Na–Sb–Sn ternary phase diagram at room temperature for potential anode materials in sodium-ion batteries

Abstract

A first attempt to build an experimental Na–Sb–Sn ternary phase diagram at room temperature is presented. Different compositions of NaxSbySn100-x-y were melted in sealed tantalum tubes. The powders formed are polycrystalline according to X-ray diffraction studies and their patterns were refined by Rietveld method. The ternary phase diagram Na–Sb–Sn is, at first sight, complex. We have observed unidentified stable phases which do not correspond to known phases of the individual constituents or their alloys. The unidentified phases are therefore most likely ternary. A layered-type structure was observed in the powders in which an unidentified phase was grown as major compound. The ternary phase diagram will be a useful tool to understand the possible phases formed electrochemically when SbSn alloys are used as anode materials in room temperature sodium ion batteries. Indeed, some groups have recently reported promising results of this unconventional anode electrode material, bringing to light new interest in intermetallic electrode materials for sodium ion batteries.