacuum at 120 ° C. for 3 hours in accordance with the BET method (calculation formula by Brunauer, Emmett and Teller (1938)) and then adsorbing pure nitrogen on the surface. The specific surface area was determined from the amount, and the average pore diameter was determined from the desorption isotherm, which is the relationship between the relative pressure when the adsorbate desorbs and the amount of adsorption.

  On the other hand, the average pore diameter according to the BET method of the porous alloy compound of the present invention obtained by dealloying the above porous alloy was 0.6 nm.

FIG. 4 is a diagram showing an X-ray diffraction (XRD) of a ternary alloy composed of polarized porous Ni _36.5 Cu _36.5 Mn ₂₇ . The horizontal axis in FIG. 4 is an angle (°), that is, an angle corresponding to twice the incident angle θ of the X-ray on the atomic plane, and the vertical axis indicates the X-ray diffraction intensity (arbitrary scale).
As is clear from FIG. 4, it was found that the polarized ternary alloy 1 made of porous Ni _36.5 Cu _36.5 Mn ₂₇ has a monolithic face-centered cubic lattice (FCC) structure.

  In order to oxidize the porous alloy, 1 M KOH was used at room temperature, and polarization was performed at 0.9 V to produce the porous alloy compound 1 of the present invention.

  FIG. 5 is a view showing a scanning transmission microscope (STEM) image of the porous alloy compound 1 of the present invention. As shown in FIG. 5, the nanoporous passage of the porous alloy compound 1 of the present invention is completely filled with a leaky polarized product having a pore diameter of 1 nm or less. The inset of FIG. 5 is a limited field electron diffraction (SAED) image. This inset shows that the polarized nanoporous material has two crystalline phases. One is a synthesized oxidized phase having a cubic structure, and the rest is a face-centered cubic lattice metal.

The oxidation phase has a close crystallographic relationship with the nanoporous metal substrate.
FIG. 6 is a HAADF (high angle scattering annular dark field) of a STEM image. HAADF (High-Angle Angular Dark-Field) is a kind of STEM dark field method.
It can be seen from the HAADF of the STEM image shown in FIG. 6 that the two crystal phases have different lattice constants and contrasts.

  FIG. 7 is a diagram illustrating the result after the inverse fast Fourier transform of FIG. 6, (a) is an inverse fast Fourier transform image, and (b) is an explanatory diagram of (a). The inverse fast Fourier transform was performed using a representative image of the oxide and metal phase. As shown in FIG. 7, the distribution of the oxide included in the metal skeleton and the porous metal skeleton can be clearly seen.

  The oxide volume fraction was approximately 60-70%. The oxide is confined within the pore channels in the remaining nanoporous alloy. The nanoporous alloy has a three-dimensional porous opening.

The crystal structure of the porous alloy compound 1 of the present invention was examined in more detail by XRD.
As shown in FIG. 4, the porous alloy compound 1 formed by polarizing a porous alloy has two weak and broad peaks with 2θ of 36.5 ° (P1) and 61.6 ° (P2). Observed. These peaks are derived from diffraction from (111) and (220) planes having a rock salt type oxide and a lattice constant of 0.426 nm (4.26 Å). This lattice constant is just between the lattice constant of 0.445 nm (4.45 Å) of MnO, which is a well-known rock salt type oxide, and the lattice constant of NiO, 0.418 nm (4.18 Å). Considering that the nanoporous precursor is composed of three elements of Cu, Ni and Mn, the single-phase oxide is likely to contain a plurality of metal cations. This leads to a large shift in lattice constant from pure MnO or NiO.

In order to determine the chemical composition and the charged state of the oxidized phase, the composition was examined by X-ray photoelectron spectroscopy (also called Xray Photoelectron Spectroscopy, XPS).
For the XPS measurement, a Shimadzu Kratos device (Axis-ultra DLD) was used. As the X-ray source, monochromatic Al Kα ray was used. The output was a voltage of 15 kV and a current of 10 mA. The analysis area is 700 μm × 300 μm. In order to remove the adsorbed material on the outermost surface, an argon ion beam was used to cut away from the outermost surface to a depth of 5 nm by sputtering. The surface of the porous alloy compound 1 from which the adsorbed material on the outermost surface was removed was subjected to composition analysis by XPS.

