JP2012188728A - Composite hydrogen-storage alloy and nickel-metal hydride storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite hydrogen storage alloy having high discharging capacity and highly efficient discharging performance, and a nickel-metal hydride storage battery using the alloy.SOLUTION: The composite hydrogen storage alloy contains a hydrogen storage alloy having an I-phase and a hydrogen storage alloy having an ABtype crystal phase.

Description

  The present invention relates to a composite hydrogen storage alloy having a high discharge capacity and a high rate discharge performance, and a nickel metal hydride storage battery using the same.

  The hydrogen storage alloy is a material that can be stored safely and easily and is expected as a clean energy source, and has attracted attention as a new energy storage and conversion material.

Conventionally, as hydrogen storage alloys, those containing crystal phases such as AB ₅ type having a CaCu ₅ type structure, AB type having a CsCI type structure, AB ₂ type having a cubic C15 structure and a hexagonal C14 structure are included. Its electrochemical properties have been extensively investigated.

  On the other hand, an alloy having a 5-fold symmetry axis and a regular icosahedron structure and made of a transition metal such as Ti, Zr, and Ni is known to have an Icosahedral type quasicrystalline phase (I phase), and its high Hydrogen storage capacity has attracted attention (Non-Patent Document 1).

  The response fields of such hydrogen storage alloys include hydrogen storage / transport, heat storage / transport, thermal-mechanical energy conversion, hydrogen separation / purification, hydrogen isotope separation, nickel-metal hydride storage batteries, catalysts in synthetic chemistry However, nickel-metal hydride storage batteries using a hydrogen storage alloy as a negative electrode active material are in increasing demand because they have advantages such as small size, light weight and high output.

As a negative electrode active material of a nickel metal hydride storage battery, an AB ₅ type alloy containing rare earth elements and Ni as main constituent elements has been used in the past. However, the discharge capacity of the AB ₅ type alloy currently used is already LaNi ₅ . The capacity has reached about 85% of the theoretical capacity, and no further increase in capacity can be expected.

Appl.Phys.Lett.69 (1996) 2998-3000

  In view of the above, the present invention is intended to provide a composite hydrogen storage alloy having a high discharge capacity and a high rate discharge performance, and a nickel metal hydride storage battery using the same.

The present inventors have conducted extensive studies results, the hydrogen storage alloy having a superior phase I having a hydrogen storage capacity, by composite alloying a mixture of hydrogen-absorbing alloy of AB ₃ type crystal phase, hydrogen It has been found that the release ability can be improved, and the present invention has been completed.

That is, the composite hydrogen storage alloy according to the present invention includes a hydrogen storage alloy having an I phase and a hydrogen storage alloy having an AB ₃ type crystal phase.

In the composite hydrogen storage alloy according to the present invention, the content of the hydrogen storage alloy having the AB ₃ type crystal phase is preferably 10 to 30% by weight in the composite hydrogen storage alloy.

  The hydrogen storage alloy having the I phase preferably includes at least Ti as a constituent element, and more preferably includes at least Ti, V, and Ni as constituent elements.

  Although it does not specifically limit as a use of the composite hydrogen storage alloy which concerns on this invention, It can use suitably as a negative electrode active material of a nickel hydride storage battery. Thus, the nickel hydride storage battery provided with the negative electrode containing the composite hydrogen storage alloy which concerns on this invention is also one of this invention.

According to the present invention, a hydrogen storage alloy having an I phase having an excellent hydrogen storage ability is mixed with a hydrogen storage alloy having an AB ₃ type crystal phase to form a composite alloy, thereby improving the hydrogen release ability. Can be achieved. And, by using such a composite hydrogen storage alloy having both excellent hydrogen storage capacity and hydrogen release capacity as a negative electrode active material for a nickel metal hydride storage battery, the battery has a high discharge capacity and excellent high rate discharge performance. Can be obtained.

