In order to study the effect of oxidation on anode material for Li-ion secondary battery, non-stoichiometric silicon oxide nanoparticles are synthesized using inductively coupled plasma (13.56 MHz). The chemical compositions and size distribution of the generated nanoparticles are measured with EDS and SMPS (Scanning Mobility Particle Sizer). The chemical composition of the nanoparticles was very similar with that of a non-stoichiometric silicon oxide film. For Li-ion secondary battery, it is recommended that the oxygen concentration should be reduced below 18 at.%. It is also revealed that pitch coating was a good method for preventing the natural oxidation and improving capacity. (C) 2010 Elsevier B.V. All rights reserved.