JP5116946B2 - Electrochemical cell suitable for use in electronic devices - Google Patents

Description

The present invention relates to a novel electrochemical cell, which can be a battery and / or a supercapacitor, suitable for use in portable electronic devices and other electronic devices. In particular, the present invention relates to an electrochemical cell having at least a positive electrode formed of a mesoporous material having a periodic array of substantially uniform size pores having a cross section of about 10 ⁻⁸ to 10 ⁻⁹ m.

  Note that the term “battery” is used herein in the general sense of a device that converts the chemical energy contained in its active ingredients directly into electrical energy by a redox (oxidation-reduction) reaction. Should. The basic unit of the battery is an electrochemical cell, which includes at least a positive electrode, a negative electrode, and an electrolyte, all of which are stored in a casing. Other components such as separators may be included as is well known in the art. The battery can consist of one or more such cells.

  Many portable electronic devices require power to be available at a relatively low level steady flow interspersed with much higher power drain spikes or surges. Most conventional batteries cannot meet these requirements and can therefore be supplemented with a capacitor or supercapacitor that stores power when not needed by the device and releases power when needed. Examples of devices having this type of power requirement include notebook computers, cell phones, PDAs (personal digital assistants or microcomputers), defibrillators, and the like. However, in such portable devices, portability is important and portability is a function of both weight and size. Any further apparatus in the device necessarily increases both of these, reducing the portability of the device and is therefore less desirable.

  Consequently, the requirement for any electrochemical cell to function in such a portable device is that it must have both high power density and high energy density. Previously, at reasonable cost, it was only possible to achieve one or the other of these densities, but not both.

  We can now apply, for example, the mesoporous film technology disclosed in EP 993512 or US Pat. No. 6,203,925 to the production of one or both electrodes of an electrochemical cell. It has now been discovered that electrochemical cells that can function as the resulting battery, capacitor or both can be designed to have both high power density and high energy density.

Accordingly, the present invention is a portable electronic device including an electrochemical cell having a positive electrode, a negative electrode and an electrolyte, wherein the active material of the positive electrode has a substantially uniform size with a cross section of 10 ⁻⁸ to 10 ⁻⁹ m. and platinum has a periodic arrangement of pores, nickel, consists mesoporous material formed of a material selected from nickel hydroxide (Ni (OH) ₂₎ or nickel oxyhydroxide (NiOOH), the negative electrode active material, to provide a portable electronic device characterized by comprising a mesoporous material selected palladium, iron or carbon.

  The present invention also provides a portable electronic device including such an electrochemical cell.

  Furthermore, this invention provides the battery for motor vehicles containing the some electrochemical cell of this invention.

The electrochemical cell of the present invention can be configured to function as a battery, as a supercapacitor, or as a combined battery / supercapacitor. As shown in the schematic diagram of FIG. 1, for example, a supercapacitor having a mesoporous positive electrode and a negative electrode has a proton reciprocation mechanism between a mesoporous positive electrode of, for example, Ni (OH) ₂ and a hydrogen absorbing mesoporous negative electrode of, for example, palladium. It works by. Mechanism is similar to the operation mechanism in Ni-MH battery, in this case, the palladium is replaced by another of the hydrogen-absorbing material, such as LaNi _5.

  Examples of portable electronic devices that can contain the electrochemical cells of the present invention include portable computers including so-called notebook computers, desktop replacement computers, ultraportable computers, etc. Small version is particularly valuable), music based on mobile phones, cordless (landline) phones, PDAs, portable hard disk drives, CD players, cassette players, mini-disc players, and MP3 and similar software Various types of music players, including other digital recording music players including players, portable TVs, portable DVD players, portable radios, PDAs / cell phones, telephone / music players, Hybrid devices such as disk storage / music player (i.e., formerly devices perform more than one function was separately) and, like a medical devices such as defibrillators.

  The electrochemical cell of the present invention can also be used in automobile batteries.

  All of the above devices require a steady supply of relatively low levels of power interspersed with periodic demands for much higher power at essentially random intervals. They are therefore particularly suitable for use with the electrochemical cells of the present invention. The details of the design and construction of these devices are well known and do not form part of the present invention other than incorporating an electrochemical cell according to the present invention.

At least the positive electrode and the cathode of the electrochemical cell of the present invention are formed of a mesoporous material. The material is preferably a metal, metal oxide, metal hydroxide, metal oxyhydroxide, or a combination of any two or more of these. Examples of such metals include nickel and transition metal alloys, nickel alloys including nickel / cobalt alloys and iron / nickel alloys, cobalt, platinum, palladium, and ruthenium. Examples of such oxides, hydroxides and oxyhydroxides include gold oxide, palladium oxide, nickel oxide (NiO), nickel hydroxide (Ni (OH) ₂ ), nickel oxyhydroxide (NiOOH), And ruthenium oxide. Of these, nickel and its oxides and hydroxides are most preferred.

  As is well known in the art, some of these materials require “conditioning” before use. This can be accomplished by subjecting the cell to several charge and discharge cycles, as is conventional in the art. A typical material that requires such conditioning is nickel, and conditioning can result in an oxide surface layer.

There is no restriction | limiting with respect to the property of the material used in order to manufacture the negative electrode of the electrochemical cell of this invention, and an anode, Arbitrary materials can be used in consideration of the chemical property of the cell which should be manufactured. Examples of suitable materials are carbon, cadmium, iron, palladium / nickel alloy, iron / titanium alloy, palladium, or mixed metal hydrides such as LaNi ₅ H _x . These materials are preferably porous and more preferably mesoporous. Of these, preferred materials are carbon and palladium. However, mesoporous palladium is not a preferred negative electrode material for low cost applications due to its high cost.

  Preferred combinations of anode and cathode are nickel / palladium, nickel / carbon, nickel / iron and nickel / cadmium, of which nickel / carbon is most preferred. When referring to nickel, its oxides and hydroxides are also included.

