Optimization of composition and structure of metal-hydride electrodes

This paper focuses on investigations to improve the capacity and cycle-life of a Ni/MH[sub x] battery by optimization of the composition (active material and additive) and structure of the metal hydride electrode. Teflonized carbons, Vulcan-XC-72, Notrit-NK, and acetylene black (XC-35) were evaluated as additive materials for the AB[sub 2] and AB[sub 5]-type alloys. Experiments were conducted to determine the optimum (1) amount of hydride material in the electrode, (2) ratio of the amount of hydride material to that of electronically conducting material (carbon or acetylene black), and (3) percentage of Teflon in the metal hydride electrode. The discharge capacity and cycle life depended on both the type and amount of the additive material. The Teflonized carbon additive increased the stability of the electrode over that of an electrode with copper powder as the additive. The increase in stability and cycle life is attributed to the flexible, electronically conducting three-dimensional carbon-Teflon network which permits its intimate and stable contact with the active alloy particles. The additive Vulcan-XC-72 enhances the capacity of the electrode above that of an electrode with acetylene black or copper. The behavior of the electrodes, in respect to the effect of the additives, were similar with the AB[sub 2] and AB[sub 5] alloys as active materials.