Study on Nitrogenation Reaction Mechanism in Li–Sn Alloy by Observation of Microstructural Change

In this study, we focused on ammonia synthesis using Li-Sn alloys and investigated the reaction mechanism by microstructural analysis using bulk Li-Sn alloys. The nitrogenation reaction results in the formation of lithium nitride at the surface. The EDS results show that nitrogen atoms are present in the surface phase and that the concentration of Sn atoms decreases toward the surface. These results indicate that nitrogen atoms do not penetrate the bulk Li-Sn alloys. In other words, the surface phase of lithium nitride grows by outward diffusion of lithium atoms from the matrix rather than by internal penetration of nitrogen atoms. Furthermore, the activation energy of the reaction was calculated from Arrhenius plots of the growth rate of the surface phase of lithium nitride. Consequently, it was found that the nitrogenation reaction proceeds by diffusion of Li atoms in the matrix and surface phase and that Li diffusion in the surface phase is the rate-limiting step in the reaction.