AB ₃ type alloys _{(a), Ti 1.4 V 0.6} Ni alloy (b), and is a view showing an XRD pattern of their complex alloy (c). Bright field image (a), 5 times electron diffraction pattern (b), and normal electron diffraction pattern (c) of Ti _1.4 V _0.6 Ni alloy observed with a transmission electron microscope (TEM) FIG. Shows a negative electrode consisting of Ti _1.4 V _0.6 Ni _alloy, the negative electrode comprising a composite alloy of Ti _{1.4 V 0.6} Ni alloy and AB ₃ type alloys, the correlation between the discharge capacity and cycle times It is a graph. A negative electrode consisting of Ti _1.4 V _0.6 Ni _alloy, the negative electrode comprising a composite alloy of Ti _{1.4 V 0.6} Ni alloy and AB ₃ type alloys, the spectrum of the electrochemical impedance at 50% DOD It is a graph which shows. It is a figure which shows the equivalent circuit corresponding to the spectrum of the electrochemical impedance shown in FIG. A semi-logarithmic plot of anode current versus current time response for a negative electrode made of Ti _1.4 V _0.6 Ni alloy and a negative electrode made of a composite alloy of Ti _1.4 V _0.6 Ni alloy and AB ₃ type alloy It is a graph which shows.

  The present invention is described in detail below.

The composite hydrogen storage alloy according to the present invention contains a hydrogen storage alloy having an I phase and a hydrogen storage alloy having an AB ₃ type crystal phase. Here, the I phase means an Icosahedral type quasicrystalline phase, and the AB ₃ type crystalline phase means a crystalline phase having a composition represented by AB ₃ . A represents at least one element (hydrogen storage metal) selected from the group consisting of rare earth elements and Mg, and B represents at least one element selected from the group consisting of transition elements other than rare earth elements and Al. (Hydrogen releasing metal).

Examples of the hydrogen storage alloy having the I phase include Ti _1.4 V _0.6 Ni, Ti _1.6 V _0.4 Ni, Ti _1.7 V _0.3 Ni, Ti _1.8 V _{0. 2} Ni, Ti _1.9 V _0.1 Ni, Ti ₄₅ Zr ₃₀ Ni ₁₃ Pd ₇ , Ti ₄₅ Zr ₃₀ Ni ₂₅ Y, Ti ₄₅ Zr ₃₅ Ni ₁₇ Cu ₃ , Ti ₄₅ Zr ₃₈ Ni ₁₇ , Ti ₅₉ Ni ₃₄ titanium-based alloys such as V _7; Mg ₂₅ Y 11 magnesium-based alloys such as _{Zn 64; Al 63 Cu 25 Fe} 12, Al 70 Cu 20 Fe 10, Al 86 Mn 14, Al 56.1 Cu 10.2 Li 33. ₇ , Al _85.7 V _14.3 , Al _78.4 Mn _10.6 Ru ₄ , Al _80.4 Mn _19.6 , Al ₇₈ Re ₂₂ , Al ₆ Mn, etc. Sc-based alloys such as Sc _16.2 Cu _12.3 Zn _71.5 ; zinc-based alloys such as Zn ₅₉ Mg ₃₁ Ho _{10 and the} like. These are all alloys having an Icosahedral type quasicrystalline phase, and may be used alone or in combination of two or more. Among these alloys, a titanium-based alloy containing Ti as a main constituent element is preferably used because of its excellent hydrogen storage capacity, and a Ti content of 45 at% or more is more preferable.

As the titanium-based alloy, TiZrNi-based alloys having Ti, Zr and Ni as constituent elements are widely used because of their excellent stability, but at least a part of Zr in the TiZrNi-based alloy is replaced with V. The TiVNi-based alloy thus produced has a higher dynamic effect (activity) than the TiZrNi-based alloy and is excellent in hydrogen releasing ability. Further, since V is less expensive than Zr, TiVNi-based alloys are more advantageous in terms of cost than TiZrNi-based alloys. Among such titanium-based alloys containing at least Ti, V and Ni as constituent elements, for example, the general formula Ti _x V _y Ni (1.4 ≦ x ≦ 1.9, 0.1 ≦ y ≦ 0.6) , X + y = 2) is preferably used.

