JP2019040801A - Hydrogen storage alloy electrode - Google Patents

Abstract

To provide a hydrogen storage alloy electrode with improved cycle characteristics.SOLUTION: The hydrogen storage alloy electrode has a body-centered cubic structure and includes a composite alloy having hydrogen storage alloy particles containing a TiCrV alloy and a Cr coating layer mainly composed of single Cr formed on surfaces of the hydrogen storage alloy particles.SELECTED DRAWING: Figure 1

Description

  The present application discloses a hydrogen storage alloy electrode.

  Hydrogen storage alloys are used for electrodes of alkaline batteries. As a technique related to such a hydrogen storage alloy, for example, Patent Document 1 discloses a hydrogen storage alloy electrode made of hydrogen storage alloy particles made of V, Ti, Cr, etc. and having a crystal structure of a body-centered cubic structure. .

  Patent Document 2 discloses that Ni is deposited on the surface of a hydrogen storage alloy containing Ti and having a body-centered cubic structure. Patent Document 3 discloses a Ti—Cr—V hydrogen storage alloy that is manufactured by a rapid solidification method, has a small crystal grain size, and has a Ni addition layer mainly composed of a Ti—Ni compound on the surface.

JP 11-144728 A JP 2002-141061 A Japanese Patent Laid-Open No. 11-80865

  The hydrogen storage alloy electrode disclosed in Patent Document 1 has room for improvement in cycle characteristics.

  Therefore, an object of the present disclosure is to provide a hydrogen storage alloy electrode with improved cycle characteristics.

In order to solve the above problems, the present disclosure takes the following means. That is,
The present disclosure relates to a composite alloy having a body-centered cubic structure and comprising a hydrogen storage alloy particle containing a TiCrV alloy and a Cr coat layer mainly composed of a single Cr formed on the surface of the hydrogen storage alloy particle. A hydrogen storage alloy electrode.

  In the present disclosure, “mainly composed of Cr” means that the ratio (mol%) of Cr among the components contained in the Cr coat layer is the highest.

  According to the present disclosure, it is possible to provide a hydrogen storage alloy electrode with improved cycle characteristics.

It is a figure which shows the relationship between the cycle number of a charging / discharging test, and a capacity | capacitance maintenance factor about the battery produced by the Example and the comparative example.

  Hereinafter, the present disclosure will be described. In addition, the form shown below is an illustration of this indication and this indication is not limited to the form shown below.

  The hydrogen storage alloy electrode of the present disclosure (hereinafter sometimes referred to as “electrode of the present disclosure”) includes a hydrogen storage alloy particle containing a TiCrV alloy having a body-centered cubic structure (BCC structure), and a hydrogen storage alloy particle. A composite alloy having a Cr coat layer mainly composed of a single Cr formed on the surface is provided.

The hydrogen storage alloy particles contain a TiCrV alloy having a BCC structure as a hydrogen storage alloy (hereinafter sometimes referred to as “MH”). The hydrogen storage alloy particles may contain other MH in addition to the TiCrV alloy having the BCC structure, but are preferably composed of only the TiCrV alloy having the BCC structure. For example, when the electrode of the present disclosure is used as a negative electrode of a Ni-MH secondary battery, by using a TiCrV alloy having a BCC structure as MH, AB ₅ series and A used in current Ni-MH secondary batteries are used. It can be provided with a capacity potential (for example, 760 mA / g) that is more than twice that of ₂ B _7- based MH.

  The particle size of the hydrogen storage alloy particles is not particularly limited, but is preferably 50 μm or less from the viewpoint of battery input / output.

  On the surface of the hydrogen storage alloy particles, a Cr coat layer mainly composed of simple Cr is formed. By forming a Cr coat layer on the surface of the hydrogen storage alloy particles, the elution of V from the surface of the TiCrV alloy, which is a cause of cycle deterioration (decrease in electrode capacity accompanying charge / discharge cycles), is suppressed, and cycle characteristics Can be improved.

  As a method for obtaining a composite alloy by forming a Cr coat layer on the surface of the hydrogen storage alloy particles, for example, a method of attaching a single Cr to the surface of the hydrogen storage alloy particles by a powder sputtering method (barrel sputtering method). Can be mentioned. The ratio of the portion covered with the Cr coating layer in the entire surface of the composite alloy is not particularly limited, and it is sufficient that at least a part of the surface of the composite alloy is covered. However, from the viewpoint of easily improving the cycle characteristics, it is preferable that the entire surface of the composite alloy is covered with a Cr coat layer.

  In the present disclosure, the thickness of the Cr coat layer is not particularly limited. The Cr coating layer only needs to cover the surface of the composite alloy, and it is considered that the cycle characteristics can be improved even when the thickness is about several nm. Similarly, it is considered that the cycle characteristics can be improved even if the thickness is large. However, if the thickness is too large, it is not preferable in terms of input / output of the battery. Therefore, the thickness of the Cr coat layer is preferably 10 μm or less.

