The electrochemical reaction mechanism of the Sn-(CaSiO3)(0.4) composite electrode with Li was investigated by electrochemical tests and a variety of spectroscopic techniques. The electrochemical behavior of this material showed a highly reversible reaction with Li after the first discharge with a specific capacity of 530 mAh g(-1) at C/10 rate. Some essential steps of the mechanism have been inferred from Sn-119-Mossbauer spectroscopy and the electrochemical potential curve. The composite material contains three tin based phases with different tin oxidation numbers: an amorphous Sn-II phase which is reduced into Sn-0 as the first step of the discharge, (CaSnSiO5)-Si-IV and beta-Sn which are progressively transformed into lithium-tin alloys during the discharge. A Mossbauer spectrum recorded at the end of the discharge reveals the formation of Li7Sn2. The de-alloying reaction of Li7Sn2 leads to the formation of beta-Sn at the end of the charge. X-ray absorption and Sn-119 Mossbauer spectroscopy revealed furthermore that the electrochemical reaction between Li and the Sn-(CaSiO3)(0.4) composite is accompanied by an electron transfer between Li and Sn. (C) 2011 Elsevier B.V. All rights reserved.