In particular, the mesoporous structure of the positive electrode includes nickel and oxidation, hydroxide or nickel oxyhydroxide selected from NiO, Ni (OH) ₂ and NiOOH, where the oxide or nickel hydroxide is a surface layer on the nickel. And at least extending over the surface of the pores, the negative electrode preferably contains nanoparticulate carbon.

Thus, preferably, the positive electrode and the negative electrode each include a mesoporous structure having a periodic array of substantially uniform sized pores with a cross-section of about 10 ⁻⁸ to 10 ⁻⁹ m. The positive electrode and negative electrode (if the negative electrode is also mesoporous) consist of defined mesoporous structure (s) or substantially consist of defined mesoporous structure (s).

  “Mesoporous structure”, “mesoporous material” and “mesoporous film”, as referred to herein, are manufactured by a liquid crystal template process, resulting in a monolithic nature, a defined topology and substantially Each means a structure, material and film containing a regular array of pores with a uniform pore size (diameter) over a long distance. Thus, mesoporous structures, materials and films can also be described as being nanostructured or having a nanoarchitecture.

  Thus, mesoporous materials used in accordance with the present invention are traditionally referred to as “nanomaterials” composed of materials with low crystallization, as well as composite materials with discrete nano-sized solid particles, eg, nanoparticle aggregates. Differentiated from things.

  Compared to nanomaterials, the advantage of using mesoporous materials is that the transport of electrons in the mesoporous material does not encounter grain boundary resistance, provides excellent electron conductivity and eliminates the power loss associated with this phenomenon That is. Furthermore, the regular porosity of the mesoporous material used herein provides a uniform diameter non-meandering flow path that is continuous and relatively straight, facilitating fast and unimpeded migration of electrolyte species. In contrast, conventional nanoparticle systems have a messy porosity, which has voids of various cross-sections interconnected by spaces between the narrower voids. In such cases, substances that move through the pore structure will encounter rather serpentine passages, resulting in slower reaction rates.

  The mesoporous material is preferably in the form of a film having a substantially constant thickness. Preferably, the thickness of the mesoporous film is in the range of 0.5-5 micrometers.

  Preferably, the mesoporous material has a pore diameter in the range of about 1-10 nanometers, more preferably in the range of 2.0-8.0 nm.

The mesoporous material is 1 × 10 ¹⁰ to 1 × 10 ¹⁴ pieces / cm ² , preferably 4 × 10 ^{11 to} 3 × 10 ¹³ pieces / cm ² , more preferably 1 × 10 ¹² to 1 × 10 ¹³ pieces / cm ^2. A pore number density in the range of

  The mesoporous material has pores of substantially uniform size. “Substantially uniform” means that at least 75%, for example 80% -95% of the pores have a pore diameter within 30%, preferably within 10%, most preferably within 5% of the average pore diameter. It means having. More preferably, at least 85%, for example 90% to 95% of the pores have a pore diameter within 30%, preferably within 10%, most preferably within 5% of the average pore diameter.

  The pores are preferably cylindrical in cross section and preferably exist or extend throughout the mesoporous material.

  Mesoporous structures are defined recognizable topologies or architectures (eg cubic, layered, oblique, centred rectangular, body-centered orthorhombic, body-centered tetragonal, rhombohedral, hexagonal) ) Having a periodic arrangement of pores. Preferably, the mesoporous structure has a hexagonal periodic pore arrangement, wherein the electrode has a uniform diameter and is continuous through the thickness of the electrode and oriented in a hexagonal system. Perforated by a large number of pores.

  Where the pore arrangement is preferably hexagonal, the pore arrangement is preferably in the range of 3-15 nm, more preferably in the range of 5-9 nm, corresponding to the center-to-center spacing of the pores. It has regular pore periodicity.

  Furthermore, the mesoporous structure having this regular periodicity and a substantially uniform pore size should extend over the electrode portion at least about 10 times, preferably at least about 100 times the average pore size. Preferably, the electrode consists of the defined structure (s) or substantially consists of the defined structure (s).

  These pore topologies are not limited to ideal mathematical topologies, but on the condition that there is a recognizable architecture or topological order in the spatial arrangement of pores in the film. It will be appreciated that strain or other changes may be included. Thus, as used herein, the term “hexagonal” refers not only to materials that exhibit mathematically perfect hexagonal symmetry within the limits of measurement, but also to most channels at substantially the same distance. Also included are materials that have a significantly observable deviation from the ideal state, provided that they are surrounded by an average of six nearest adjacent channels. Similarly, the term “cubic” as used herein includes not only materials that exhibit mathematically complete symmetry belonging to the cubic space group within the limits of measurement, but also most channels 2 Also included are materials that have a significantly observable deviation from the ideal state, provided that they connect to six other channels.

  The electrolyte in the cell is preferably an aqueous electrolyte, for example, an aqueous alkaline electrolyte such as potassium hydroxide water.

In a preferred embodiment, the mesoporous structure of the positive electrode comprises nickel and an oxidation, hydroxide or nickel oxyhydroxide selected from NiO, Ni (OH) ₂ and NiOOH, wherein said oxidation, hydroxide or nickel oxyhydroxide Forms a surface layer on the nickel and extends at least on the surface of the pores, and the negative electrode has a mesoporous structure of carbon or palladium. When filled with electrolyte, the positive electrode represents a three-phase composite composed of interconnected Ni current collector bases coated with Ni (OH) ₂ active material in contact with the electrolyte. Advantageously, the hydration structure of the mesoporous Ni cathode is retained so that both surface and bulk processes can contribute to the charge capacity of the electrode. Due to the nanoscale structure of the electrode, all three phases are in intimate contact with each other, or within about 1-2 nm, and the total surface area of the “phase boundary” is very large. Thus, a high energy density can be achieved and the small proton diffusion distance allows the cell to exhibit a very high power density.