  The content of the I phase in the hydrogen storage alloy having the I phase is preferably 30 to 70% by volume in the hydrogen storage alloy. When the content of the I phase is less than 30% by volume, the hydrogen storage amount may be sufficient. On the other hand, when the content of the I phase exceeds 70% by volume, the hydrogen releasing ability may be lowered.

  The method for producing the hydrogen storage alloy having the I phase is not particularly limited. For example, melting such as a single roll melt spinning method, a twin roll melt spinning method, a centrifugal spray method, a REP method, a spinning in a rotating liquid, and a gas atomizing method. A method of rapidly cooling an alloy in a state; a solid phase reaction method such as a mechanical alloying method; a method of forming from a gas phase such as a sputtering method, and the like. A hydrogen storage alloy having a phase can be produced.

The hydrogen storage alloy having the AB ₃ type crystal phase is not particularly limited, and examples thereof include those represented by the composition of AB _{3.0 to} AB _3.8 . General formula La _a Mg _b M _1-ab Ni _c M2 _d (where 0.3 ≦ a ≦ 0.65, 0.15 ≦ b ≦ 0.3, 2.5 ≦ c ≦ 3.8, 3 ≦ c + d ≦ 3.8, M1 represents at least one element selected from the group consisting of rare earth elements other than La, and M2 represents a transition element excluding rare earth elements and Ni and a group consisting of Al And an alloy having a composition represented by at least one selected element).

As an alloy having such a composition represented by the general formula, for example, La _a Nd _b Mg _1-a-b Ni _c Al _3-c (0.60 ≦ a ≦ 0.65, 0.10 ≦ b _{≦ 0.12,2.5 ≦ c <3),} La a Nd b Mg 1-a-b Ni 2.85 Co c Si d Al 1-c-d (0.50 ≦ a ≦ 0.52,0 .25 ≦ b ≦ 0.30, 0.60 ≦ c ≦ 0.70, 0 ≦ d ≦ 0.10), La _a Nd _b Y _c Mg _1- abc _c Ni _d Co _e Si _f Al _g (0.30 ≦ a ≦ 0.40, 0.10 ≦ b ≦ 0.20, 0.1 ≦ c ≦ 0.20, 2.5 ≦ d ≦ 2.7, 0.30 ≦ e ≦ 0.40 , 0 ≦ f ≦ 0.10,0 ≦ g ≦ 0.10) , and the like, more specifically, for _{example, La 0.65 Nd 0.12 Mg 0.23 Ni} 2.9 Al 0.1 _{La 0.52 Nd 0.30 Mg 0.18 Ni 2.85} Co 0.70 Si 0.10 Al 0.15, La 0.4 Nd 0.2 Y 0.2 Mg 0.2 Ni 2.7 Co _0.4 Si _0.1 Al _0.1 etc. are mentioned. These alloys may be used independently and 2 or more types may be used together.

The method for producing the hydrogen storage alloy having the AB ₃ type crystal phase is not particularly limited, and examples thereof include an induction floating melting method, a sintering method, a rapid solidification method, and the like. A hydrogen storage alloy having the AB ₃ type crystal phase can be manufactured.

The composite hydrogen storage alloy according to the present invention is obtained by adding a hydrogen storage alloy having an AB ₃ type crystal phase to a hydrogen storage alloy having an I phase, and converting them into a composite alloy. _The type ₃ crystal phase promotes the movement of atomic hydrogen, and as a result, the hydrogen releasing ability can be improved. Therefore, the composite hydrogen storage alloy according to the present invention containing the hydrogen storage alloy having the I phase and the hydrogen storage alloy having the AB ₃ type crystal phase has a discharge capacity higher than that of the hydrogen storage alloy having the I phase alone. Large and excellent in high rate discharge performance.

In the present invention, the mixing ratio of the hydrogen storage alloy having a hydrogen storage alloy and AB ₃ type crystal phase having a phase I, the hydrogen storage alloy having the obtained composite hydrogen storage alloy AB ₃ type crystal phase It is preferable to add a hydrogen storage alloy having an AB ₃ type crystal phase to a hydrogen storage alloy having an I phase so that the content is 10 to 30% by weight and to mix them. If the content of the hydrogen storage alloy having the AB ₃ type crystal phase is less than 10% by weight, the hydrogen releasing ability may be insufficient, while the hydrogen storage alloy having the AB ₃ type crystal phase may be insufficient. Even if the content exceeds 30% by weight, no further improvement effect on the discharge capacity can be expected, and the content of the hydrogen storage alloy having the I phase is reduced accordingly, so that the hydrogen storage capacity is insufficient. It may become.