FIG. 8 is a graph showing the XPS measurement results of the porous alloy compound 1. The horizontal axis of the figure is the binding energy (eV), and the vertical axis is the signal intensity (arbitrary scale). The inset shows enlarged views in the vicinity of binding energies of 530 eV, 640 eV, 860 eV, and 930 eV, respectively.
As shown in FIG. 8, the peaks of Mn2p, Ni2p, Cu2p and O1s were detected by XPS. Details of these peaks are shown in the inset of FIG.
On the other hand, low binding energy peaks corresponding to the metal levels of Mn, Ni, and Cu were not detected.

  From the above XPS measurement results, the porous alloy compound 1 is completely covered with an oxidation phase having a considerable volume ratio, which is consistent with the observation results of the STEM images in FIGS. 6 and 7.

  As is apparent from the inset of FIG. 8, from the peaks of Mn2p, Ni2p and Cu2p, the valence of Mn is divalent and tetravalent, the valence of Ni is bivalent, the valence of Cu is monovalent and bivalent, respectively. It turned out to be. In O1s, there are two distinct peaks with binding energies of 529.5 eV and 531.3 eV, and a weak shoulder peak with 533.1 eV. These peaks are peaks peculiar to oxygen contained in metal oxide (metal-oxygen-metal) and hydroxide (metal-OH), respectively.

  By combining the XPS measurement result, the scanning transmission electron microscope, and the XRD measurement result, the oxide in the porous alloy compound 1 of the present invention has a rock salt structure and has a plurality of compositions. It turns out that it becomes the hydroxide which number mixed.

The composition formula of the porous alloy compound 1 of the present invention is determined by deconvolution of each peak and integration in the XPS spectrum, and is shown in the following formula (3).
(Ni ^II _5.7 Cu ^I _3.9 Cu ^II _6.1 Mn ^II _12.3 Mn ^IV _9.2 ) O _28.3 (OH) _32.3 · 2.2H ₂ O (3)
The composition is shown in Table 1.

When the porous alloy compound 1 of the present invention is compared with a precursor made of Ni _36.5 Cu _36.5 Mn _27, it can be seen that the relative composition of Mn in the oxide is clearly increased. From this, it is presumed that Mn is selectively oxidized during polarization, so that Mn-rich (Mn-rich) oxide-hydroxide 3 is formed. Thereby, from the measurement results of XRD and limited-field electron diffraction image (also referred to as SAED), the oxide-hydroxide 3 consisting of a plurality of components and represented by the above chemical formula (2) is a single crystal phase. It is not a physical mixture of oxides of Ni, Cu and Mn.

A potentiostat consisting of three electrodes was used to evaluate the electrochemical properties of the porous alloy compound 1 containing the oxidation-hydroxide 3 of the present invention.
FIG. 9 is a diagram showing repetitive charge / discharge characteristics of the porous alloy compound 1 of the present invention measured at various voltage ranges at a sweep rate of 50 mV / s. In the figure, the horizontal axis represents voltage (V), and the vertical axis represents current (A). Using a potentiostat manufactured by IVIU in the Netherlands having 3 terminals, -0.7 V was applied to the reference electrode. The reference electrode was Ag / AgCl, and the counter electrode was platinum. As the electrolytic solution, a 1M KOH aqueous solution was used.
In FIG. 9, the potential window is -0.4V to 0.6V, -0.6V to 0.6V, -0.8V to 0.6V, -1.1V to 0.6V, -1.15V to. The measurement was changed to 6V. As shown in FIG. 9, it can be seen that the porous alloy compound 1 of the present invention has a plurality of redox peaks in voltammetry (CV). The most prominent redox peak occurs at a potential window of 0.11V to 0.47V. This peak is the same as that of NiO (see Non-Patent Document 5).

  However, the other peaks of the porous alloy compound 1 of the present invention do not completely match the redox behavior in monolithic Cu and Mn oxides (see Non-Patent Documents 6 and 7). When the potential window was expanded to −1.15 V, no significant increase in cathode current was observed other than the kinetically reversible redox peak. As a result, it was found that the electrode using the porous alloy compound 1 of the present invention is stable against a reversible reduction reaction and a hydrogen releasing reaction.