  The mesoporous material used as the positive electrode of the electrochemical cell of the present invention and optionally as the negative electrode is prepared by a liquid crystal template method and is preferably deposited as a film on a substrate by electrochemical deposition from a lyotropic liquid crystal phase. They can also be prepared by electroless deposition such as chemical reduction from a lyotropic liquid crystal phase.

  Suitable substrates include gold, copper, silver, aluminum, nickel, rhodium or cobalt, or any of these metals or alloys containing phosphorus. The substrate may be microporous with pores preferably in the size range of 1-20 micrometers, if desired. The substrate preferably has a thickness in the range of 2-50 micrometers. The substrate is preferably the above-mentioned substrate other than gold on which a gold layer is formed by vapor deposition.

  Suitable methods for depositing mesoporous material as a film on a substrate by electrochemical deposition and chemical means are known in the art. For example, a suitable electrochemical deposition method is disclosed in European Patent No. 993,512 and Nelson et al. “Mesoporous Nickel / Nickel Oxide Electrodes for High Power Applications”. J. New Mat. Electrochem. Systems, 5, 63-65 (2002) and Nelson et al., “Mesoporous Nickel / Nickel Oxide / a Nanoarchitectured Electrode”, Chem. Mater. , 2002, 14, 524-529. A suitable chemical reduction method is disclosed in US Pat. No. 6,203,925.

Preferably, the mesoporous material is formed by electrochemical deposition from the lyotropic liquid crystal phase. According to a general method, the template is formed into a desired liquid crystal phase such as a hexagonal phase by self-assembly from a certain long chain surfactant and water. Suitable surfactants include octaethylene glycol monohexadecyl ether (C ₁₆ EO ₈ ), which has a long hydrophobic hydrocarbon tail attached to the head group of the hydrophilic oligoether. Others include polydisperse surfactant Brij® 56 (C ₁₆ EO _n , where n is about 10), Brij® 78 (C ₁₆ EO _n , where n is about 20 And Pluronic 123, each available from Aldrich. At high (> 30%) aqueous solution concentrations, depending on the concentration and temperature used, the aqueous solution can be stabilized in the desired lyotropic liquid crystal phase consisting of separated hydrophilic and hydrophobic domains, for example the hexagonal phase. And the aqueous solution is bound to the hydrophilic domain. Dissolved inorganic salts, such as nickel acetate, can also be constrained to the hydrophilic domain and electroreduced with an electrode immersed in the solution to form a solid intermediate phase of, for example, nickel metal. This is a direct cast of an aqueous domain phase structure. Subsequent removal of the surfactant by washing in a suitable solvent leaves a large number of regularly periodic pores in the electroreduced solid, and the pore arrangement is selected from the lyotropic liquid crystal Determined by phase. Topology, size, periodicity, and other pore properties vary with appropriate selection of surfactants, solvents, metal salts, hydrophobic additives, concentration, temperature and deposition conditions, as known in the art Can be made.

  As described above, the mesoporous material from which the mesoporous electrode is manufactured is preferably formed on the substrate by electrodeposition or chemical deposition. The mesoporous material is preferably used as an electrode on the substrate since it may lack adequate mechanical strength, and for convenience this is preferably the same substrate used in its fabrication.

  The invention is further illustrated by the following non-limiting examples with reference to the drawings.

  The invention is further illustrated by the following non-limiting examples.

[Example 1]
[Electroplating of platinum from hexagonal liquid crystal phase]
3 grams of octaethylene glycol monohexadecyl ether (C ₁₆ EO ₈ ) surfactant was added to 2.0 grams of water and 2.0 grams of hexachloroplatinic acid hydrate. The mixture was heated and shaken vigorously until a uniform mixture was obtained. By stepping the potential from +0.6 volts for the standard calomel electrode to -0.1 volts for the standard calomel electrode until a 2 millicoulomb reduction charge passes, 0.000314 square centimeters. Electrodeposition from this mixture was performed on a polished gold electrode at a temperature of 25 ° C to 85 ° C. The surfactant was removed by rinsing with distilled water. A film having a metal structure is obtained, which is a hexagonal crystal of pores having an inner diameter of 25 mm (± 1.5 mm) separated by a metal wall of width 25 mm (± 2 mm) in an experiment by transmission electron microscopy. It was found to have a system configuration.

[Example 2]
[Electroplating of platinum from hexagonal liquid crystal phase]
Instead of C ₁₆ EO ₈ , the process of Example 1 was carried out using a shorter chain length surfactant, C ₁₂ EO ₈ . The pore diameter determined by TEM was found to be 17.5 mm (± 2 mm).

[Example 3]
[Electroplating of platinum from hexagonal liquid crystal phase]
The process of Example 1 was repeated using a quaternary mixture containing a 2: 1 molar ratio of C ₁₆ EO ₈ and n-heptane. The pore diameter was found to be 35 mm (± 1.5 mm) as determined by TEM.

[Example 4]
[Electroplating of platinum from cubic liquid crystal phase]
From a 27 wt% hexachloroplatinic acid aqueous solution (33 wt% with respect to water) and 73 wt% octaethylene glycol monohexadecyl ether (C ₁₆ EO ₈ ), the cubic phase of normal topology (indicating the Ia3d space group) A mixture was prepared. Electrodeposition on a polished gold electrode was performed using a potentiostat at a temperature of 35 ° C. to 42 ° C. using a platinum mesh counter electrode. The cell potential difference was stepped from + 0.6V for the standard calomel electrode to -0.1V for the standard calomel electrode until a 0.8 millicoulomb charge passed. After deposition, the film was rinsed with a large amount of deionized water to remove the surfactant. The washed nanostructured precipitate was uniform and glossy in appearance. Transmission electron microscopy studies have revealed a very porous structure consisting of a three-dimensional periodic network of cylindrical holes with an inner diameter of 25 mm.