The method for producing a composite hydrogen storage alloy according to the present invention is not particularly limited. For example, a hydrogen storage alloy having an I phase manufactured by using a single roll melt spinning method or the like so as to have a predetermined composition. The hydrogen storage alloy having the AB ₃ type crystal phase produced by using the induction suspension method or the like was mechanically pulverized and pulverized, and then mixed at a predetermined mixing ratio. The composite hydrogen storage alloy according to the present invention can be manufactured by subjecting the mixture to mechanical alloying treatment.

The presence of the quasicrystalline phase or the crystalline phase in the composite hydrogen storage alloy according to the present invention, and the hydrogen storage alloy having the I phase as the raw material and the hydrogen storage alloy having the AB ₃ type crystal phase is, for example, This can be confirmed using an X-ray diffraction method (XRD) or a transmission electron microscope (TEM).

  The use of the composite hydrogen storage alloy according to the present invention is not particularly limited and can be applied to various uses including nickel-metal hydride storage batteries, fuel cells, fuel tanks for hydrogen automobiles, etc. It is suitably used as a negative electrode active material for nickel-metal hydride storage batteries. Thus, the nickel metal hydride storage battery provided with the negative electrode containing the composite hydrogen storage alloy according to the present invention is also one aspect of the present invention.

  The nickel metal hydride storage battery according to the present invention includes, for example, a positive electrode (nickel) containing a positive electrode active material mainly composed of nickel hydroxide in addition to a negative electrode containing the composite hydrogen storage alloy according to the present invention as a negative electrode active material. Electrode), a separator, an alkaline electrolyte, and the like.

  The negative electrode is one in which the composite hydrogen storage alloy according to the present invention is blended as a negative electrode active material. The composite hydrogen storage alloy which concerns on this invention is mix | blended in a negative electrode as powdered composite hydrogen storage alloy powder, for example.

  The composite hydrogen storage alloy powder preferably has an average particle size of 20 to 100 μm, more preferably 40 to 70 μm. When the average particle size is less than 20 μm, the activation of the alloy becomes insufficient, while when the average particle size exceeds 100 μm, the productivity may be lowered. The composite hydrogen storage alloy powder is obtained, for example, by pulverizing the composite hydrogen storage alloy according to the present invention with a machine in the presence of an inert gas.

  The negative electrode may contain a conductive agent, a binder (thickening agent) and the like in addition to the composite hydrogen storage alloy powder.

  Examples of the conductive agent include natural graphite (scale-like graphite, scale-like graphite, earth-like graphite, etc.), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker, carbon fiber, vapor-grown carbon, etc. Examples thereof include metal-based conductive agents; metal-based conductive agents composed of powders or fibers of metals such as nickel, cobalt, and copper; yttrium oxide. These electrically conductive agents may be used independently and 2 or more types may be used together.

  The blending amount of the conductive agent is preferably 0.1 to 10 parts by mass, more preferably 0.2 to 5 parts by mass with respect to 100 parts by mass of the composite hydrogen storage alloy powder. If the blending amount of the conductive agent is less than 0.1 parts by mass, it is difficult to obtain sufficient conductivity. May be sufficient.

  Examples of the binder include polytetrafluoroethylene (PTFE), polyolefin resins such as polyethylene and polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene butadiene rubber (SBR), and fluorine rubber. , Polyvinyl alcohol, methyl cellulose, carboxymethyl cellulose, xanthan gum and the like. These binders may be used independently and 2 or more types may be used together.

  The amount of the binder is preferably 0.1 to 0.5 parts by mass, more preferably 0.1 to 0.3 parts by mass with respect to 100 parts by mass of the composite hydrogen storage alloy powder. is there. When the blending amount of the binder is less than 0.1 parts by mass, sufficient thickening is difficult to be obtained. On the other hand, when the blending amount of the binder exceeds 0.5 parts by mass, the performance of the electrode is improved. May fall.