  The electrode using the porous alloy compound 1 of the present invention has a large potential window of −1.15 V to 0.65 V, which has not been obtained conventionally, in an aqueous solution, and is electrochemically stable. The potential window of −1.15 V to 0.65 V is a value far exceeding the theoretical potential window of water (see Non-Patent Document 3).

FIG. 10 shows the repetitive charge / discharge characteristics of the porous alloy compound 1 of the present invention when the sweep rate is 3 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 30 mV / s, and 40 mV / s. FIG.
As shown in FIG. 10, all the oxidation peaks shift to the high potential side and the reduction peaks shift to the low potential side as the sweep rate increases. This indicates that the redox reaction for charge accumulation is a diffusion control process. The diffusion control process is the same as monolithic Ni and Cu oxides, eg oxides such as CuO and NiO (see Non-Patent Documents 5, 6 and 9).

(Electric double layer capacitor)
Next, an electric double layer capacitor 10 using the porous alloy compound 1 of the present invention will be described.
In the electric double layer capacitor 10, the porous alloy compound 1 of the present invention was used as the polarizable electrode 2, and the electrolyte solution 14 was a 1M KOH aqueous solution.
FIG. 11 shows the repetitive charge / discharge characteristics (CV characteristics) of the electric double layer capacitor 10 when the sweep rate is 3 mV / s, 5 mV / s, 10 mV / s, 20 mV / s, 30 mV / s, and 40 mV / s. FIG. In the figure, the horizontal axis represents voltage (V), and the vertical axis represents current (A).
As shown in FIG. 11, the repeated charge / discharge characteristics (CV characteristics) of the electric double layer capacitor 10 clearly show the same behavior of the electric double layer capacitor 10 as that measured by the three-terminal method.

  FIG. 12 is a diagram showing the charge / discharge characteristics of the electric double layer capacitor 10. In the figure, the horizontal axis represents time (seconds), and the vertical axis represents voltage (V). As shown in FIG. 12, the charge / discharge characteristics of the electric double layer capacitor 10 clearly show the behavior of the electric double layer capacitor.

  The volume for the calculation of the specific capacity is based on the polarizable electrode 2 including all of the oxidation-hydroxide 3, the inactive metal skeleton 2 and the nanopore openings.

FIG. 13 is a diagram showing the specific capacity of the electric double layer capacitor 10. In the figure, the horizontal axis represents current density (Ag ⁻¹ ), the left vertical axis represents specific capacity (Fg ⁻¹ ), and the right vertical axis represents specific capacity (Fcm ⁻³ ).
As shown in FIG. 13, the maximum specific capacity of the electric double layer capacitor was about 627 Fcm ^{−3 at} a low current density of 0.25 Acm ⁻³ . This value is the largest specific capacity of the electric double layer capacitor as far as the present inventors know, and is a large value of 4 to 12 times that of a carbon material such as activated carbon (see Non-Patent Documents 2 and 13). The specific capacity is larger than the high-performance material of the electric double layer capacitor (see Non-Patent Document 10).

As the current density increases, the specific capacity of the electric double layer capacitor 10 gradually decreases due to a decrease in utilization efficiency of the porous alloy compound 1 due to charge / discharge of a high current of charge / discharge. However, the specific capacity is 300 Fcm ⁻³ even in a high current region.

For comparison with other pseudo-capacitive materials having good performance, the mass of the porous alloy compound 1 was determined by measurement such as energy dispersion spectroscopy (referred to as EDS) and XPS.
FIG. 14 is a diagram showing an EDS (energy dispersive spectroscopy) spectrum measured by X-ray analysis of the porous alloy compound 1 of the present invention. In the figure, the horizontal axis represents energy (keV), and the vertical axis represents the X-ray count. When the atomic weight% (at%) of the constituent element of the porous alloy compound 1 is obtained from the EDS spectrum of FIG. 14, Mn is 24.67 at%, Ni is 33.21 at%, Cu is 8.9 at%, and O is It was 8.9 at%.