[Example 5]
[Electrodeposition of nickel from hexagonal liquid crystal phase]
From an aqueous solution of 50% by weight of 0.2M nickel (II) sulfate and 0.58M boric acid and 50% by weight of octaethylene glycol monohexadecyl ether (C ₁₆ EO ₈ ), a hexagonal phase of normal topology is obtained. A mixture having was prepared. Electrodeposition on a polished gold electrode was performed using a potentiostat at 25 ° C. using a platinum mesh counter electrode. The cell potential difference was stepped to -1.0 V against a saturated calomel electrode until a charge of 1 coulomb per square centimeter passed. After deposition, the film was rinsed with a large amount of deionized water to remove the surfactant. The washed nanostructured precipitate was uniform and glossy in appearance. A small-angle X-ray diffraction study of electrodeposited tin reveals a periodicity of a 58 mm lattice, and a transmission electron microscopy study shows a cylindrical shape with an inner diameter of 34 mm separated by a 28 mm thick nickel wall. A very porous structure consisting of pores was revealed.

[Example 6]
From a hexagonal liquid crystal phase consisting of 2.0 g H ₂ O, 3.0 g C ₁₆ EO ₈ , and 2.0 g hexachloroplatinic acid, stepped from −0.1 V (+0.6 V to SCE). The deposition on the metal plate electrode was carried out at 25 ° C. at the deposition potential of (ii). Thickness data was obtained by inspecting the crushed samples using scanning electron microscopy. The results are shown in Table 1 below.

[Example 7]
A nanostructured platinum film was deposited from a hexagonal liquid crystal phase consisting of 2.0 g H ₂ O, 3.0 g C ₁₆ EO ₈ , and 2.0 g hexachloroplatinic acid. Deposition was performed on a gold disk electrode with a diameter of 0.2 mm at a deposition potential of −0.1 V (stepped from +0.6 V) relative to SCE. The charge passed was 6.37 Ccm ⁻² . Data were obtained from cyclic voltammetry in 2M sulfuric acid at a potential limit of -0.2V to + 1.2V relative to SCE. The roughness coefficient is defined as the surface area determined from electrochemical experiments divided by the geometric surface area of the electrode. The results are shown in Table 2 below.

[Example 8]
A nanostructured platinum film was deposited from a hexagonal liquid crystal phase consisting of 2.0 g H ₂ O, 3.0 g C ₁₆ EO ₈ , and 2.0 g hexachloroplatinic acid. Deposition was performed on a gold disk electrode with a diameter of 0.2 mm at the indicated deposition potential (stepped from +0.6 V). The charge passed was 6.37 Ccm ⁻² . Data were obtained from cyclic voltammetry in 2M sulfuric acid at a potential limit of -0.2V to + 1.2V relative to SCE. The results are shown in Table 3 below.

[Consideration of Examples 1 to 8]
The data of Examples 1-3 show how the pore diameter can be controlled by changing the chain length of the surfactant or by further adding a hydrophobic hydrocarbon additive. In particular, the comparison between Example 1 and Example 2 demonstrates that the pore size can be reduced by using a surfactant with a shorter chain length, whereas the comparison between Example 1 and Example 3 , Indicating that the pore size can be increased by adding a hydrocarbon additive to the precipitation mixture.

  Example 6 demonstrates how the thickness of the deposited film can be controlled by changing the charge passed during electrodeposition.

  Examples 7 and 8 show how the temperature and applied potential during electrodeposition affects the film surface area and double layer capacitance. As indicated by the roughness coefficient value, increasing the deposition temperature increases both the surface area of the film and the double layer capacitance. At the same time, the deposition potential can be selected to control the surface area and capacitance of the deposited film.

[Example 9]
[Preparation of mesoporous nickel electrode and mesoporous palladium electrode]
[(I) Preparation of gold substrate]
A mesoporous nickel electrode comprising a gold disk (diameter 200 μm or 1 mm) encapsulated in an epoxy insulator and a thin film gold electrode (approximately 1 cm ² ) produced by vapor deposition of gold on a chromium-coated microscope glass slide And the palladium electrode was then prepared as follows for deposition.

Polished first on a micro cloth embedded with 25 μm, 1 μm and 0.3 μm alumina (obtained from Buehler), then saturated mercury sulfate in ₂ M H ₂ SO ₄ solution at 200 mVs ⁻¹ for 5 minutes The gold disk electrode was cleaned by cycling the electrode at -0.6V to 1.4V relative to a reference electrode (SMSE). In each cycle, a single layer of gold oxide was formed and subsequently removed from the electrode surface.

  The deposited gold electrode was cleaned in an isopropanol ultrasonic bath for 60 minutes prior to deposition, then rinsed with deionized water and dried under ambient conditions.

[(Ii) Electrodeposition of nickel from hexagonal liquid crystal phase]
35 wt% 0.2 M nickel acetate (II), 0.5 M sodium acetate and 0.2 M boric acid in water, and 65 wt% Brij® 56 nonionic surfactant (C ₁₆ EO _n, from where n is obtained from about 10, Aldrich), a mixture having a hexagonal regular topology (H _I) phase was prepared, Chem such Nelson. Mater., 2002, 14 , to 524-529 In accordance with the disclosed method, electrodeposition on a polished gold substrate was performed using a potentiostat at 25 ° C. using a platinum mesh counter electrode. After deposition, the film was washed in a large amount of isopropanol for 24 hours to remove the surfactant. A mesoporous nickel film about 1 micrometer thick with hexagonal pore arrangement was obtained.

[(Iii) Electrodeposition of palladium from hexagonal liquid crystal phase]
35 wt% 0.5 M ammonium tetrachloropalladate (obtained from Premion, Alfa Aesar) and 65 wt% Brij® 56 non-ionic surfactant (C ₁₆ EO _n , where n is from about 10, Aldrich available), and the mixture having a regular hexagonal topology (H _I) phase was prepared. In 25 ° C., the presence of H _I crystal phase of palladium precipitation template solution, was confirmed using polarizing microscopy. According to the electrodeposition method disclosed in Phys. Chem. Chem. Phys., 2002, 4, 3835-3842 of Bartlett et al. Electrodeposition on the gold substrate was performed using a potentiostat. After deposition, the film was washed in a large amount of isopropanol for 24 hours to remove the surfactant. A mesoporous palladium film about 1 micrometer thick with hexagonal pore arrays was obtained.

