Electrochemical properties of Ti-Ni-Sn materials predicted by 119Sn Mossbauer spectroscopy

The electrochemical activity of TiNiSn, TiNi2Sn and Ti6Sn5 compounds considered as negative electrode materials for Li-ion batteries has been predicted from the isomer shift- Hume-Rothery electronic density correlation diagram. The ternary compounds were obtained from solid-state reactions and Ti6Sn5 by ball milling. The Sn-119 Mossbauer parameters were experimentally determined and used to evaluate the Hume-Rothery electronic density [e(av)]. The values of [e(av)] are in the region of Li-rich Li-Sn alloys for Ti6Sn5 and outside this region for the ternary compounds, suggesting that the former compound is electrochemically active but not the two latter ones. Electrochemical tests were performed for these different materials confirming this prediction. The close values of [e(av)] for Ti6Sn5 and Li-rich Li-Sn alloys indicate that the observed good capacity retention could be related to small changes in the global structures during cycling.