The measurement of electron energy loss spectroscopy (also referred to as Electron Energy-Loss Spectroscopy, EELS) of the porous alloy compound 1 of the present invention will be described.
15A is a STEM image of a EELS measurement location, FIG. 15B is a low energy EELS spectrum, and FIG. 15C is a high energy EELS spectrum. 5B and 5C, the horizontal axis represents energy loss (keV), and the vertical axis represents electron beam intensity (arbitrary scale). As shown in FIG. 15A, the EELS measurement was performed at the locations indicated by A and B. Table 2 shows the compositions of A and B calculated from the EELS spectra shown in FIGS.

From the above measurement, the weight ratio of the oxidation-hydroxide 3 of the electrode made of the porous alloy compound 1 was calculated to be about 9.16%. The density of the electrode of the porous alloy compound 1 of the present invention is 4.6 gcm ⁻³ . From this, the mass fraction of the oxidation-hydroxide 3 of the porous alloy compound 1 of the present invention was determined to be about 0.42 gcm ⁻³ .

Thereby, the specific capacity of the electric double layer capacitor 10 using the porous alloy compound 1 of the present invention is 1493 Fg ^{−1 as} shown in FIG. 13. This specific capacity is a value comparable to 1300-1500 Fg ⁻¹ , which is the theoretical value of RuO ₂ , which is two important materials in actual application, and about 1370 Fg ^{−1 of} MnO ₂ (see Patent Document 14).

  Table 3 summarizes the specific capacitance reported in the electric double layer capacitor 10 of the present invention and non-patent literature.

FIG. 16 is a diagram showing a lagone plot of the electric double layer capacitor 10 of the first example. In the figure, the horizontal axis represents power density (W / cm ³ ), and the vertical axis represents energy density (Wh / cm ³ ).
The electric double layer capacitor 10 using the porous alloy compound 1 of the present invention has a large potential window, and the energy density of the electric double layer capacitor 10 is a very large value of 51 mWh / cm ³ and 18 W A high power density of / cm ³ is obtained. This energy density is twice or more larger than the best value (see Non-Patent Documents 2 and 10) obtained with conventional aqueous electrolytes and non-aqueous electrolytes.

  Although the metal skeleton 2 of the polarizable electrode 2 using the porous alloy compound 1 of the present invention is much heavier than the carbon material or the oxide-hydroxide 3, the mass energy density of the electric double layer capacitor 10 is high. Due to the high load of oxide-hydroxide 3 of capacity, it is about 14 Wh / kg. The mass energy density of the electric double layer capacitor 10 of the present invention is comparable to the best value reported so far (see Non-Patent Documents 2, 4, and 10).

  In the electric double layer capacitor 10 using the conventional carbon or other pseudo electric capacitive material, the collector electrode 15 and the binder are necessary to form the polarizable electrode 2.

  Compared with the conventional electric double layer capacitor, in the electric double layer capacitor 10 using the porous alloy compound 1 of the present invention, the metal skeleton 2 of the polarizable electrode 2 can be self-supported by the highly conductive metal skeleton 2. As a result, the metal skeleton 2 serves as a reinforcement having an active oxide-hydroxide 3 skeleton, and also acts as a collecting electrode 15 for flowing a current through the electric double layer capacitor 10.

  Therefore, the mass energy density of the electric double layer capacitor 10 of the present invention is about 10 Wh / kg even when the weight as the element is taken into consideration, which is about twice as large as that of the electric double layer capacitor 10 using carbon ( Non-patent document 2).

(Measurement of impedance)
Electrochemical impedance spectroscopy of the electric double layer capacitor 10 of the present invention was measured at a frequency of 0.1 Hz to 100 kHz and an AC voltage amplitude of 50 mV.
FIG. 17 is a diagram showing a Nyquist plot of the electrochemical impedance of the electric double layer capacitor 10. The horizontal axis in the figure is the real axis (Ω), and the vertical axis is the negative imaginary axis (Ω). The inset in the figure is a Nyquist plot on the high frequency side.
As shown in FIG. 17, on the high frequency side, the impedance of the electric double layer capacitor 10 is a semicircle with a small resistance (Rct). This indicates that the resistance due to charge transfer at the interface between the electrode and the electrolyte is small. This small resistance comes from the hierarchical porous structure of the electrode. As a result, a large contact area with the electrolyte and a short charge transfer between the electrolyte and the collector electrode 15 made of the metal skeleton 2 can be realized.

