JPH0466636A - Hydrogen storage alloy electrode and its manufacture - Google Patents

Abstract

PURPOSE:To improve the hydrogen occluding capacity of an electrode and, at the time of forming a battery, to attain its high capacity by manufacturing an alloy having a specified compsn. obtd. by adding V or the like to an Mm-Ni series alloy, and thereafter subjecting it to homogenizing heat treatment under prescribed conditions. CONSTITUTION:An alloy having a compsn. shown by MmNialphaVbetaAlgammaCodeltaMepsilon is manufactured; where M denotes one or more kinds of elements among Cr, Mn and Fe, and 3.5<=alpha<=4.0, 0.05<=beta<=0.2, 0.1<=gamma<=0.5, 0.3<=delta<=0.8 and 4.8<=alpha+beta+gamma+delta+epsilon<=5.2 are satisfied. The above alloy is subjected to homogenizing heat treatment in vacuum or in the atmosphere of an inert gas at 900 to 1300 deg.C. Furthermore, as the starting raw material, an Fe-V alloy is used, and as for the above M, it is preferably the element independently constituted of Fe or is the one partially consisting of Fe and the balance one or more kinds of Cr and Mn. In this way, the hydrogen storage alloy electrode improved in hydrogen occluding capacity and can attain the high capacity of a battery is obtainable.

Description

[Detailed Description of the Invention] Industrial Field of Application The present invention relates to a hydrogen storage alloy electrode that can reversibly absorb and release hydrogen electrochemically. Among these, alkaline storage batteries are expected to have high reliability and can be made smaller and lighter, so small batteries are used in various portable devices, and large ones are used for industrial purposes. Although some air electrodes and silver oxide electrodes are used as positive electrodes, in most cases nickel electrodes are used as positive electrodes.The change from the pocket type to the sintered type improves the characteristics and allows for further sealing. In addition to cadmium, other materials such as iron and hydrogen are also used as negative electrodes.Cadmium electrodes are currently the main electrodes. Nickel-metal hydride storage batteries that use metal hydrides, that is, hydrogen storage alloy electrodes, have attracted attention, and although many proposals have been made for manufacturing methods, alkaline storage batteries that use hydrogen storage alloys as negative electrodes, which reversibly absorb and release hydrogen, have attracted attention. Alloy electrodes have a higher theoretical capacity density than cadmium electrodes, and do not deform or form dendrites like zinc electrodes do. They have long lifespans, are non-polluting, and have high energy density, making them promising as negative electrodes for alkaline storage batteries. Also, as an alloy used for such hydrogen storage alloy electrodes,
Generally Ti-Ni and La (or Mm)-N
The i-series (Mm: Mitsushi Metal) multi-component alloy is well known, and the 4Ti-Ni multi-component alloy? ! A force that can be classified as an AB type (this characteristic is a force that exhibits a relatively large discharge capacity at the beginning of the charge/discharge cycle (there is a problem that it is difficult to maintain that capacity for a long time when charging and discharging are repeated). ABs type La (or Mm)-Ni multi-component alloy 41 In recent years, many developments have been made as electrode materials, and although it is considered to be a relatively powerful alloy material, there are already studies on such alloys.
For example, LnN ix (CoaMnbAl-)-(
JP-A No. 62-20245) and Ln (N is-
x-v-zMnxAl, coz) Mu (JP-A-63-
304570), however, the problems that the invention attempts to solve still remain.This alloy system also has a relatively small discharge capacity. Although it is essential to increase the capacity of the hydrogen storage alloy, the object of the present invention is to provide a hydrogen storage alloy electrode that has a larger discharge capacity and a longer life by improving the hydrogen storage alloy.

Means to solve problems The general formula of the present invention is MmNiαVβAITC.

Hydrogen storage alloy or its hydride, which is represented by δMe (M is one or more elements selected from Cr, Mn, and Fe, and whose composition ratio is specified) and has a CaCu5 type structure. A hydrogen-absorbing alloy electrode characterized in that it is characterized by the use of a hydrogen-absorbing alloy electrode, and an alloy manufacturing machine, which is characterized in that a homogenization heat treatment is performed in a vacuum or an inert gas atmosphere at a temperature of 900 to 1300°C. The hydrogen storage alloy electrode ζ is an optimization of the conventional Mm-Ni alloy, where hv is a number with a large atomic radius.By replacing or adding an optimal amount of this, the atomic radius is increased compared to the conventional alloy. As the size increases, the amount of hydrogen storage and release becomes large. Therefore, it is possible to store and release a large amount of hydrogen in terms of electrochemical charging and discharging characteristics. Can last for a period of time.

