A synthesis method consisting of a mechanical ball milling activation process followed by a sintering heating treatment is proposed to obtain MnSn2 as anode material for Li-ion batteries. This two-step approach strongly reduces the amount of βSn impurities and provides a better material morphology. This improves the electrochemical performances, even at high C-rate, as shown from the comparison between electrode materials obtained with and without this preliminary activation process. The electrochemical reactions have been followed at the atomic scale by in situ 119Sn Mössbauer spectroscopy. The first discharge is a restructuring step that transforms the pristine material into Mn/Li7Sn2 nanocomposite which should be considered as the real starting material for cycling. The delithiation of this nanocomposite is characterized by two plateaus of potential attributed to the de-alloying of Li7Sn2 followed by the back reaction of Mn with poorly lithiated Li x Sn alloys, respectively. The composition and the stability of the solid electrolyte interphase were characterized by X-ray photoelectron spectroscopy.