  At low frequencies, Warburg impedance with a slope close to 45 degrees is observed. Warburg impedance indicates that the semi-infinite diffusion of cations at the electrode is highly efficient. The inclination smaller than 45 degrees indicates that the electrochemical property of the electrode of the electric double layer capacitor 10 using the porous alloy compound 1 of the present invention is controlled by the diffusion resistance of the electrolyte. This is due to the fact that the porous pores of the porous alloy compound 1 are 1 nm or less, that is, very small, as shown in the STEM image of FIG. 5 and the measurement by the BET method. The low intrinsic resistance is intimately related to the valence of the composite oxide-hydroxide 3 mixed with metal cations and the reinforcement of the metal skeleton 2.

(Cycle characteristics of electric double layer capacitor)
In addition to the high energy density of the electric double layer capacitor 10, long-term cycle characteristics are also important factors for practical applications.
The cycle characteristics of the electric double layer capacitor 10 of the present invention were carried out by a charge / discharge test with a current density as low as ³ A / cm ³ .
FIG. 18 is a diagram showing cycle characteristics of the electric double layer capacitor 10. In the figure, the horizontal axis represents the cycle number, and the vertical axis represents the capacity retention rate (%). As is clear from FIG. 18, almost no deterioration in capacity retention during the cycle was observed. The capacity retention after 2300 cycles was about 99.7%. Thereby, it turns out that the stability of the electric double layer capacitor 10 by the porous alloy compound 1 of this invention is good.

(Observation of cycle characteristics of electric double layer capacitor)
The microstructure after 2300 cycle tests was measured by STEM, XRD, ELLS and XPS. No degradation of the oxide-hydroxide 3 was observed. As a result, it was confirmed that the electric double layer capacitor 10 was electrochemically and mechanically stable with a high potential window of 1.8 V in the aqueous electrolyte.

  Many pseudo-electrical capacitative materials have theoretically high specific capacities, but the realization of high energy applications is often poor conductivity, narrow potential windows, electrochemical and mechanical This is limited by low stability (see, for example, Non-Patent Documents 15 and 16).

Next, a comparative example of the porous alloy compound 1 of the present invention will be described. The characteristics of the porous alloy compound of the comparative example shown below were examined by the same measurement method as in Example 1.
(Comparative Example 1)
An electrode made of NiMn binary alloy oxide-hydroxide 3 was used as Comparative Example 1. A Ni ₃₀ Mn ₇₀ alloy ribbon was prepared in the same manner as in Example 1. This alloy ribbon was demetalized using a 1M (mol) (NH ₄ ) ₂ SO ₄ solution to desorb unstable Mn, and a binary alloy composed of nanoporous Ni ₈₆ Mn ₁₄ was obtained. . The size of the nanoporous pores is 6-7 nm, which is larger than that in Example 1. Due to the polarization of the binary alloy, the binary alloy composed of nanoporous Ni ₈₆ Mn ₁₄ is oxidized, and the nanoporous channel is filled with the oxidation-hydroxide of NiMn.

  FIG. 19 is a diagram showing a scanning transmission microscope (STEM) image after polarization of the porous alloy compound of Comparative Example 1, and the inset is a limited field electron diffraction (SAED) image. It can be seen from the SAED pattern shown in FIG. 19 that the polarized NiMn alloy has the same structure as the NiMnCu alloy of Example 1.

  From the XPS measurement, it was confirmed that the Ni-Mn oxide-hydroxide contained divalent and tetravalent Mn ions and divalent Ni ions.

FIG. 20 shows the CV curve of the porous alloy compound of Comparative Example 1. The size of the potential window is 1V. In the figure, the horizontal axis represents voltage (V) and the vertical axis represents current (A). As shown in FIG. 20, a set of redox peaks in the vicinity of 0.4 V (oxidation) and 0.2 V (oxidation) are observed. These peaks are related to the reversible reaction between Ni ²⁺ and Ni ³⁺ . In the CV curve, a rectangular region clearly exists when the potential window is in the range of −0.4V to 0.1V. This rectangular region is related to the capacitive behavior of Mn ions.

