Nanosized Sn4P3 with a layered structure was synthesized by a mechanochemical method, and electrochemical and local structural characteristics of tin phosphide during charge/discharge were studied for its use as an anode material for lithium secondary batteries. As the amount of lithium insertion increased, tin phosphide was converted into lithium phosphides followed by lithium-tin alloy formation, which was confirmed by differential capacity plots and X-ray absorption spectroscopic (XAS) analysis. Based on X-ray diffraction, XAS, and electrochemical data, a three-step reaction mechanism of Sn4P3 with lithium was suggested. Tin phosphide showed a good cyclability and retained a fairly large capacity of 370 mAh/g up to 50 cycles when cycled within a limited voltage window. (C) 2004 The Electrochemical Society.