X-ray diffraction, 7Li MAS NMR spectroscopy, and 119Sn Mossbauer spectroscopy study of SnSb-based electrode materials

Sn-119 Mossbauer spectroscopy is used in combination with Li-7 MAS NMR spectroscopy and X-ray diffraction to resolve the details of the different Li-Sn and Li-Sb intermetallics formed during the electrochemical reactions of nominal "SnSb" compounds inside a lithium battery. At a Li/SnSb ratio of 2.02, the Mossbauer spectrum indicates that the initial structure of the compounds are not deeply affected during the first steps of discharging. At 4.95 Li/SnSb, each spectrum consists of three components. The hyperfine parameters agree well with those of beta-Sn and a LiSn-related solid. At 7.27 Li/SnSb, the spectra reveal that no metallic Sn is present. During cell charging, the appearance of a poorly crystalline Li13Sn5 phase is detected at 8.9 Li/SnSb. NMR data show signals resulting from ionic Li of the passivating layer and from Li-Sn and Li-Sb intermetallics at downfield and upfield shifts, respectively, which depart from those observed in bulk solids. The partial recovery of the stistaite structure at the end of charging is confirmed in SnSb single-phase electrodes, whereas the opposite is true for mixtures of tin and antimony.