Ni3Sn4 Electrodes for Li-Ion Batteries: Li−Sn Alloying Process and Electrode/Electrolyte Interface Phenomena

We have investigated the reaction mechanisms of lithium toward Ni3Sn4 in an electrochemical cell and the electrode/electrolyte interface phenomena in a combined X-ray photoelectron spectroscopy (XPS) and 119Sn Mössbauer 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 Ni3Sn4 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 Li7Sn2. This mechanism is reversible and allows restoring the Ni3Sn4 phase at the end of the cycle.