We have investigated the reaction mechanisms of lithium toward Ni 3 Sn 4 in an electrochemical cell and the electrode/electrolyte interface phenomena in a combined X-ray photoelectron spectroscopy (XPS) and 119 Sn Mo ¨ssbauer spectroscopy approach, which allows a simultaneous analysis of the surface and of the bulk of the active material particles. We show that 4 mol of lithium per mole of Ni 3 Sn 4 are consumed to form the solid electrolyte interface (SEI) at the first stage of discharge. The composition and behavior of this SEI have been compared to those observed with graphite. The Li-Sn alloying process occurs in the second stage of discharge to form Li 7 Sn 2 . This mechanism is reversible and allows restoring the Ni 3 Sn 4 phase at the end of the cycle.

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