  The electrode of the present disclosure only needs to have the above composite alloy, and may contain other substances in addition to the composite alloy. Examples of other substances that can be included in the electrode of the present disclosure include a conductive additive and a binder. As the conductive assistant, for example, metal particles such as Ni can be used. As the binder, carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), or the like can be used. As a method for producing an electrode of the present disclosure, a composite alloy, a conductive additive, and a binder are weighed so as to have a predetermined weight ratio, and then a paste-like composition produced by kneading these is used. Examples thereof include a method of applying to a porous conductive member and subsequently drying it, and then pressing it at a predetermined pressure.

  The electrode of the present disclosure also has a side surface as a negative electrode of an alkaline storage battery having a positive electrode, an electrolyte layer, and a negative electrode. That is, the electrode of the present disclosure can be suitably used as a negative electrode of an alkaline storage battery using a composite alloy as a negative electrode active material.

The alkaline storage battery may be, for example, a nickel metal hydride battery, an air battery, or another form. When the alkaline storage battery is a nickel metal hydride battery, for example, nickel hydroxide (Ni (OH) ₂ ) can be used for the positive electrode. On the other hand, when the alkaline storage battery is an air battery, an oxide having a perovskite structure such as LaNiO ₃ can be used for the positive electrode.

  The electrolyte layer is disposed between the positive electrode and the negative electrode and includes an alkaline aqueous solution. Examples of the alkaline aqueous solution include a potassium hydroxide (KOH) aqueous solution. Although the density | concentration of aqueous solution is not specifically limited, For example, it can be 6 mol / L. The electrolyte layer may be composed only of an electrolytic solution, or may be an impregnated electrolytic solution in a separator. As the separator, for example, a nonwoven fabric separator made of polyethylene / polypropylene can be used.

  When producing the alkaline storage battery, the electrode of the present disclosure used as the negative electrode can be produced, for example, by the method described above. On the other hand, for example, a positive electrode is prepared by weighing a paste composition prepared by kneading nickel hydroxide, cobalt oxide, and a binder so as to have a predetermined weight ratio, and then kneading them. It can be produced by a method such as applying to an adhesive member and subsequently drying it, and then pressing it at a predetermined pressure. Thereafter, an alkaline storage battery can be produced by putting an alkaline aqueous solution adjusted to a predetermined concentration into a container, and further putting a positive electrode and a negative electrode into a container containing the alkaline aqueous solution.

  Hereinafter, the description of the hydrogen storage alloy electrode of the present disclosure will be continued with reference to Examples.

<Example>
(Production of hydrogen storage alloy electrode and battery)
The raw materials weighed to achieve the target composition were arc-melted and pulverized and classified (<50 μm) to obtain TiCrV alloy particles (Ti ₂₀ Cr ₁₀ V ₇₀ ) as hydrogen storage alloy particles. A Cr coating layer was uniformly formed on the surface of the TiCrV alloy particles so as to have a thickness of 10 nm by a powder sputtering method to obtain a composite alloy. Further, for the purpose of imparting charge / discharge activity, Pd was uniformly coated on the surface of the composite alloy so as to have a thickness of 10 nm by a powder sputtering method to form a Pd coating layer. The composite alloy provided with the Pd coat layer thus prepared is used as a negative electrode active material, kneaded with a conductive additive (Ni powder) and a binder, filled in foamed Ni, and then dried and roll-pressed. A hydrogen storage alloy electrode was obtained. The hydrogen storage alloy electrode produced as described above was used as the MH negative electrode, the Ni (OH) ₂ electrode was used as the counter electrode, and the battery according to the example was produced using 6M-KOH as the electrolyte.
(Charge / discharge test)
The charge / discharge conditions were 25 ° C., constant current charge / discharge, the charge termination condition was 150% of the electrode capacity, the discharge termination condition was −0.5 V vs Hg / HgO, and 30 cycles of charge / discharge were performed. The capacity retention rate was calculated from the discharge capacity after 30 cycles when the discharge capacity at the first cycle was 100%. The relationship between the number of cycles and the capacity maintenance rate is shown in FIG.

<Comparative example>
A hydrogen storage alloy electrode and a battery according to a comparative example were produced and subjected to a charge / discharge test in the same manner as in the example, except that the Cr coat layer was not formed on the surface of the TiCrV alloy particle which is a hydrogen storage alloy particle. . The results are shown in FIG.

[result]
As shown in FIG. 1, the battery according to the example manufactured by forming the Cr coat layer on the surface of the hydrogen storage alloy particles had a capacity retention rate of 78% after 30 cycles. On the other hand, the battery according to the comparative example manufactured without forming the Cr coat layer on the surface of the hydrogen storage alloy particles had a capacity retention rate of 64% after 30 cycles. Therefore, according to the present disclosure, it was confirmed that the cycle characteristics of the hydrogen storage alloy electrode can be improved by forming a Cr coat layer on the surface of the hydrogen storage alloy particles.

Claims (1)

Hydrogen storage alloy particles having a body-centered cubic structure and containing a TiCrV alloy;
A composite alloy having a Cr coating layer mainly composed of a single Cr formed on the surface of the hydrogen storage alloy particles;
Hydrogen storage alloy electrode.