Interfacial reactions of Sn during initial cycling in 1 M LiPF6/EC:DMC (1:1) were studied by characterizing the surface species formed on thin film electrodes of Sn, prepared with a pulsed laser deposition, using ex-situ ATR FTIR spectroscopy and microscopy. FTIR analyses indicated that at high voltage region above 1.0 V vs. Li/Li+ the surface of Sn electrode was covered by PF-containing inorganic species probably by the interfacial reactions between Sn and PF6- anions. With charging to 0.63 V low amounted organic species with carboxylate metal salt and alkyl functionalities appeared, due to the reductive decomposition of organic solvents. The organic surface species however were destroyed upon a deep charge to 0.1 V and reproduced on the subsequent discharge process, whereas P-F containing inorganic species remained preserved. No sustainment of organic surface species but the stable passivation of Sn surface by PF-containing species during initial cycling are believed to cause unstable interfacial structure and the possibility of reduced utilization of active Sn, respectively, resulting in the large initial irreversible capacity loss. (C) 2008 Elsevier B.V. All rights reserved.