Sn-substituted LaNi{sub 5} alloys for metal hydride electrodes

Abstract

This research examines the efficacy of tin additions to LaNi{sub 5} in improving the hydrogen storage capacity of the material during charging/discharging. Alloys were prepared using high energy ball milling (mechanical alloying), a technique superior to arc casting for alloying elements with a wide disparity in melting points. Characterization by X-ray diffraction and Rietveld analysis shows that tin preferentially occupies the Ni(3g) sites in the LaNi{sub 5} structure, and the unit cell volume increases linearly with tin content to the maximum tin solubility of 7.33 atomic percent (LaNi{sub 4.56}Sn{sub 0.44}). The authors found that powders prepared by mechanical alloying and not exposed to air require no activation to induce hydrogen absorption. The hydrogen storage capacity in the gas and electrochemical phase was measured as a function of tin content. They found that with increasing tin, the plateau pressure decreases logarithmically, whereas the hydrogen storage capacity decreases linearly.