  Examples of the positive electrode include an electrode in which a nickel hydroxide composite oxide obtained by mixing zinc hydroxide or cobalt hydroxide with nickel hydroxide as a main component is blended as a positive electrode active material. As the nickel hydroxide composite oxide, those uniformly dispersed by a coprecipitation method are preferably used.

The positive electrode preferably contains an additive for improving electrode performance in addition to the nickel hydroxide composite oxide. Examples of the additive include conductive modifiers such as cobalt hydroxide and cobalt oxide, and the nickel hydroxide composite oxide coated with cobalt hydroxide, and the nickel hydroxide composite oxide. Part of the product may be oxidized with oxygen or oxygen-containing gas, K ₂ S ₂ O ₈ , hypochlorous acid, or the like.

  As the additive, a compound containing a rare earth element such as Y or Yb, or a substance that improves oxygen overvoltage such as a Ca compound can also be used. Since some of rare earth elements such as Y and Yb are dissolved and disposed on the negative electrode surface, an effect of suppressing corrosion of the negative electrode active material can be expected.

  The positive electrode may further contain the above-described conductive agent, binder and the like, similarly to the negative electrode.

  Such a positive electrode and a negative electrode were obtained by kneading these with water or an organic solvent such as alcohol or toluene after adding the above-mentioned conductive agent, binder, or the like to each active material as necessary. The paste can be produced by applying it to a conductive support and drying it, followed by rolling.

  Examples of the conductive support include a steel plate and a plated steel plate obtained by plating a steel plate with a metal material such as nickel. Examples of the shape of the conductive support include a foam, a molded product of a fiber group, a three-dimensional base material subjected to unevenness processing, and a two-dimensional base material such as a punching plate. Of these conductive supports, for the positive electrode, a foam made of nickel having excellent corrosion resistance and oxidation resistance with respect to alkali and having a porous structure having a current collecting property is preferable. On the other hand, for a negative electrode, a punching plate obtained by applying nickel plating to an iron foil that is inexpensive and excellent in conductivity is preferable.

  The thickness of the conductive support is preferably 30 to 100 μm, more preferably 40 to 70 μm. When the thickness of the conductive support is less than 30 μm, the productivity may be reduced. On the other hand, when the thickness of the conductive support exceeds 100 μm, the discharge capacity may be insufficient. .

  When the conductive support is porous, the inner diameter is preferably 0.8 to 2 μm, more preferably 1 to 1.5 μm. If the inner diameter is less than 0.8 μm, the productivity may be lowered. On the other hand, if the inner diameter exceeds 2 μm, the holding performance of the hydrogen storage alloy may be insufficient.

  Examples of a method for applying each electrode paste to the conductive support include roller coating using an applicator roll and the like, screen coating, blade coating, spin coating, and per coating.

  Examples of the separator include a porous film and a nonwoven fabric made of a polyolefin resin such as polyethylene or polypropylene, acrylic, polyamide, or the like.

The basis weight of the separator is preferably 40 to 100 g / m ² . If the basis weight is less than 40 g / m ² , a short circuit or a decrease in self-discharge performance may occur. On the other hand, if the basis weight exceeds 100 g / m ² , the proportion of the separator per unit volume increases. Tend to go down. The separator preferably has an air permeability of 1 to 50 cm / sec. If the air permeability is less than 1 cm / sec, the internal pressure of the battery may be too high. On the other hand, if the air permeability exceeds 50 cm / sec, a short circuit or a decrease in self-discharge performance may occur. Furthermore, the average fiber diameter of the separator is preferably 1 to 20 μm. If the average fiber diameter is less than 1 μm, the strength of the separator may decrease, and the defect rate in the battery assembly process may increase. On the other hand, if the average fiber diameter exceeds 20 μm, the average fiber diameter may cause a short circuit or a decrease in self-discharge performance. Sometimes.

