Cycle Life and Failure in the Nickel-Metal Hydride Battery

Nickel-metal hydride cells use AB₅, AB₂, AB, and A₂B compounds for the negative electrode. These intermetallic compounds differ in the ease with which they are activated and their kinetics in forming the hydride phase. Various techniques are used to optimize the storage capacities of these different classes of materials. Long cycle lives are difficult to attain primarily due to surface oxidation and the large expansion of the intermetallic lattice caused by the formation of the hydride phase. This article reviews the different failure modes active in intermetallic hydrides and the recent ways researchers have tried to increase the cycle life.