DEVELOPMENT OF AB(5) TYPE HYDROGEN STORAGE ALLOYS WITH LOW CO CONTENTFOR RECHARGEABLE NI-MH BATTERIES WITH RESPECT TO ELECTRIC VEHICLE APPLICATIONS

Rechargeable alkaline nickel-metal hydride (Ni-MH) batteries have rece ntly started to penetrate the consumer battery market. In contrast to the widely used Ni-Cd batteries they display up to 50% higher storage capacity and, due to the absence of Cd, an improved environmental comp atibility. The electrochemically active material at the negative elect rode is a hydrogen storage alloy. In most commercial applications so-c alled AB(5) alloys having a CaCu5 type crystal structure have been use d so far. These commercial AB(5) alloys are usually of the type Mm(Ni, Co,Al,Mn)(5), containing typically 10 wt% Co. Mm denotes Mischmetal, a cost-effective mixture of the rare earths La, Ce, Pr and Nd. The larg e amount of Co is added to produce an alloy with a reasonable cycle li fe, but increases the alloy cost considerably. The Ni-MH system is con sidered as a promising energy source for pure electric vehicles and hy brid cars. However for this application it is necessary to decrease th e Co content in these alloys without diminishing the cycle life endura nce. Hydrogen storage alloy production by gas atomisation represents a promising way to achieve this goal.