The separator is preferably subjected to a hydrophilic treatment on the fiber surface. Examples of the hydrophilization treatment include sulfonation treatment, corona treatment, fluorine gas treatment, and plasma treatment. Among them, the separator whose fiber surface has been sulfonated has a high ability to adsorb impurities such as NO ₃ ⁻ , NO ₂ ⁻ , NH ₃ ^{− and the} like, which cause a shuttle phenomenon, and an elution element from the negative electrode. The suppression effect is high and preferable.

  Examples of the alkaline electrolyte include alkaline aqueous solutions containing potassium hydroxide, sodium hydroxide, lithium hydroxide and the like. The said alkaline electrolyte may be used independently and 2 or more types may be used together.

  The concentration of the alkaline electrolyte is preferably a total ion concentration of 9.0 mol / L or less, more preferably 5.0 to 8.0 mol / L.

  Various additives may be added to the alkaline electrolyte in order to improve oxygen overvoltage at the positive electrode, improve corrosion resistance of the negative electrode, and improve self-discharge. Examples of such additives include oxides and hydroxides such as yttrium, ytterbium, erbium, calcium, and zinc. These additives may be used independently and 2 or more types may be used together.

  When the nickel-metal hydride storage battery according to the present invention is an open-type nickel-metal hydride storage battery, for example, the battery is sandwiched between a negative electrode and a positive electrode via a separator, and the electrodes are fixed so that a predetermined pressure is applied to these electrodes. It can be produced by injecting an alkaline electrolyte and assembling an open cell.

  On the other hand, when the nickel-metal hydride storage battery according to the present invention is a sealed nickel-metal hydride storage battery, the battery is injected with an alkaline electrolyte before or after the positive electrode, the separator, and the negative electrode are stacked, and sealed with an exterior material. Can be manufactured. Further, in a sealed nickel-metal hydride storage battery in which a power generation element in which a positive electrode and a negative electrode are stacked via a separator is wound, an alkaline electrolyte is injected into the power generation element before or after the power generation element is wound. Is preferred. The method of injecting the alkaline electrolyte is not particularly limited, and may be injected at normal pressure. For example, a vacuum impregnation method, a pressure impregnation method, a centrifugal impregnation method, or the like may be used. Moreover, as an exterior material of a sealed nickel-metal hydride storage battery, for example, a material made of iron, stainless steel, polyolefin resin, or the like plated with a metal material such as iron or nickel can be cited.

  The embodiment of the sealed nickel-metal hydride storage battery is not particularly limited. For example, a battery including a positive electrode such as a coin battery, a button battery, a square battery, and a flat battery, a negative electrode, and a single-layer or multi-layer separator, a roll And a cylindrical battery including a positive electrode, a negative electrode and a separator.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

<Test method>
A strip of Ti _1.4 V _0.6 Ni alloy having a width of 2.5 mm and a thickness of 35 μm was prepared using a single roll melt spinning method in an argon atmosphere. The peripheral speed of the copper wheel at this time was 34 m / s. An AB ₃ type alloy having a composition of La _0.65 Nd _0.12 Mg _0.23 Ni _2.9 Al _0.1 was prepared using an induction floating dissolution method in an argon atmosphere. Samples of Ti _1.4 V _0.6 Ni alloy and AB type ₃ alloy are mechanically pulverized and ground to 200-400 mesh powder, 80 wt% Ti _1.4 V _0.6 Ni alloy And a 20% by weight AB ₃ type alloy powder mixture were subjected to a mechanical alloying treatment for 30 minutes with a high energy ball mill. The phase of the band of the prepared composite alloy was examined by X-ray diffraction (XRD), and the microstructure was examined by transmission electron microscope (TEM).

