JPH02174063A - Hydrogen storage electrode - Google Patents

Abstract

PURPOSE:To increase both the initial electric capacity and cycle life by using an alloy with the specific composition concurrently containing Nd, Zr, Co and Al elements and constituted with part of La quantity by an Nd element and a Zr element and constituted with part of Ni quantity by a Co element and an Al element. CONSTITUTION:A hydrogen storage alloy is used for a negative. The hydrogen storage alloy is expressed by a formula La1-x-yNdxZryNiaCobAlc and concurrently contains Nd, Zr, Co and Le elements, part of La quantity is substituted by an Nd element and a Zr element, and part of Ni quantity is substituted by a Co element and an Al element. In the formula, (x), (y), (a), (b) and (c) are set to 0.10<=x<=0.20, 0.05<=y<=0.15, a+b+c=5, 3.5<=a<=4.0, 0.5<=b<=1.1, and 0.4<=c<=0.5. An hydrogen storage electrode with a large charge/discharge capacity and little characteristic deterioration after repeated charge/discharge cycles is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a nickel-hydrogen secondary battery that uses a hydrogen storage alloy as a negative electrode and a nickel oxide bridge as a positive electrode.

[Conventional technology and its issues]

In order to improve energy storage capacity, a secondary battery has been proposed that uses a hydrogen storage alloy that reversibly stores and releases hydrogen as a negative electrode, and uses the stored hydrogen as an active material, but it has a large charge/discharge capacity. In addition, a hydrogen storage alloy whose properties do not deteriorate even after repeated electrochemical hydrogen storage and desorption cycles over a long period of time, and which is inexpensive, has not yet been developed. This is because the mainstream storage alloy is based on the LaNi5 system and uses a large amount of expensive additive elements such as Co.

For example, La, which was developed by Philips, is said to have a relatively high battery charge/discharge capacity and a relatively long cycle life among the hydrogen storage alloys discovered so far.
N1z, 5coz, 4AI11.1 alloy and Lao,
5Ndo, Jig, 5(:O!, 4Sio,
+ alloys are known (Philips Journal of Research.

38S, p, 1-94.1984). These alloys contain a considerable amount of the expensive Co element in order to prevent property deterioration due to oxidation and pulverization of the alloy. ,but,
Substituting a large amount of Co element for Ni element causes a decrease in hydrogen absorption Rf, which causes loss of the feature of high energy density, which is an expected advantage of hydrogen-nickel secondary batteries.

In order to solve the above-mentioned problems, the present invention aims to provide a hydrogen storage electrode that has a large charge/discharge capacity and exhibits less deterioration in characteristics even after repeated charge/discharge cycles.

[Means for Solving the Problems] The hydrogen storage electrode according to the present invention has an alloy comprising:
Composition formula La+-x-yNd, 1ZryNiicObA1
It is represented by c and contains Nd, Zr, Co and A1 elements at the same time, part of the amount of La is Nd element and Zr element, and Ni
0.10≦χ≦0.20.0.05 in a hydrogen storage alloy characterized by replacing a part of the amount with Co element and A1 element.
≦y≦0.10, a+b+c=5.3.5≦a≦4.0
．． The above-mentioned problem was solved by setting the range of 0.5≦b≦1, 1, 0.4≦c≦0.5.

(Function) As shown in the above compositional formula as a hydrogen storage alloy, La
By using an alloy in which some of the elements are replaced with Nd and Zr elements, and some of the Ni elements are replaced with Co and A1 elements for the electrode, the alloy remains stable even after repeated use, as specifically illustrated in Examples. Since the decrease in electric capacity was small, a hydrogen storage electrode with a capacity far superior to that of conventional technology after 300 cycles could be produced. Furthermore, since this alloy has a low content of the expensive Co element, it can be provided at a lower price than alloys developed so far.

〔Example〕

Reprint purity of 99.5% or higher La, Nd, Zr,
Various hydrogen storage alloys as shown in Table 1, including alloys serving as examples of the present invention, were produced using Ni, Co+AI metals in an argon arc melting furnace. All alloys contain the A1 element, and the amount added was adjusted so that the equilibrium hydrogen dissociation pressure of the alloys was below atmospheric pressure at 60°C. After mechanically pulverizing these alloys, a copper coating layer corresponding to about 20% by weight was formed on the surface of the alloy powder by electroless plating. Next, a fluororesin (tetrafluoroethylene/fluoropropylene copolymer, resin addition amount: equivalent to 10 wt%) was added as a binder to the copper-coated C microencapsulated hydrogen storage alloy obtained in this way, and cold A molded article having a diameter of 13 mm and a weight of 300 a+H was formed by pressing. This was sandwiched between nickel meshes as current collectors from both sides, and hot-pressed at a temperature of 300° C. to produce a hydrogen storage electrode.

