[en] Composite Si/SiO_z nanoparticles have been produced from SiO powder feedstock by pulse-modulated plasma flash evaporation (PFE) and the effect on the lithium-ion battery properties are analyzed. With the introduction of power and powder-feeding pulse-modulation during PFE, the primary SiO_x particle size decreases from 27.9 to 14.3 nm and the core crystalline Si is reduced from 14.2 to 7.3 nm. Although no appreciable reduction in the overall oxygen content (x) in the SiO_x representation is confirmed, the composite nanoparticles with amorphous Si core are formed by the modulation due to the disproportionation reaction at lower temperatures. As a result, the coulombic efficiency is improved, and the higher cycle capacities are attained for the battery using the modulated nanoparticles as an anode. (paper)