Mössbauer spectra as a “fingerprint” in tin–lithium compounds: Applications to Li-ion batteries

Several Li–Sn crystalline phases, i.e. Li2Sn5, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2 and Li22Sn5 were prepared by ball-milling and characterized by X-ray powder diffraction and 119Sn Mössbauer spectroscopy. The analysis of the Mössbauer hyperfine parameters, i.e. isomer shift (δ) and quadrupole splitting (Δ), made it possible to define two types of Li–Sn compounds: the Sn-richest compounds (Li2Sn5, LiSn) and the Li-richest compounds (Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2, Li22Sn5). The isomer shift values ranged from 2.56 to 2.38 mm s−1 for Li2Sn5, LiSn and from 2.07 to 1.83 mm s−1 for Li7Sn3, Li5Sn2, Li13Sn5, Li7Sn2 and Li22Sn5, respectively. A Δ−δ correlation diagram is introduced in order to identify the different phases observed during the electrochemical process of new Sn-based materials. This approach is illustrated by the identification of the phases obtained at the end of the first discharge of η-Cu6Sn5 and SnB0.6P0.4O2.9.