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(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-3 5) were evaluated as additive materials for the AB2 and AB5-type alloy s. Experiments were conducted to determine the optimum (i) amount of h ydride material in the electrode, (ii) ratio of the amount of hydride material to that of electronically conducting material (carbon or acet ylene black), and (iii) percentage of Teflon in the metal hydride elec trode. The discharge capacity and cycle life depended on both the type and amount of the additive material. The Teflonized carbon additive i ncreased and stability of the electrode over that of an electrode with copper powder as the additive. The increase in stability and cycle li fe is attributed to the flexible, electronically conducting three-dime nsional carbon-Teflon network which permits its intimate and stable co ntact with the active alloy particles. The additive Vulcan-XC-72 enhan ces the capacity of the electrode above that of an electrode with acet ylene black or copper. The behavior of the electrodes, in respect to t he effect of the additives, were similar with the AB2 and AB5 alloys a s active materials.