Some aspects of the influence on the electrochemical mechanisms of the anion and structure in tin based negative materials are presented. Li insertion mechanisms in SnS and tin composite oxides (TCO) are analysed by 119Sn Mössbauer spectroscopy. For SnS, Mössbauer experiments were combined with in situ X-ray diffraction in order to determine tin oxidation states and identify the phases occurring during the discharge. The Mössbauer recoil-free fraction has been determined for TCO and the Debye temperature is found to be lower than that of crystalline SnO in good agreement with the lower network rigidity of the glass.