Therefore, an alkaline storage battery constructed using the hydrogen storage alloy electrode of the present invention, for example, a nickel-hydrogen storage battery (such as a nickel-hydrogen storage battery)
Compared to conventional batteries, it is possible to have higher energy density and longer life characteristics.After the alloy is prepared, it is heat-treated in a vacuum or inert gas atmosphere at a temperature of 900 to 1300 tons. The equilibrium pressure curve was obtained, and the hydrogen storage capacity was improved.
DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the present invention will be described below.

Commercially available La, Mm, Ni, V, AI,
Using metals such as Cr, Mn, Fe, and Co as raw materials, alloys having the compositions shown in the table were prepared by heating and melting them in an argon atmosphere east arc melting furnace. The alloy sample was heat treated at 1100℃ for 6 hours. Mm here is a mixture of rare earth metals.
As a composition i! La: 25-35% by weight Ce: 40-
50% by weight, Nd: 5-15% by weight, Pr: 2-10% by weight, and other soil metals and other metals: 1-5% by weight.

A part of this alloy sample was analyzed by alloy analysis such as X-ray diffraction and measurement of hydrogen absorption-release amount in a hydrogen gas atmosphere (normal P
(Hydrogen pressure) - (Composition) - Temperature (Temperature) measurement) The remaining samples are used for electrode characteristic evaluation. Sample Nos. 1 to 3 in Table 9 are examples in which the constituent elements or composition ratios are different from those of the present invention. Nos. 4 to 15 are some examples of the hydrogen storage alloy of the present invention.Results of X-ray diffraction measurements performed on the hydrogen storage alloy of the present invention after vacuum heat treatment.The alloy has a CaCu5 type 60,000 crystal structure. Also, compared to before heat treatment, the hexagonal peak became larger and sharper, so the homogeneity and crystallinity of the alloys were improved by heat treatment. To investigate hydrogen absorption-release characteristics in a hydrogen gas atmosphere? ,, P-C-T measurements were carried out.The results were as follows: Hydrogen storage alloy of the present invention (sample No.

4 to 15) are hydrogen absorption-release amount (alloy component 1
Sample No. whose hydrogen concentration per atom does not contain V
, increased by about 15% compared to sample No. 1. However, sample No. 12
In contrast, when the amount of V (β) is 0.3 or more, as in sample No. 3, the amount of hydrogen absorption and release is smaller than that of sample No. 1. In order to evaluate the electrode characteristics as a negative electrode for alkaline storage batteries, a single cell test was conducted.Alloys of samples No. 1 to 15 were ground to a particle size of 400 mesh or less, and 1g of this alloy powder and carbonyl as a conductive agent were used. 3 g of nickel powder and 0.12 g of fine polyethylene powder as a binder were thoroughly mixed and stirred, and a porous metal body made of expanded metal was placed in the center, and the plate was formed into a flat plate by pressing.
Heated at 130°C for 1 hour to melt the binder and create a hydrogen storage alloy electrode.A nickel wire lead was attached to this hydrogen storage alloy electrode to serve as a negative electrode.A sintered nickel electrode with excess capacity was used as a positive electrode, and a separator was used. using a boryamide nonwoven fabric as
X, using an aqueous potassium hydroxide solution with a specific gravity of 1.30 as the electrolyte, repeat charging and discharging at a constant current at 25°C, measure the discharge capacity in each cycle, and calculate the amount of electricity charged per gram of hydrogen storage alloy. 100mAX for 5 hours, and the discharge was carried out at 50mA per Ig (cut at a discharge potential of 0.8V).The results are shown in Figure 1. In Figure 1, the horizontal axis shows the number of charge/discharge cycles, and the vertical axis shows the 1g
The number in the figure corresponds to the sample No. in the table. Figure 1 shows that when the hydrogen storage alloy of the present invention is used, the discharge capacity is large, 0.30 to 0.32 Ah/g, and that high capacity can be maintained stably even after repeated charge/discharge cycles. Now that I know about the sealed nickel-metal hydride storage batteries constructed using these alloys, No.5 from the alloys of the present invention shown in the table. Three types of alloys No. 8 and No. 9 were selected, and each hydrogen storage alloy made into a powder of 400 mesh or less was mixed and stirred with a cold aqueous solution of carboxymethyl cellulose (CMC) to form a paste, and used as an electrode support with an average pore size of 1.50 microns. , porosity 95, thickness 1
．． Fill a 0mm foamed nickel sheet with 1
Dry at 20°C, pressurize with a roller press, coat the surface with fluororesin powder, and adjust the electrodes to 3.3 cm in width, 21 cm in length, and 0.45 mm in nail thickness. The plates were attached to two predetermined locations, and combined with the positive electrode and separator, the three layers were spirally shaped into a cylindrical shape and stored in an SC size battery case.The positive electrode at this time was a well-known foamed nickel electrode. 3.3 crrl, length 18 cm. In this case, lead plates were also attached at two places. Also, the separator was made of polypropylene non-woven fabric with hydrophilic properties. A solution of 30 g/l of lithium oxide was used. This was sealed to make a sealed battery. This battery has a positive electrode capacity limit, and the theoretical capacity is 3. 10 of each of these batteries were fabricated for OAh and evaluated using a normal charge/discharge cycle test.
(2 hour rate) to 150%, discharge is 0.2C (5 hour rate) and the final voltage is 1. Ov and L As a result of repeated charging and discharging cycles at 20°C, the actual discharge capacity of all batteries was lower than the theoretical capacity at the beginning of the cycle (
Achieves the theoretical capacity of 3゜OAh after several charging and discharging cycles.
Commercially available ferrovanadium (Fe-V alloy V: 5
0 to 90% by weight) was used to prepare alloys with the same composition as Samples No. 9, 14, and 15, and the same evaluation was performed. The same results as above were obtained. Here, the alloy composition of the present invention Explain the action of N
Since i contributes to the activity for electrochemical absorption and desorption of hydrogen, increasing the activity by increasing N1jl will increase the discharge capacity.Since Ni has a small atomic radius & increasing the amount of Ni The lattice volume decreases and the hydrogen storage capacity itself decreases. Therefore, V with a large atomic radius is
i-A I-Co-M alloy (M is Cr, Mn,
When substituted or added to the B site of one or more types of Fe (Fe), the lattice volume increases and the amount of hydrogen storage increases.In this way, V greatly contributes to increasing the amount of hydrogen storage.However, V does not interact with hydrogen. Since the affinity is very high, if there is too much V, the absorbed hydrogen will be strongly bonded to V and will not be released and will remain in the alloy. where - as an example Mm N i
*, aVxA I s, tco i, tM nl, 6
FIG. 2 shows the relationship between the amount of V and the discharge capacity at -x.