[(Iv) Operation of electrodeposited mesoporous Ni and Pd electrodes]
Prior to assembly of the supercapacitor, the deposited mesoporous electrodes prepared in (ii) and (iii) above were individually actuated by cyclic voltammetry. This was performed in a three-electrode cell containing 6M KOH solution. The cell consisted of a Pyrex water jacketed cell connected to a water bath with a Grant ZD thermostat, a mercury / mercury oxide (6M KOH) reference electrode (Hg / HgO), and a large area Pt net counter electrode. All experiments were performed at 25 ° C. Potentials in experiments involving a reference electrode are quoted against the Hg / HgO standard.

The efficiency of the mesoporous nickel deposition process was quantified by anodic stripping voltammetry. This includes scanning the potential of the mesoporous nickel working electrode from −0.45 V to 0.9 V against a saturated calomel reference electrode (SCE) in 0.2 M HCl solution at ¹ mVs ⁻¹ . It is. The counter electrode was a Pt net. The charge associated with the anodic nickel elution peak and a comparison of this charge with the deposition charge gave a deposition efficiency of 34%.

  Cyclic voltammetry and potential step experiments were performed using a custom potentiostat and ramp generator interfaced with a National Instruments data acquisition card and LabVIEW software.

To compare the electrochemical properties of mesoporous Ni and mesoporous Pd, the cyclic voltammograms of both of these electrodes in 6M KOH were overlaid in FIG. The anodic peak of Ni at 0.38 V versus Hg / HgO indicates the oxidation of Ni (OH) ₂ to NiOOH by reaction (1), followed by reduction back to Ni (OH) ₂ . Represented by the cathode peak starting at 0.4V. The latter peak represents the proton storage capacity of the electrode, ie the reversible capacity of the electrode for proton storage. In FIG. 2, this is 295 mCcm ⁻² .

The electrochemistry of H ₁ Pd in 6M KOH is more diverse in anodic current due to oxide formation at positive potential and subsequent stripping of this oxide at the cathode peak of -0.25V. is there. Adsorption of hydrogen adatoms onto the Pd surface due to the formation of surface palladium hydride is indicated by a small cathode peak near -0.75V, which is subsequently added to the hydrogen generation current at potentials below -1V. Larger amounts of hydrogen are absorbed into the Pd lattice as indicated by the large current. In the positive potential reversal, hydrogen begins to desorb from Pd, as represented by the large anode peak that begins at -0.8V and peaks at -0.36V. Based on a voltammetric comparison of mesoporous Ni and mesoporous Pd, a charge storage device using these two electrodes can be expected to have a discharge voltage of about 1.2V. Because this is almost the start of H ⁺ desorption from Pd (−0.8 V for Hg / HgO) and intercalation of H ⁺ to NiOOH (0.4 V for Hg / HgO). This is because of the potential difference between the two. This discharge voltage is variable with the state of charge of Pd, and is −0.8 V for Hg / HgO and −0.3 V for Hg / HgO of a fully charged electrode (Pd is 20 mVs ^−1). In which hydrogen is completely released).

[(V) Supercapacitor assembly and charge / discharge characteristics test]
In order to study the performance and limitations of mesoporous nickel in a supercapacitor configuration, a negative electrode with higher capacity and power capability was required. For this purpose, the liquid crystal templated mesoporous palladium produced in the above (iii) was used. The size of the mesoporous palladium electrode was made much larger than that of the mesoporous nickel electrode, as the performance limit was due to the limitation of the nickel electrode.

Thus, a separatorless two-electrode supercapacitor was assembled using a mesoporous nickel cathode with a diameter of about 1 μm and a diameter of 200 μm with a 1 cm ² mesoporous palladium electrode separated by 1 cm in 6 M KOH solution. As prepared in (ii) above, the deposition charge in the synthesis of mesoporous nickel in this case was −1.13 mC. Taking into account the deposition efficiency of 34%, this corresponds to a mass of 0.117 μg.

FIG. 3 shows a cyclic voltammogram of a two-electrode supercapacitor that is cycled in the potential range of 0V to 1.3V. At about 1.22 V, the device is charged in response to proton removal from Ni (OH) ₂ and formation of NiOOH. As indicated by the cathode peak, a discharge occurs when protons from the Pd lattice move into the NiOOH structure to reform Ni (OH) ₂ . The discharge current in this 20 mVs ⁻¹ cycle peaks at 67 mAcm ⁻² and the total charge passing through is 257 mCcm ⁻² .

  The shape of the voltammogram of FIG. 3 is more similar to the shape of the battery than the supercapacitor. Here, as clearly shown by FIG. 4, most of the charge in the discharge passes above 1.18V.

To determine how quickly the supercapacitor is charged and discharged, the device potential was stepped from 0 V (discharged state) to 1.3 V (charged state) and the current response was measured at 25 ° C. FIG. 5 shows a single charge / discharge step sequence. During the anode spike, 800 mCcm ^-2 of charge passes. The discharge of the device is represented by a large cathode spike with a maximum amplitude of 50 Acm ⁻² when protons move into NiOOH. Here, 276 mCcm ⁻² passes through during the discharge step, of which 222 mCcm ⁻² (7 × 10 ⁻⁵ C over diameter 200 μm, or 166 mA.hg ⁻¹ ) passes in the first 50 milliseconds.

[(Vi) Supercapacitor assembly and cycle life test]
In order to test the cycle life, a supercapacitor composed of a mesoporous nickel electrode and a palladium electrode as prepared in the above (ii) and (iii) deposited on a 1 cm ² vapor-deposited gold substrate was assembled, and mesoporous The Ni electrode and the mesoporous Pd electrode were separated by a porous PTFE membrane filled with 6M KOH. The cyclability of nickel-palladium supercapacitors was investigated by cycling the device continuously at 500 mVs ⁻¹ in the potential range of 0V to 1.2V. All performance data is quoted in units related to the mass or geometric area of the nickel electrode.

