JP2828680B2 - Hydrogen storage alloy electrode - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydrogen storage alloy electrode used as a negative electrode of an alkaline secondary battery.

2. Description of the Related Art An alkaline secondary battery using a hydrogen storage alloy that reversibly stores and releases hydrogen as a negative electrode material, for example, a nickel-hydrogen secondary battery combined with a nickel positive electrode,
In recent years, research and development have been actively conducted as a new alkaline secondary battery replacing the cadmium secondary battery. Examples of the hydrogen storage alloy used for the alkaline secondary battery include rare earth-nickel alloys, magnesium-nickel alloys, and titanium-nickel alloys.
Nickel-based alloys and the like are known as typical ones.

Here, the rare earth-nickel alloy among the above alloys is
It is most excellent as a negative electrode material because it is relatively stable in an alkaline electrolyte, easy to activate, and has features such as storing and releasing hydrogen near normal temperature and normal pressure. However, there are problems such as severe pulverization accompanying hydrogen storage and release.

On the other hand, the magnesium-nickel alloy, titanium-
Nickel-based alloys and the like have a feature that the hydrogen storage amount is larger than that of the rare earth-nickel-based alloys and are hardly pulverized.However, they are easily corroded by an alkaline electrolyte or oxygen gas, and additionally activated. It has problems such as slowness.

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and is a hydrogen storage alloy electrode that is stable in an alkaline electrolyte, has a large hydrogen storage amount, and has a small amount of fine powder associated with hydrogen storage and release. The purpose is to provide.

Means for Solving the Problems To achieve the above object, the present invention provides a first alloy phase comprising an intermetallic compound having a CaCu _5- type crystal structure,
A hydrogen storage alloy electrode comprising a hydrogen storage alloy comprising a multiphase hydrogen storage alloy in which a second alloy phase comprising an intermetallic compound having a crystal structure other than CaCu ₅ type is dispersed, wherein the CaCu ₅ type crystal Intermetallic compound having a structure, Sc,
At least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd and Sm, and Cr, Mn, Fe, Co, Ni, C
u, Al and at least one element selected from the group consisting of Si, the intermetallic compound having a crystal structure other than the CaCu _5- type, comprises Mg, Ti, Zr, V, Nb and Ta At least one element selected from the group, Cr, M
n, Fe, Co, Ni, Cu, Al and at least one element selected from the group consisting of Si and capable of reversibly storing and releasing hydrogen, wherein the second The hydrogen storage alloy electrode, wherein the alloy phase is harder than the first alloy phase.

Effect In alloys cast by adding elements such as Mg, Ti, Zn or intermetallic compounds composed of these elements to the molten CaCu _5- type intermetallic compound, the metal compound having a CaCu _5- type crystal structure is An intermetallic compound phase such as Ti ₂ Ni type, MgNi type, or ZrMn ₂ type is precipitated and dispersed in the resulting alloy phase to form a multiphase structure.

In this way, if the alloy phase composed of the intermetallic compound having the CaCu _5- type crystal structure becomes the parent phase and the dissimilar intermetallic compound phase that is harder than the parent phase is dispersed, the entire alloy hardens and the mechanical strength increases. Therefore, pulverization accompanying hydrogen storage and release is suppressed.

In addition, the intermetallic compound phase based on Ti, Zr, Mg, etc. has a large hydrogen storage capacity, and the alloy phase composed of such a compound has a structure included in the alloy phase composed of CaCu ₅ type intermetallic compound. Therefore, it is protected from an atmosphere that causes corrosion such as an alkaline electrolyte and oxygen. As a result, the hydrogen storage amount of the entire alloy increases, and the charging / discharging reaction of the alloy electrode easily proceeds, so that the charging efficiency at the time of rapid charging increases.

Examples [Example I] First, a mass of commercially available Mm (Misch metal) Ni, Co, A
After weighing l, Mn, and Ti to the composition ratio shown in Table 1 [(A ₁ ) alloy], they are charged into an arc melting furnace in an inert atmosphere of argon. Next, an alloy is prepared by performing a known arc discharge process.

Next, the alloy thus prepared was mechanically pulverized into a powder having an average particle diameter of 50 μm, and 10% by weight of polytetrafluoroethylene (PTFE) powder was added as a binder to the powder. To create a paste. After this, wrap this paste in nickel mesh and
A hydrogen storage alloy electrode was obtained by pressure molding at a pressure of / cm ² . The amount of alloy contained per electrode is 1.0 g.

The electrode thus fabricated is hereinafter referred to as (A ₁ ) electrode.

