3. Sealed nickel-metal hydride battery

3.1 Introduction

Introduced in the 1980s, the sealed nickel-metal hydride battery is more recent than the previous two. It is the culmination of research carried out since 1970 on alloys capable of storing hydrogen. This led to the development of metal hydrides and the concept of the low-pressure hydrogen storage electrode. This battery is usually referred to by the symbol Ni-MH. This is an approximate name, since, as in the case of the nickel-cadmium (or nickel-iron) battery, the positive electrode is based on nickel oxyhydroxide NiOOH. The Ni-MH battery differs from the Ni-Cd battery in that its negative electrode uses hydrogen absorbed in a metal alloy instead of cadmium. Under these conditions, the behavior and characteristic curves of the two systems are comparable, and the no-load...