Thus, both the Ni and Mn cations contribute to the capacity characteristics of the porous alloy compound of Comparative Example 1. This characteristic is the same as the capacity characteristic of the porous alloy compound made of MnO ₂ —NiO.

In Comparative Example 1, an irreversible Faraday process was observed when the potential was more negative than -0.2V. This phenomenon is similar to the reported behavior of MnO ₂ .

After several tens of cycles, the rectangular area in the capacitive characteristics gradually disappeared and the electrolyte color changed to yellow. The unstable capacity characteristics of the binary oxide-hydroxide are the same as in the case of V ₂ O ₅ .

  According to XPS analysis, the Mn concentration of the porous alloy compound of Comparative Example 1 rapidly decreased with the number of cycles. This is presumably due to dissolution of Mn ions on the cathode potential side. Thus, the porous alloy compound of Comparative Example 1 is unstable in a large potential window.

FIG. 21 is a diagram showing CV curves at different sweep rates when the potential window is −0.4 V to 0.5 V, in which the horizontal axis represents voltage (V) and the vertical axis represents current (A). As is clear from this figure, the redox reaction is the same as the reaction between Ni (OH) ₂ (see Non-Patent Document 8) and NiO.

(Comparative Example 2)
An electrode made of an oxide-hydroxide of a CuMn binary alloy was used as Comparative Example 2. A Cu ₃₀ Mn ₇₀ alloy ribbon made of a CuMn binary alloy was produced in the same manner as in Example 1. This alloy ribbon was demetalized using a 1M (mol) (NH ₄ ) ₂ SO ₄ solution to desorb unstable Mn to obtain a binary alloy composed of nanoporous CuMn. The size of the nanoporous pores was 20-30 nm

  FIG. 22 shows an SEM image of the de-alloyed CuMn binary alloy of Comparative Example 2. As is clear from FIG. 22, the size of the dealloyed CuMn nanoporous pores is larger than that of the example.

As in Example 1, the dealloyed binary alloy of CuMn was electrochemically polarized.
23 shows an SEM image of the CuMn binary alloy after polarization in Comparative Example 2. FIG. As is apparent from FIG. 23, after polarization, the CuMn binary alloy was completely oxidized.

24 is a diagram showing an X-ray diffraction (XRD) of the porous alloy compound of Comparative Example 2. FIG. The horizontal axis of the figure is 2θ (degrees), and the vertical axis is the X-ray diffraction intensity (arbitrary scale). As is apparent from FIG. 24, it can be seen that the porous alloy compound of Comparative Example 2 is made of CuO, Cu ₂ O, Cu ₄ O ₃ or the like.

  Since the oxide of Cu is not formed as a protective film for the skeleton in nanoporous copper in 1 M KOH electrolyte, the stability of capacity and cycle characteristics is dramatically lost even in a narrow potential window of 1 V or less. Is called.

  Compared with Comparative Example 1 and Comparative Example 2 and the conventional pseudo-electric capacitive material, the porous alloy compound 1 of the present invention has a valence in which the oxidation-hydroxide 3 is mixed with metal cations, and is oxidized. -The hydroxide 3 is supported by a highly conductive metal skeleton 2. Thus, the porous alloy compound 1 of the present invention has high electrical conductivity for fully utilizing the high specific capacity of the oxide-hydroxide 3 having a composite composition. The high specific capacity is due to multiple redox reactions at different potentials due to the effective utilization of multiple cations in the material. Combined with the high potential window of 1.8 V, the electric double layer capacitor 10 based on the oxide-hydroxide 3 can maintain a high power density and provide a high energy density.

  Like the oxide, the oxide-hydroxide 3 is fragile and fragile in the charge / discharge process, but the electrode using the oxide-hydroxide 3 of the present invention has an unusually high cycle retention characteristic. Yes. This cycle retention characteristic is because the fragile oxide-hydroxide 3 is mechanically accommodated in a channel composed of pores in the nanometer (nm) order of the metal skeleton 2 which is another component.