Thereafter, a nickel-hydrogen battery was manufactured by combining the above electrode and a nickel positive electrode having an electrode capacity of 1000 mAh.
This test battery is an open system and the electrolyte contains 30 wt.
% KOH aqueous solution is used.

The battery fabricated in this manner is hereinafter referred to as (A ₁ ) battery.

(Examples II to XI)

An electrode and a material were prepared in the same manner as in Example I above, except that the raw materials (Cu, Zr, Mg, V, Nd, and Ta were used) and the composition ratio were changed as shown in Table 1 below. A battery using the electrode was manufactured.

The electrodes and batteries thus manufactured are hereinafter referred to as (A ₂ ) electrode to (A ₁₁ ) electrode and (A ₂ ) battery to (A ₁₁ ) battery, respectively.

(Comparative example)

An electrode and a battery using this electrode were produced in the same manner as in Example I except that Ti was not used as a raw material.

The electrode and the battery thus manufactured are hereinafter referred to as (X) electrode and (X) battery, respectively.

[Experiment I] (A ₁ ) battery using the above hydrogen storage alloy electrode of the present invention
(A ₁₁₎ cells and using a hydrogen storage alloy electrode of Comparative Example (X) Battery charge-discharge cycle test (environmental temperature: 20 ° C.) was carried out.

The test conditions were changed between 10 cycles and after 11 cycles. That is, in order to measure the electrode capacity of the hydrogen storage alloy, the first 10 cycles were performed under the conditions that the battery was charged at a charging current of 50 mA for 6 hours and then discharged at a discharging current of 50 mA until the battery voltage reached 1.0 V. On the other hand, after the eleventh cycle, the alloy was charged at a charging current of 50 mA for 2 hours and discharged at a discharging current of 50 mA until the battery voltage reached -0.2 V for the corrosion resistance acceleration test of the alloy.

Here, the electrode capacity per unit weight of the alloy of the present invention and the alloy of the comparative example in the tenth cycle is shown in Table 2 below.

As shown in Table 2 above, it is recognized that the electrode capacity per unit weight of the alloy of the present invention is increased by about 20% to about 33% as compared with the comparative alloy.

Next, the number of cycles and electrode capacity of the charge / discharge cycle test after the 11th cycle (capacity at the 10th cycle is 100%)
Is shown in FIG.

As shown in FIG. 1, in the battery (X) using the alloy of the comparative example, the decrease in the electrode capacity became remarkable from about the 30th cycle, and the electrode capacity at the 50th cycle became smaller than the electrode capacity at the 10th cycle. It is observed to drop to about 50%. On the other hand, the batteries (A ₁ ) to (A ₁₁ ) using the alloy of the present invention maintain a capacity of about 75% to about 85% of the capacity at the 10th cycle even after 100 cycles. Is admitted.

These results indicate that the battery using the alloy of the present invention has a larger electrode capacity and a longer charge / discharge cycle life than the battery using the alloy of the comparative example.

[Observation I]

After 100 cycles, the electrodes of the batteries (A ₁ ) to (A ₁₁ ) and the battery (X) were observed. As a result, it was recognized that the alloy particles of the (X) battery electrode were dropped due to pulverization. On the other hand, in the electrodes of the (A ₁ ) battery to the (A ₁₁ ) battery, no alloy particles fell off at all, and the SEM
No significant pulverization of the alloy particles was observed from the images.

(Observation II)

By EPMA, it was (A ₁₎ Alloy ~ (A ₁₁₎ structural observation of the surface of the alloy of the present invention. As a result, in the alloy of the present invention,
It was observed that the Ti-Ni-based alloy phase, the Mg-Ni-based alloy phase, and the like were dispersed in the rare earth-Ni-based alloy phase mainly composed of the CaCu type ₅ intermetallic compound and were separated.

Here, Ti-Ni-based alloys and Mg-Ni-based alloys inherently exhibit large hydrogen storage / release capabilities, but when used as electrodes in alkaline electrolytes, non-conductive oxides such as Ti and Mg on the surface Hydroxides are formed and the electrode reaction is harmed. However,
In the alloy of the present invention, such a metal phase having a large hydrogen storage amount but poor corrosion resistance is a rare earth-Ni alloy having relatively good corrosion resistance.
Since it is dispersed in the system alloy phase, it is protected from the external atmosphere. Therefore, as shown in Experiment I above, it is considered that the alloy of the present invention obtained a larger electrode capacity than the alloy of the comparative example.