As shown in FIG. 6, the shape of the voltammogram is quite different from the shape given in FIG. The peaks are fairly wide, separated by about 0.5V, compared to only 0.07V in FIG. This is due to the combination of the IR limit imposed on the cell, the introduction of a porous separator and the slow electrochemical response of Pd, and its capacity is significantly higher than the capacity of the Ni (OH) ₂ electrode of this configuration. It wasn't big. FIG. 6 compares the first 4.8 second full cycle with the 15000th cycle. A similar form of voltammogram indicates that the electrode did not degrade significantly during cycling. It is believed that the shift of the peak potential to a lower value is due to oxygen intrusion, and oxygen intrusion decreases the average hydrogen content of the palladium electrode and thus increases the negative electrode potential. The increase in charge per cycle is believed to be due to the thickening of the oxide layer during cycling.

  This result implies two things. First, mesoporous electrodes appear to be resistant to cycling decrepitation associated with other supercapacitors using insertion processes and capacity reduction in battery systems. Thus, a uniform monolithic structure such as that shown in FIG. 7 appears to withstand volume expansion and contraction strains better than a structure consisting of aggregates of sintered particles of non-uniform size distribution.

The second suggestion deals with the fact that the capacity of the mesoporous Ni electrode is not only reduced, but actually increases with cycling. By understanding that the amount of Ni (OH) _{2 in} the Ni electrode can increase over time as more Ni-based metal is oxidized under potential cycling conditions in 6M KOH, this effect is rationalized. The In effect, this increases the amount of active material in the electrode and thus increases the capacity. Several groups have already shown that by applying appropriate cycling conditions in alkaline solution, the capacity of electrodeposited Ni electrodes can be increased up to 30 times. Here, such a large increase in capacity is not expected in the configuration of the present invention, since 45% by weight of electrode material is already used during the first cycling. In any case, a large increase in capacity corresponding to complete conversion from Ni-based metal to electrically non-conductive Ni (OH) ₂ would be undesirable. This is because it can break the continuous path of Ni metal in the mesoporous electrode that provides electrical conductivity and serves as a nanoscale current collector (see FIG. 7).

[Example 10]
[Production of nanostructured nickel hydroxide / carbon supercapacitor]
[(I) Preparation of nickel substrate]
Nickel foil (10 μm thick) was obtained from Johnson Matthey and then prepared as follows to deposit mesoporous nickel.

A nickel foil electrode (4 cm ² ) was cleaned in an ultrasonic bath of isopropanol for 15 minutes prior to deposition, then rinsed with deionized water and dried under ambient conditions.

[(Ii) Electrodeposition of nickel from hexagonal liquid crystal phase]
45 wt% 0.2 M nickel acetate (II), 0.5 M sodium acetate and 0.2 M boric acid in water, and 55 wt% Brij56 (Brij is a trademark) nonionic surfactant (C ₁₆ EO _n, where n is from about 10, Aldrich available), and the mixture having a regular hexagonal topology (H _I) phase was prepared. According to the method disclosed in Chem. Mater., 2002, 14, 524-529 of Nelson et al. On a nickel foil substrate at 25 ° C. using a platinum mesh counter electrode at −0.9 V against a saturated calomel electrode. Electrodeposition was performed using a potentiostat. After deposition, the film was washed in a large amount of isopropanol for 24 hours to remove the surfactant. A mesoporous nickel film about 1 micrometer thick was obtained.

[(Iii) Production of high surface area carbon electrode]
90 wt% Norit Ultra carbon (1,200 m ² g ^-1 ), 5 wt% polytetrafluoroethylene (PTFE), 2.5 wt% acetylene black (100% compression), and 2.5 wt% A high surface area carbon electrode was made by mixing Superior graphite using a pestle and mortar. Next, the paste was manually extended into a sheet using a Durston Mini Mill rolling mill (film thickness 50 to 65 μm). A gold layer (0.5 mg cm ⁻² , about 100 nm thick) was then deposited on the carbon film to improve film conductivity. The high surface area carbon electrode had a capacity of 70-100 Fg ⁻¹ and a mass of 0.45 mg cm ⁻² .

[(Iv) Operation of Ni and carbon electrodes]
Perform cyclic voltammetry experiments using Solartron 1287 electrochemical interface and Corrware software, and perform potential step experiments using custom potentiostats and ramp generators interfaced with National Instruments data acquisition cards and LabVIEW software. went.

To compare the electrochemical properties of mesoporous Ni and high surface area carbon, cyclic voltammograms in 6M KOH for both types of electrodes are shown in FIGS. 8 and 9, respectively. At 0.46 V versus Hg / HgO, the Ni anode peak indicates oxidation of Ni (OH) ₂ to NiOOH by reaction (1), followed by the Ni peak represented by a cathode peak of 0.32 V. Reduction to (OH) ₂ occurs. The presence of Ni (OH) ₂ appears to be due to oxidation of the underlying nickel during fabrication, storage, and subsequent cycling or conditioning. The latter peak represents the proton storage capacity of the electrode, ie the reversible capacity of the electrode for proton storage. In FIG. 9, this is 0.6 V to −0.5 V for Hg / HgO and 104 mCcm ⁻² at 20 mVs ⁻¹ .

Electrochemistry of high surface area carbon electrodes in 6M KOH usually has a pure bilayer behavior and does not show any Faraday electrochemistry. The useful potential window of the carbon electrode in 6M KOH is limited only by the decomposition of the solvent, producing hydrogen at the negative limit and oxygen at the positive limit. Based on a voltammetric comparison of mesoporous Ni and high surface area carbon, it can be expected that a charge storage device using these two electrodes may have a discharge voltage of about 1.4V. This is because the onset of hydrogen generation at the carbon electrode (−1.0 V for Hg / HgO) and the intercalation of H ⁺ into NiOOH (0.4 V for Hg / HgO). This is because of the potential difference between the two.