The prepared composite alloy powder was mixed with carbonyl nickel powder at a weight ratio of 1: 5 to prepare a negative electrode. A pressure of 15 MPa was applied to the obtained powder mixture to compress it into small pellets having a diameter of 10 mm and a thickness of 1.5 mm. For electrochemical measurement, a half-cell was fabricated using a Ni (OH) ₂ / NiOOH electrode as a counter electrode, a Hg / HgO electrode as a reference electrode, and a working electrode in an electrolyte solution of 6 M KOH. did. The electrochemical test was conducted at 303K using an automatic constant current charging / discharging device (DC-5). The negative electrode was charged at 60 mA / g for 6 hours and discharged at 30 mA / g to a final voltage of −0.6 V (vs. Hg / HgO). 50% depth discharge (DOD) using a Solarton 1287 Potentiostat / Galvanostat paused for 5 minutes per charge / discharge and a Solarton 1255B frequency response analyzer with Z-PLOT software for Windows Then, electrochemical impedance spectroscopy (EIS) analysis was performed. In this test, the constant voltage discharge method was selected to evaluate the effect of hydrogen diffusion at a given electrode. After a full charge following an open circuit 30 minutes, the test electrodes were discharged with a potential step of +500 mV for 3600 seconds with an EG & G PARC model 273 potentiostat / galvanostat using M352 corrosion software.

<Result>
(1) Phase structure FIG. 1 shows XRD patterns of AB type ₃ alloy, Ti _1.4 V _0.6 Ni alloy, and composite alloys thereof. The AB ₃ type alloy is shown in FIG. 1 (a), and the alloy mainly includes a (La, Mg) Ni ₃ phase having a PuNi ₃ type surface body crystal structure (space group R3m) and a hexagonal CaCu ₅ system. It was observed to consist of LaNi ₅ phase with a crystal structure (space group P6 / mmm). The diffraction peaks in FIG. 1B corresponding to the Ti _1.4 V _0.6 Ni alloy are the I phase, the Ti ₂ Ni type face centered cubic lattice structure (FCC) phase, and the body centered cubic lattice structure (BCC). ) Showed a solid solution phase. After the mixture of Ti _1.4 V _0.6 Ni alloy and AB ₃ type alloy was pulverized by a ball mill (FIG. 1 (c)), the anisotropy of the crystal lattice was increased, resulting in (La, Mg) Ni. The diffraction peaks of the ₃ phase and the LaNi ₅ phase were clearly broad.

FIG. 2 (a) is a bright field image showing typical growth morphology and the presence of I-phase nodules. For the point group symmetry and crystalline BCC phase of the I phase, the expected fivefold and normal electron diffraction patterns (001) are observed, respectively, as shown in FIGS. 2 (b) and 2 (c). It was. Although electron diffraction patterns corresponding to (La, Mg) Ni ₃ phase, LaNi ₅ phase and Ti ₂ Ni type FCC phase were not observed, the XRD results (FIG. 1) clearly show their phases in the composite alloy sample. The presence of This phenomenon can occur because other crystalline phases formed from liquids under different conditions usually precipitate in different regions of the sample in this way.

(2) discharge capacity and stability Figure _3, a negative electrode consisting of Ti _{1.4 V 0.6} Ni _alloy, a negative electrode comprising a composite alloy of Ti _{1.4 V 0.6} Ni alloy and AB ₃ type alloys It is a graph which shows the correlation of the number of cycles of this, and discharge capacity. The discharge capacity was significantly improved by the addition of AB type ₃ alloy. When no AB ₃ type alloy is added, the discharge capacity reaches the highest value of 272.7 mAh / g in the second cycle, and an AB ₃ type alloy having higher hydrogen storage properties (340 mAh / g) is added. After adding 20% by weight of AB ₃ type alloy, the maximum value of 294.7 mAh / g was reached in the first cycle. This indicates that there is a synergistic effect between the AB ₃ type alloy and the Ti _1.4 V _0.6 Ni alloy in the composite hydrogen storage alloy electrode. However, even when AB ₃ type alloy was added in an amount of 30% by weight, no further improvement in the discharge capacity was observed.

(3) and the negative electrode (a) made of high-rate discharge performance and dynamic properties Ti _1.4 V _0.6 Ni alloy, and _a complex of the Ti _{1.4 V 0.6} Ni alloy and AB ₃ type alloys Table 1 shows the high rate discharge performance (HRD) with the negative electrode (b) made of

From the results shown in Table 1, an electrode (b) made of a composite of a Ti _1.4 V _0.6 Ni alloy and an AB ₃ type alloy is an electrode (a) made of a Ti _1.4 V _0.6 Ni alloy. As a result, it was found that it has excellent high rate discharge performance. It is known that the HRD of a metal hydride (MH) electrode is mainly influenced by the charge transfer reaction occurring at the electrode / electrolyte interface and the diffusion rate of hydrogen in the electrode.

