In situ neutron powder diffraction study of phase-structural transformations in the La–Mg–Ni battery anode alloy

Abstract

This work was focused on studies of temperature-induced phase-structural transformations in the as-cast La2MgNi9 metal hydride battery electrode alloy. The interactions in the alloy were studied by in situ neutron powder diffraction at temperatures ranging from 300 K to 1273 K. Initial alloy is multi-phase structured, containing six different intermetallics with five stoichiometric compositions. These include the targeted rhombohedral La2MgNi9 as the main phase constituent, together with three electrochemically active intermetallics, La3MgNi14 (3R), La4MgNi19 (2H) and La4MgNi19 (3R). Furthermore, the alloy contained two “ballast” intermetallics, LaNi5 and LaMgNi4. Various transformations take place on heating, leading to the significant changes in the contents of the constituent intermetallics, first of all to the disappearance of LaNi5 and LaMgNi4. Thermal volume expansions of the studied intermetallics were well fitted by the linear dependences and resulted in similar values of 4.3–5.5 vol.% at 1223 K as compared to 300 K.