[(V) Supercapacitor assembly and charge / discharge characteristics test]
In order to study the performance and limitations of mesoporous nickel in a supercapacitor configuration, a negative electrode with higher capacity and power capability was required. For this purpose, the high surface area carbon film prepared in (iii) above was used. The charge storage capacity of the high surface area carbon electrode was made much larger than the mesoporous nickel electrode, as the performance limit was due to the limit at the nickel electrode.

Thus, in 6M KOH solution, with two 4cm ² high surface area carbon electrodes (made in (iii) above) on each side of the nickel electrode, in each case separated by a 25 μm Celgard separator using mesoporous nickel positive electrode of about 12 [mu] m (thickness 10μm of the foil current including collector) of the double-sided 4 cm ² (active area 8 cm ²⁾ (prepared in the above (ii)), a separator (Celgard, polypropylene, 25 [mu] m, 2. A two-electrode supercapacitor with 75 mgcm ⁻² ) was assembled. The deposition charge in the synthesis of mesoporous nickel in this case produced in (ii) above was −3.9 Ccm ⁻² . This corresponds to a mass of 39.4 mg for the nickel sample containing the foil substrate, taking into account the deposition efficiency of 50%. The total mass of the two carbon electrodes was 28.5 mg, the separator was 25.8 mg, and thus the total mass of the dry capacitor was 93.7 mg.

The potential of the newly fabricated supercapacitor was cycled from 0V to 1.5V at 5 mVs ⁻¹ in a two-electrode device until the capacitor's voltammetric response was stable, at which point the charge storage capacity of the carbon and nickel electrodes was It was considered in equilibrium. There was no need to charge the positive and negative electrodes separately. FIG. 10 shows a cyclic voltammogram of a two-electrode supercapacitor that has been stabilized and then cycled in the potential range of 0V to 1.5V. At about 1.35 V, the device is charged in response to proton removal from Ni (OH) ₂ and formation of NiOOH. As indicated by the cathodic peak, discharge occurs when protons move into the NiOOH structure to reform Ni (OH) ₂ . The discharge current in this 5 mVs ⁻¹ cycle peaks at 1.3 mAcm ⁻² , and the total reduced charge passing through is 133 mCcm ⁻² .

  The shape of the voltammogram of FIG. 10 is more closely similar to the shape of the battery than the supercapacitor. Here, as clearly shown in FIG. 11, most of the charge in the discharge passes above 0.9 V for Hg / HgO.

To determine how quickly the supercapacitor is charged and discharged, the device potential was stepped from 0 V (discharged state) to 1.4 V (charged state) and the current response was measured at 25 ° C. FIG. 12 shows a single charge / discharge step sequence. During the anode spike, a charge of 105 mCcm ^-2 passes in 3 seconds. Device discharge is represented by large cathode spikes as protons migrate into the NiOOH. Here, 95 mCcm ^-2 passes during the discharge step, of which 51 mCcm ^-2 passes in the first 100 milliseconds.

[Example 11]
[Preparation of nanostructured nickel / iron supercapacitors]
[(I) Preparation of nickel substrate]
For mesoporous nickel films, nickel foil (10 μm thick, 4 cm ² ) was obtained from Johnson Matthey and then prepared as follows to deposit mesoporous nickel.

For the iron film, nickel foil (Goodflow, 10 μm, 2 cm ² ) was prepared as follows in order to deposit mesoporous iron.

  The nickel foil substrate was cleaned in an isopropanol ultrasonic bath for 15 minutes prior to deposition, then rinsed with deionized water and dried under ambient conditions.

[(Ii) Electrodeposition of nickel from hexagonal liquid crystal phase]
45 wt% 0.2 M nickel acetate (II), 0.5 M sodium acetate and 0.2 M boric acid in water, and 55 wt% Brij56 (Brij is a trademark) nonionic surfactant (C ₁₆ EO _n, n is from about 10, Aldrich available), and the mixture having a regular hexagonal topology _{(H I)} phase was prepared. According to the method disclosed in Chem. Mater., 2002, 14, 524-529 of Nelson et al. On a nickel foil substrate using a platinum net counter electrode at −0.9 V against a saturated calomel electrode at 25 ° C. Electrodeposition was performed using a potentiostat. The total deposited charge was 2.0C. After deposition, the film was washed in a large amount of isopropanol for 24 hours to remove the surfactant.

[(Iii) Electrodeposition of iron from hexagonal liquid crystal phase]
Aqueous solution and 60% by weight of Brij56 nonionic surfactant deoxygenated 40% by weight of 0.2M iron sulfate _{(II) (C 16 EO n} , where n is about 10, Aldrich) from normal the mixture having the topology of hexagonal (H _I) phase was prepared. Electrodeposition on a nickel foil substrate (area 2 cm ² ) was performed using a potentiostat at −0.9 V against a saturated calomel electrode at 25 ° C. using a platinum mesh counter electrode. After the 0.2 mAh charge passed, the film was removed from the deposition mixture under the protection of the cathode by attaching the film to a zinc foil just before the film was insulated from the deposition potential. The film was washed with a zinc foil in a large amount of deoxygenated acetone for 1 hour to remove the surfactant.

[(Iv) Iron electrode test]
After washing, the iron electrode was immersed in 6M KOH water to remove zinc. The open circuit potential was measured and found to be 1.1 V relative to the charged nanostructured NiOOH electrode. Cyclic voltammetry experiments were performed using the Solartron 1287 electrochemical interface and Corrware software.

Cyclic voltammograms of iron electrodes in 6M KOH were performed at 20 mVs- ¹ . The result is shown in FIG. This shows an anode peak of -1.0 V and a cathode peak of -1.1 V with respect to Hg / HgO. The total charge passing through the anode peak from -1.0 V to -0.3 V was 17 mC. The cathodic charge passing between -0.3V and the disturbance of hydrogen generation at -1.15V was 25 mC, as shown in FIG.