In order to evaluate the electrochemical reaction rate of an electrode composed of a composite of Ti _1.4 V _0.6 Ni alloy and AB ₃ type alloy and an electrode composed of Ti _1.4 V _0.6 Ni alloy, The spectra of chemical impedance and potential step were measured. The electrochemical impedance spectrum of both electrode samples at 50% DOD is shown in FIG. Both EIS curves were found to consist of two arcs following a straight line.

According to the analytical model proposed by Kuriyama et al. (See J. Alloys. Compd. 202 (1993) 183-197), a relatively large arc in the medium frequency region represents the charge transfer resistance to the electrochemical reaction at the surface, Here, R ₁ is an electrolyte resistance, and R ₂ and C ₁ are a contact resistance and a contact capacitance between the current collector and the alloy pellet, respectively. Contact resistance and contact capacitance between the alloy powders in the alloy pellet are represented by R ₃ and C ₂ , respectively. Each Rct and a C _3, showing the charge transfer resistance and the double layer capacitance. Wo is the Warburg resistance. Based on the equivalent circuit shown in FIG. 5, the charge transfer resistance Rct was obtained by the fitting program Z-VIEW.

According to the calculation result, the Rct of the alloy electrode increased from 0.148Ω (b) to 0.218Ω (a). It is well known that charge transfer resistance and exchange current density are determined by electrocatalytic activity. The Ti _1.4 V _0.6 Ni alloy electrode after the addition of AB ₃ type alloy had a reduced Rct. However, the result of electrochemical impedance measurement is different from the result of HRD, suggesting that surface charge transfer is not the rate-determining step.

  The hydrogen diffusion coefficient of the bulk electrode was determined by the potential step method. FIG. 6 shows that the semi-log plot of anode current versus current time response can clearly be divided into three time domains after applying an overvoltage, from the spectrum. According to the model of Zheng et al. (See J. Electrochem. Soc. 142 (1995) 2695-2699), the hydrogen diffusion coefficient at the bulk electrode used to determine the hydrogen diffusion rate is shown in the plot corresponding to Calculated from the slope of the linear region.

Where D is the hydrogen diffusion coefficient (cm ² / s), a is the radius (cm) of the spherical particles, i is the diffusion current density (A / g), and C ₀ is the initial hydrogen of the bulk electrode. The concentration (mol / cm ³ ), Cs is the hydrogen concentration (mol / cm ³ ) on the surface of the alloy particles, d is the density (g / cm ³ ) of the hydrogen storage material, and t is the discharge time. . The hydrogen diffusion coefficient D in the bulk electrode when the average particle diameter is assumed to be 15 μm was calculated by the formula (1) and shown in Table 2.

From the results shown in Table 2, the D value is in the order of Ti _1.4 V _0.6 Ni + AB ₃ (b)> Ti _1.4 V _0.6 Ni (a), which is consistent with the order of high discharge capacity. . This suggests that the diffusion process is dominant in controlling the electrochemical reaction. As described above, it is considered that the AB type ₃ alloy promotes the movement of atomic hydrogen and is effective in improving the electrochemical reaction rate.

Claims (5)

A composite hydrogen storage alloy comprising a hydrogen storage alloy having an I phase and a hydrogen storage alloy having an AB ₃ type crystal phase. 2. The composite hydrogen storage alloy according to claim 1, comprising 10 to 30% by weight of the hydrogen storage alloy having the AB ₃ type crystal phase.   The composite hydrogen storage alloy according to claim 1 or 2, wherein the hydrogen storage alloy having the I phase contains at least Ti as a constituent element.   The composite hydrogen storage alloy according to claim 1, 2 or 3, wherein the hydrogen storage alloy having the I phase contains at least Ti, V and Ni as constituent elements.   A nickel-metal hydride storage battery comprising a negative electrode containing the composite hydrogen storage alloy according to claim 1, 2, 3 or 4.