Analysis of the Activation Mechanism of Hydrogen Storage Alloy Negative Electrodes Modified by Nickel Particles

Shinya MORISHITA*, Hiroshi FUKASAKU, Yutaka OHYA, Yasuhito KONDO, Shin-ichi TOWATA and Katsushi ABE

Toyota Central Research and Development Laboratories, Inc.; 41-1 Yokomichi, Nagakute, Aichi 480-1192 Japan
Toyoda Automatic Loom Works, Ltd.; 2-1 Toyoda-cho, Kariya-shi 448-8671 Japan

In the case of Ni-MH batteries using fine nickel particles-added hydrogen storage alloy negative electrodes, the initial activation of the negative electrodes was promoted. From electrochemical impedance analysis of the negative electrodes and specific surface area and oxygen content measurement of the added fine nickel particles, the mechanism of this phenomenon was presumed to be as follows:
1) Minute rough parts on the surface of the nickel particle act as active sites for charge/discharge reactions. Rapid hydrogen transfer takes place between the active sites and the hydrogen storage alloy.
2) Pulverization of the alloy occurs due to the hydrogen absorption into the alloy, and new active sites are formed on the alloy surface.
3) Therefore, the initial activation of the negative electrode is promoted by addition of the fine nickel particles.

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