In Figure 2, the horizontal axis shows the amount of V (x) and the vertical axis shows the discharge capacity per gram of alloy.
, 2 and 3, where the V amount is 0.3 or more, the discharge capacity becomes small.In fact, the amount of hydrogen absorbed is large in the first cycle, but from the second cycle onwards, the amount of hydrogen absorbed decreases significantly. If the amount of V is smaller than 0.05, the effect of substitution or addition of V will not appear and the discharge capacity will not increase.Therefore, the optimal amount of V is 0.05≦β≦0.2. Since the balance between the amount of Ni and the amount of V is important, it must be 3.5≦α≦4.0 (℃ -4, In the P-C-T characteristic, the presence of AI causes a plateau. The presence of enhanced LAM (one or more of Cr, Mn, and Fe) reduces hysteresis, which contributes to an increase in discharge capacity.
Although the presence of co suppresses the decrease in discharge capacity due to repeated charging and discharging, too little of any of these elements will not produce any effect, and too much will reduce the amount of V and Ni.
Due to the relationship with the amount, the homogeneity of the alloy deteriorates, leading to a decrease in the amount of hydrogen storage. Therefore, 0.1≦T≦0.5 0゜3≦
δ≦0.8, 4.8≦α1β10T+δ1ε≦5.2
In order to obtain a hydrogen storage alloy electrode with high capacity and long life, it is important that the alloy contains an optimum amount of V. Effects of the Invention Since the hydrogen storage alloy electrode of the present invention contains V as a component, it has a higher discharge capacity than conventional ones. It can maintain high capacity for a long time even after repeated discharge cycles, and since the alloy is heat treated at a predetermined temperature after making the alloy, its hydrogen storage capacity is improved and when used to form a battery,
The capacity can be increased.

[Brief explanation of the drawing]

Figure 1 shows the charge/discharge cycle characteristics of various alloys, and Figure 2 shows the results of single cell tests for various alloys.
Correlation diagram between V amount and discharge capacity in @, 2com, yMns, s-x Name of agent: Patent attorney Shigetaka Awano Number of discharge cycles

Claims (3)

[Claims] (1) The general formula is MmNiαVβAlγCoδMε (where M is one or more elements selected from Cr, Mn, and Fe, and 3.5≦α≦4.0, 0.05≦β≦0.2
, 0.1≦γ≦0.5, 0.3≦δ≦0.8, 4.8≦
α+β+γ+δ+ε≦5.2), CaCu_5
A hydrogen storage alloy electrode characterized by using a hydrogen storage alloy having a mold structure or a hydride thereof. (2) The method for manufacturing a hydrogen storage alloy electrode according to claim 1, characterized in that after the alloy is prepared, a homogenization heat treatment is performed in a vacuum or an inert gas atmosphere at a temperature of 900 to 1300°C. (3) Using ferrovanadium (Fe-V alloy) as a starting material, make sure that M in the above general formula is Fe alone or partially Fe, and the remainder is one or more elements selected from Cr and Mn. A method for producing a hydrogen storage alloy electrode according to claim 1 or 2.