[(V) Supercapacitor assembly and charge / discharge characteristics test]
The iron and nickel electrodes produced as described above were immersed in a 6M KOH solution. The open circuit potential was measured and found to be 1.1V. The two electrodes and the solution thus constituted our capacitor for cycling tests.

The potential of the newly fabricated capacitor was cycled from 0V to 1.4V at 5 mVs- ¹ . FIG. 15 shows a cyclic voltammogram of a two-electrode supercapacitor. The discharge plotted as a negative current shows a wide peak with a peak current of 0.15 mA around 1.1V. The total charge stored was found to be 12 mC by integration of the voltammogram of FIG.

FIG. 4 represents a schematic diagram showing proton flow in the charge and discharge to and from the Pd lattice and from the Pd lattice to the NiOOH cathode proton sink. In KOH in 20MVs ^-1 of 6M, _H I Pd disk cyclic voltammetry with a diameter 1 mm - shows a comparison of the, 200 [mu] m of _H I Ni disk cyclic voltammetry (----) (). FIG. 4 shows the charge / discharge behavior of a supercapacitor based on a 200 μm H ₁ Ni disk by cyclic voltammetry at 20 mVs ⁻¹ separated by 1 cm in 6 M KOH. FIG. 4 shows the charge flow from the device versus the potential during the 20 mVs ⁻¹ discharge shown in FIG. Consisting of 6M of 1 cm ² in KOH _H I Pd 200μm in _H I Ni disc with electrodes, showing the potential step charging / discharging of the _H I Ni _{/ H} I Pd supercapacitor 6M in KOH. In 500MVs ^-1, incorporating a porous PTFE separator _{^{1cm 2 H I Ni / 1cm 2}} H I Pd super first full cycle of the capacitor (-) and (thin line), 15,000 th cycle (-) (thick line) Comparison with is shown. Shows pores surrounded by oxide active material Ni (OH) ₂ which is held in a matrix of nickel current collector, a schematic diagram of the H _I electrode structure showing active material further accounts for 45% of the bulk area of the electrode To express. FIG. 3 shows a cyclic voltammogram of the nanostructured nickel / nickel hydroxide electrode produced in Example 10. FIG. FIG. 6 shows a cyclic voltammogram of the high surface area carbon electrode produced in Example 10. FIG. 10 shows a cyclic voltammogram of a nickel-carbon supercapacitor produced in Example 10. FIG. FIG. 11 shows the potential-charge relationship of the cyclic voltammogram of the nickel-carbon supercapacitor of FIG. FIG. 11 shows the potential steps of the nickel-carbon supercapacitor (8 cm ² , 93.7 mg) of FIG. 10 pulsed from 0 V to 1.4 V in 6 M KOH at 25 ° C. FIG. Cyclic voltammograms of liquid crystal templated iron electrodes from -0.3 V to -1.2 V versus Hg / HgO in 6 M KOH at 20 mVs ⁻¹ and 25 ° C. as prepared in Example 11. Show. The potential-charge relationship of the cyclic voltammogram shown in FIG. 13 is shown. Figure 5 shows a cyclic voltammogram of mesoporous nickel versus liquid crystal templated iron in a 0V to 1.4V two-electrode device in 6M KOH at 5mVs ^-1 and 25 ° C as made in Example 11. The potential-charge relationship of the cyclic voltammogram shown in FIG. 15 is shown.

Claims (12)

A portable electronic device comprising an electrochemical cell having a positive electrode, a negative electrode and an electrolyte,
The active material of the positive electrode has a periodic arrangement of substantially uniform pores having a cross section of 10 ⁻⁸ to 10 ⁻⁹ m, and platinum, nickel, nickel hydroxide (Ni (OH) ₂ ) or consists mesoporous material formed of a material selected from nickel oxyhydroxide (NiOOH), the active material of the negative electrode, palladium, portable, characterized in that it consists of mesoporous material selected from iron or carbon Electronic devices.   The portable electronic device of claim 1, wherein the mesoporous material has a pore diameter in the range of 1 to 10 nm. The portable electronic device according to claim 1, wherein the mesoporous material has a pore number density of 4 × 10 ^{11 to} 3 × 10 ¹³ pores / cm ² .   The portable electronic device according to any one of claims 1 to 3, wherein at least 85% of the pores of the mesoporous material have a pore diameter within 30% of the average pore diameter.   The portable electronic device according to any one of claims 1 to 4, wherein the mesoporous material has a hexagonal arrangement of pores that are continuous through the thickness of the electrode.   The portable electronic device according to claim 5, wherein the hexagonal arrangement of the pores has a pore periodicity in the range of 5 to 9 nm. The negative electrode active material is, in any one of claims 1 to 6 comprising a mesoporous material having a periodic array of 10 ^-8 to 10 ^-9 substantially pores of uniform size of the cross section of the m The portable electronic device as described.   The portable electronic device according to any one of claims 1 to 7, wherein the mesoporous material is a film having a thickness in the range of 0.5 to 5 micrometers.   The portable electronic device according to any one of claims 1 to 8, wherein the mesoporous material of the negative electrode is selected from carbon and palladium. The positive electrode mesoporous material includes nickel and nickel hydroxide (Ni (OH) ₂ ) or nickel oxyhydroxide (NiOOH), and the nickel hydroxide or the nickel oxyhydroxide is a surface layer on the nickel. The portable electronic device according to any one of claims 1 to 9, wherein the mesoporous material of the negative electrode is selected from carbon or palladium. The positive electrode mesoporous material includes nickel and nickel hydroxide (Ni (OH) ₂ ) or nickel oxyhydroxide (NiOOH), and the nickel hydroxide or the nickel oxyhydroxide is a surface layer on the nickel. The portable electronic device according to claim 1, wherein the mesoporous material of the negative electrode includes nanoparticulate carbon.   The portable electronic device according to claim 1, wherein the cell is configured to function as a battery, a supercapacitor, or a combined battery / supercapacitor.

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