These hydrogen storage electrodes were used as negative electrodes, sintered nickel oxide electrodes were used as positive electrodes, and mercury oxide electrodes were used as reference electrodes.
A test battery was assembled using a 6N potassium hydroxide solution as an electrolyte. Note that all test batteries were negative electrode regulated types in which the battery capacity depends on the capacity of the negative electrode. These test batteries were placed in a constant temperature room at a temperature of 20°C, and a charging current of 4
A long-term charge/discharge cycle was conducted by charging at 0 mA for 2.5 hours, resting for 0.5 hours, and then discharging at a discharge current of 20 mA until the voltage decreased to -0.6 V with respect to the reference electrode. . Table 1 shows the results for various alloys.
Shown below.

Below are the alloys of Comparative Example 1 (LaNiz, 5coz, aAlo
, +) has a composition developed by Philips, but the initial discharge capacity is about 265 mAh/g, 30
The remaining discharge capacity after 0 cycles is about 71%.

As shown in Comparative Example 2.3, when the content of this Co element is reduced, the initial discharge capacity increases, but the capacity remaining rate decreases. Therefore, the alloy of Comparative Example 2 with half the Co element content (LaNi 3.5Co1.zAIo
, 3), when part of La was replaced with Nc1 element, as shown in Comparative Examples 4 and 5, the larger the amount of substitution, the lower the initial discharge capacity, but the cycle life improved (around Furthermore, as shown in Comparative Examples 6 and 7, when part of La was replaced with Zr element, as with Nd replacement, the initial discharge capacity decreased as the amount of substitution increased, but the cycle life decreased. Similarly, the alloy of Comparative Example 3 (LaNia, 0C60, 6AI11.a) in which the Co element content was further halved
Comparative Examples 8 and 9 are those based on 200% La based on Zr element substituted with a part of La, and although the initial discharge capacity decreased as the amount of substitution increased, the cycle life tended to improve. In this case, when comparing the substitution effects of Nd and Zr elements from the viewpoints of reducing initial discharge capacity and improving cycle life, the substitution effect of Zr element is greater than the effect of Nd element.

As shown in Comparative Examples 5 and 7, even if the amount of Co element substitution is halved from 2.4 to 1.2 in the composition formula, replacing a small portion of La element with Nd or Zr element Comparative example 1
Although we were able to achieve the same electrical capacity and cycle life as the LaN1z, 5coz, and 4AIO11-based alloys, we were unable to significantly exceed their performance.

Therefore, when part of the La element was replaced with the Nd element and the Zr element at the same time, the electrode life could be significantly improved. Each of the alloys of Examples 1, 2 and 3 was based on the composition of Comparative Example 2, in which part of the La element was replaced with the Nd element and the Zr element at the same time. The capacity retention rate of the alloys of Examples 1 and 2 is improved by 10% or more compared to the alloy of Comparative Example 7, and the alloy of Example 3 is compared to the alloy of Comparative Example 6. I understand. Further, each of the alloys of Examples 4, 5 and 6 was based on the alloy of Comparative Example 3 in which the amount of Co element substitution was further reduced in order to increase the initial discharge capacity. Although the alloy of Example 4 has a slightly lower initial discharge capacity than the alloy of Comparative Example 8, and the alloys of Examples 5 and 6 have a slightly lower initial discharge capacity than the alloy of Comparative Example 9, the cycle life is greatly improved. ing. As described above, it has been found that the cycle life, which was not sufficient when only the Zr element was substituted alone, is significantly improved by the combined substitution with the Nd element. This effect, as seen in Example 4.5.6,
It can be seen that this is noticeable in a range where the Co element content is low.

Therefore, in the case of single substitution of Nd element or Zr element, C
The amount of substitution of o element was required to be about 1.0, but Nd and Z
In the case of complex substitution of r element, it was found that a high cycle life can be obtained even if the amount of Co element substitution is lowered to about 0.5. Therefore, it was possible to obtain electrodes shown in Examples 4 and 5, which had performance superior to the electrode of Comparative Example 1 in both initial capacitance and cycle life.

〔Effect of the invention〕

In this way, N
d, Zr, Co and A1 elements at the same time, La
Part of the amount is Nd element and Zr element, and part of the Ni amount is Co.
General formula La+-x-yNdx substituted with element and A1 element
In the alloy represented by zryN+aCo, A1c, 0.
10≦x≦0.20.0.05≦y≦0.10. a+
b+c=5.3.5≦a≦4.0.0.5≦b≦1.1
．． If an alloy in the range of 0.4≦c≦0.5 is used, the decrease in capacitance will be small even after repeated use, so the capacity after 300 cycles will be the same as the conventional LaN 1g, 5cOz,
It is possible to obtain an electrode that far exceeds the performance of s-based alloys and is inexpensive, so it has high practical value.

Claims (1)

[Claims] General formula La_1_-_x_-_yNd_xZr_yNi
It is expressed as _aCo_bAl_c and contains Nd, Zr, Co and Al elements at the same time, and a part of the amount of La is Nd element and Z
A hydrogen storage alloy characterized by replacing a part of the Ni amount with Co element and A1 element with r element, and 0.10≦x≦0.
20, 0.05≦y≦0.15, a+b+c=5, 3.
5≦a≦4.0, 0.5≦b≦1.1, 0.4≦c≦0
．． A hydrogen storage electrode using an alloy shown in each range of 5.