This paper deals with new tin-based composite β-Sn/(CaSiO3)0.4 negative electrode materials for Li-ion batteries. The nature of the oxide matrix and of dispersed tin particles has been investigated by X-ray diffraction (XRD), scanning electron microscope (SEM) coupled with energy dispersion spectroscopy (EDS) and Mössbauer spectroscopy by both transmission (TMS) and backscattering (CEMS) mode for bulk and interface characterizations. The electrochemical behaviour of the composite has been studied during Li-reaction processes. Electrochemical investigation and Mössbauer data analyses suggest the formation of Li7Sn2 during Li reaction. The reversible mechanism is based on cycling between β-Sn and Li7Sn2. An interface composed of CaSnIVSiO5 and a SnII species between tin particles dispersed in the CaSiO3 matrix is responsible of the irreversible capacity observed in this composite during the first discharge.