  For a successful integration of silicon in high-capacity anodes of Li-ion
batteries, its intrinsic capacity decay on cycling due to severe volume
swelling should be minimized. In this work, Ni-Sn intermetallics are studied as
buffering matrix during reversible lithiation of Si-based anodes. Si/Ni-Sn
composites have been synthetized by mechanical milling using C and Al as
process control agents. Ni3Sn4, Ni3Sn2 intermetallics and their bi-phasic
mixture were used as constituents of the buffering matrix. The structure,
composition and morphology of the composites have been analyzed by X-ray
diffraction (XRD), 119Sn Transmission M\"ossbauer Spectroscopy (TMS) and
scanning electron microscopy (SEM). They consist of ~ 150 nm Si nanoparticles
embedded in a multi-phase matrix, the nanostructuration of which improves on
increasing the Ni3Sn4 amount. The electrochemical properties of the composites
were analyzed by galvanostatic cycling in half-cells. Best results for
practical applications are found for the bi-phasic matrix Ni3Sn4-Ni3Sn2 in
which Ni3Sn4 is electrochemically active while Ni3Sn2 is inactive. Low capacity
loss, 0.04 %/cycle, and high coulombic efficiency, 99.6%, were obtained over
200 cycles while maintaining a high reversible capacity above 500 mAh/g at
moderate regime C/5