In addition, the alloy of the present invention is an alloy having a multi-phase structure, and the above-mentioned precipitation dispersion hardening increases the mechanical strength of the alloy, so that pulverization accompanying hydrogen storage and release is suppressed. Therefore, as shown in Experiment I above, it is considered that the alloy of the present invention had improved charge / discharge cycle characteristics as compared with the alloy of the comparative example having a single-phase structure.

(Experiment II)

A battery (A ₁ ) using the alloy of the present invention to a battery (A ₁₁ ) and a battery (X) using the alloy of the comparative example were subjected to a quick charge test (environmental temperature: 20 ° C.). The results are shown in Table 3 below. The test conditions were as follows: a charge / discharge test was conducted in which the battery was charged for 6 hours at a charge current of 50 mA and the battery voltage was discharged to 1.0 V at a discharge current of 50 mA.
After the cycle, the battery is charged at a charging current of 200 mA for 1.2 hours, and discharged at a discharging current of 50 mA until the battery voltage reaches 1.0 V. Table 3 shows the ratio of the electrode capacity at a charging current of 200 mA when the capacity at a charging current of 50 mA is 100%.

From the Table 3, whereas also reduced by 18% discharge capacity in (X) alloy, it is recognized that (A ₁₎ only decreased by only several percent in the alloy ~ (A ₁₁₎ alloy. This is (A ₁ )
Since the alloy ~ (A ₁₁₎ alloy proceeds smoothly charging and discharging reactions compared to (X) alloy of the comparative example, charging efficiency during fast charge is considered to be due to improved.

Incidentally, the alloy according to the present invention has a crystal structure other than CaCu ₅ type alloy phase composed of CaCu ₅ type intermetallic compound, and hydrogen occlusion, the multi-phase structure intermetallic compound phase is dispersed with release capability The present invention relates to the alloys in general and is not limited to the alloys shown in the examples. Specifically, Ca
The alloy phase composed of Cu ₅ type intermetallic compound is Sc, Y, La, Ce, Pr, N
If it is composed of at least one rare earth element selected from the group consisting of d and Sm and at least one element selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Al and Si Well, the alloy phase composed of an intermetallic compound having a crystal structure other than CaCu ₅ type is at least one element selected from the group consisting of Mg, Ti, Zr, V, Nd and Ta and Cr, Mn, Fe, Co , Ni, Cu, Al
And at least one element selected from the group consisting of Si and Si.

Further, the effect of the alloy of the present invention is recognized only when the alloy has a multi-phase structure composed of a plurality of intermetallic compounds, and alloy powder composed of a single phase of each intermetallic compound is mixed. In such a case, the above effects cannot be obtained.

Furthermore, in the above embodiment, an arc melting furnace was used for alloy preparation, but a high-frequency melting furnace or the like may be used.

In addition, in the above embodiment, a lump material is used as a raw material of the alloy, but a granular material may be used. However, in this case, it is desirable to press-mold the raw material powder in order to prevent scattering of the raw material powder in the arc melting furnace.

Effect of the Invention As described above, the alloy of the present invention has a large hydrogen storage amount, is stable in an alkaline electrolyte, and has little pulverization due to hydrogen storage and release. Therefore, in the battery using the alloy of the present invention, the cycle characteristics and the rapid charging characteristics can be spattered, and its industrial value is extremely large.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the number of charge / discharge cycles and the electrode capacity of the batteries (A ₁ ) to (A ₁₁ ) of the present invention and the battery (X) of the comparative example.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Mikiro Tadokoro 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-2-12765 (JP, A) (58) Field surveyed (Int.Cl. ⁶ , DB name) H01M 4/24 H01M 4/26 H01M 4/38

Claims (1)

(57) [Claims] To 1. A first alloy phase consisting of an intermetallic compound having a crystal structure of CaCu ₅ type, the second alloy phase consisting of an intermetallic compound having a crystal structure other than CaCu ₅ type are dispersed multiphase A hydrogen storage alloy electrode comprising a hydrogen storage alloy comprising a hydrogen storage alloy having a structure, wherein the intermetallic compound having a CaCu _5- type crystal structure is a group consisting of Sc, Y, La, Ce, Pr, Nd and Sm. At least one rare earth element selected from the group consisting of Cr, Mn, Fe, Co, N
i, Cu, Al and at least one element selected from the group consisting of Si, the intermetallic compound having a crystal structure other than the CaCu _5- type, Mg, Ti, Zr, V, Nb and Ta And at least one element selected from the group consisting of Cr, Mn, Fe, Co, Ni, Cu, Al and Si, and reversible. A hydrogen storage alloy electrode, wherein the second alloy phase is harder than the first alloy phase.