  The rugged electrode made of the porous alloy compound 1 of the present invention produced by electrochemical dealloying and polarization of an inexpensive transition metal alloy is an industrial level for a wide range of high energy and high power applications. Ready to scale up. The dealloying and polarization used in the present invention is compatible with the electrochemical process at the industrial level and, more importantly, does not contain expensive precious metals or chemicals.

  Electrodes based on oxide-hydroxide 3 that do not need to be supported can be made from 5 to 6 μm thick, that is, from several μm to 100 μm, with one side dimension from mm to 10 cm. It can be used for the double layer capacitor 10.

  The low cost and mass productivity of the materials and processes, and the excellent capacity characteristics due to the oxidation-hydroxide 3 of the present invention, which has not been obtained so far, show promise for practical electric double layer capacitor 10 applications. .

  The electric double layer capacitor 10 of the present invention is also effective for next-generation energy storage.

Although the present invention has been described in detail in the above embodiments with the metal M ₁ as Mn and the metal M ₂ as Ni and Cu as the best mode, Mn is replaced with V because the oxide has pseudo-electric capacity. However, Ni and Cu may be replaced with other transition metals because they have high electrical conductivity. Even with these materials, a porous alloy compound can be produced by the same production method as in the above example. Like the above example, the porous alloy compound has a higher potential window than the conventional electrode constituent material. Expected to have. Therefore, the present invention is not limited to the embodiments, and various modifications are possible within the scope of the claims, and it goes without saying that these are also included in the scope of the present invention.

1: porous alloy compound 2: metal skeleton 3: oxidation-hydroxide 4: alloy 5: porous alloy 10: electric double layer capacitor 12: polarizable electrode 12a: first polarizable electrode 12b: second Polarization electrode 13: Separator 14: Electrolytic solution 15: Collector

Claims (10)

Under following formula (1):
^{_{(Ni II a Cu I b Cu}} II c Mn II d Mn IV e) O f (OH) g (H 2 O) h (1)
(In the formula (1), a, b, c, d, e, f, g and h, respectively, a + b + c + d + e + f + g + h = 100 than zero or a positive number der meet, d + e> a, a d + e> b + c, 20 ≦ a + b + c + d + e ≦ 40, 20 <f <40, 20 <g <40 )
A porous alloy compound represented by : The porous alloy compound according to claim 1 , wherein an average pore diameter of the porous alloy compound is 0.1 to 10 nm. The porous alloy compound according to claim 1 or 2 , wherein the X-ray diffraction pattern has peaks close to Cu, Ni and Mn, and 2θ = 36.5 ° and 2θ = 61.6 °. A manufacturing method of a porous alloy compound according to any one of claims 1~ 3, Mn, Ni, step 1 to produce a porous alloy and de-alloying composed alloy Cu,
Step 2 of polarizing the porous alloy with an alkaline solution to obtain a porous alloy compound;
A method for producing a porous alloy compound having The method for producing a porous alloy compound according to claim 4, wherein the porous alloy compound is a thin film. The porous alloy has the following formula (2):
_{Mn x -Ni y -Cu z (2} )
(Equation (2), x, y and z, x + y + z = 100 , x ≦ y, Ri number der positive satisfying x ≦ z, is 10 ≦ x ≦ 30)
The manufacturing method of the porous alloy compound of Claim 4 or 5 which has the structure represented by these. In the step 1, the alloy is immersed in a solution of at least one compound selected from the group consisting of ammonium sulfate ((NH ₄ ) ₂ SO ₄ ), NaCl, KCl, Na ₂ SO ₄ and K ₂ SO _4. The method for producing a porous alloy compound according to claim 4, wherein a porous alloy is obtained by dealloying. The method for producing a porous alloy compound according to claim 4, wherein the alkaline solution is any one of KOH, NaOH, and LiOH. Electric double layer capacitor using a porous alloy compound of any one of claims 1 to 3 as a polarizable electrode. The electric double layer capacitor according to claim 9 , wherein the porous alloy compound is used as a collector electrode.