JPS6355862A - Hydrogen-adsorptive electrode - Google Patents

Abstract

PURPOSE:To increase mechanical strength and extend a charging and discharging cycle life by adding conductive whiskers in a hydrogen-absorptive alloy or a hydride. CONSTITUTION:Conductive whickers are contained at least in a hydrogen- absorptive alloy or a hydride, wherein conductive whiskers are composed of potassium titanate (K2O.nTiO2) and the content of conductive whiskers is preferably 5-20 wt%. With the arrangement, the hydrogen-absorptive alloy particles, fluororesin fibers and conductive whickers are effectively entangled, resulting in an improvement of mechanical strength of the electrode itself and a long life is obtained by reducing the falling of the hydrogen-absorptive alloy because of a small expansion degree in repeated charging and discharging cycle and flexibility of the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to improvements in hydrogen storage electrodes used in alkaline storage batteries.

BACKGROUND ART Conventionally, hydrogen storage electrodes made of hydrogen storage alloys or hydrides of this kind have been used as negative electrodes of alkaline storage batteries because they can electrochemically store and release hydrogen. This hydrogen storage electrode has low mechanical strength, and when it is repeatedly charged and discharged, the electrode itself expands and cracks occur. Therefore, in order to solve these problems, some proposals include adding a binder to increase the bonding force between particles (Japanese Unexamined Patent Application Publication No. 1989-1992).
3-103541).

Problems to be Solved by the Invention In such a conventional structure, the bonding force between the hydrogen storage alloy particles is weak, and it is difficult to prevent cracks and falling-off phenomena that occur due to the expansion of the electrode itself due to repeated charging and discharging cycles. That's difficult. This phenomenon has the problem of increasing the internal resistance of the electrode and decreasing the amount of active material, resulting in a decrease in capacity and a shortened cycle life.

The present invention is intended to solve these problems, and aims to increase the mechanical strength of the electrode without reducing its conductivity, thereby extending the charge/discharge cycle life.

Means for Solving the Problem In order to solve this problem, the present invention includes at least a conductive whisker in the hydrogen storage alloy or hydride, and the conductive whisker is made of potassium titanate (K2O).
・nTio2), which aims to extend the lifespan by increasing the mechanical strength of the electrode itself.

Function: With this structure, the hydrogen storage alloy or hydride powder and the conductive whiskers forming fine fibers are intertwined and bonded, so these fibers reduce the expansion of the electrode itself and increase its strength. The aim is to increase the number of employees.

The details will be explained below using examples.

Example Commercially available La, Ni, and Go were weighed and mixed to a constant composition ratio, and heated and melted by an arc melting method. - As an example, the alloy composition is La. Nis, 5C
O15 was selected and used as a hydrogen storage electrode for the negative electrode. This hydrogen storage alloy is made into a fine powder of 38 μm or less using a ball mill, etc., an appropriate amount of fluororesin dispersion and conductive whiskers are mixed into a paste, and this paste is applied to both sides of the punched metal that is the current collector. After getting dressed,
It was pressurized and dried to form an electrode. Further, if necessary, the alloy can be used in the form of a hydride. In this example, the conductive whiskers used were Dentol BK-200 (trade name),
Fibrous potassium titanate (commercially available as 300 etc.)
K2O・nTi0□) was used. The average length of this fiber is 10-20 μm, and the average diameter is 0.2-0.5 μm.
It is m.

The alkaline storage battery used in this negative electrode cycle life test is shown in FIG. In FIG. 1, 1 is a negative electrode made of a hydrogen storage alloy, 2 is a sintered nickel oxide positive electrode, 3 is a separator, 4 is an alkaline electrolyte, 5 is a liquid pouring plug, and 6 is an electric plug. Hydrogen storage alloy 10y- (equivalent to 2.6mmh)
The conductive whiskers were added in different amounts.

Then, in order to understand the cycle life of the negative electrode, the positive electrode capacity was made larger than the negative electrode capacity, and the negative electrode rule was adopted. The battery charging/discharging conditions are 7.5 hours (150%
(charged) and discharged at 500m&. A comparison was made with a conventional battery using a negative electrode without conductive whiskers.

The results are shown in FIGS. 2 and 3. Figure 2 shows the results of measuring the amount of conductive whiskers added and the discharge capacity after 50 cycles. is within an appropriate range. If it is less than 5% by weight, there is little effect of increasing the mechanical strength of the electrode, and if it is more than 20% by weight, the density of the electrode itself becomes smaller, and the strength becomes weaker, and the effective amount of hydrogen per unit weight of the electrode decreases. Therefore, the discharge capacity also decreases. Therefore, from the viewpoint of performance such as extension of cycle life, the optimum addition amount is 5 to 20% by weight.

Furthermore, within this range, as an example, a cycle life test was conducted on a battery using the negative electrode of the present invention with an additive amount of 1° by weight, and the results are shown in Figure 3 in comparison with a battery using a conventional negative electrode. . In FIG. 3, in the battery using the conventional negative electrode, the capacity after 50 cycles has decreased to 70% of the initial capacity. In contrast, the battery using the negative electrode of the present invention maintains a capacity of 96 cm even after 50 cycles. Furthermore, since the capacity was 83% after 100 cycles, the cycle life was significantly improved.

By using fibrous fluororesin as the binder, the hydrogen storage alloy particles, fluororesin fibers, and conductive whiskers are effectively intertwined, improving the mechanical strength of the electrode itself and improving charging and It is thought that the degree of expansion is small even after repeated discharge cycles, and due to its flexibility, there is less chance of the hydrogen storage alloy falling off, resulting in a longer life.

Further, in this embodiment, a punched metal was used as the current collector, but if a foamed nickel porous body is used, the effect of the lattice will be even higher.

Effects of the Invention As described above, the present invention has the effect of providing a hydrogen storage electrode with a long charge/discharge cycle life.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view showing the structure of an alkaline storage battery used in an example of the present invention, Figure 2 is a diagram showing the capacity after 50 cycles depending on the amount of conductive whiskers added, and Figure 3 is a negative electrode of the present invention. FIG. 3 is a diagram comparing the cycle life of a battery using a conventional negative electrode and a battery using a conventional negative electrode. 1...Negative electrode, 2...Positive electrode, 3...
...Separator, 4...Alkaline electrolyte, 6.
...Filling tap, 6...Let's turn it on. Name of agent: Patent attorney Toshio Nakao and one other name
1 Figure 1- Negative 4-2
-Correct 4 Worries Figure 2

Claims (3)

[Claims] (1) A hydrogen storage electrode characterized in that a hydrogen storage alloy or hydride contains at least conductive whiskers. (2) The conductive whisker contained in the hydrogen storage alloy or hydride is potassium titanate (K_2O・nTiO_2)
The hydrogen storage electrode according to claim 1, characterized in that it consists of: (3) The hydrogen storage electrode according to claim 1, wherein the content of conductive whiskers is 5 to 20% by weight.