The cycling stability and the surface passivation qualities of a heterogeneous polycrystalline NiSi2/amorphous NixSiOy core-shell nanowires cycled in a Li ion half cell is reported. The nanowire morphology showed stable cycling and excellent charge rate capability having a stable capacity above 1700 mAh/g when cycled in a coin cell at 1/2 C and retaining a capacity of 300 mAhr/g when cycled at a 10 C charge rate. It is shown that the stable cycling is due to the passivation qualities of the oxide components within the amorphous shell which create a stable solid-electrolyte interphase (SEI) during charging which is reduced during discharging through the conductive pathway provided by the Ni doping in the shell and NiSi2 in the core. The NiSi2 core interacts with Li through intercalation retaining its rigid core even while Li charged, the overall dimensions of the structure mitigate any pulverization issues, and the conductive core along with the Ni doping disallow any Li trapping leading to high columbic efficiency. (C) 2014 The Electrochemical Society. All rights reserved.