Abstract: Highly pure silicon nano-particles were synthesized by DC arc plasma evaporation.The nanostructures and properties of Si nanoparticles were characterized with X-ray diffraction, X-ray fluorescence analysis, nitrogen-oxygen determinator, and transmission electron microscopy.The influence of the ultrasonic mixing time and dispersant type on the aquatic dispersion behavior was investigated.The results show that the purity of spherical Si nano-particle with narrow size distribution was 99.93%, and the ultrasonic time, dispersant type and concentration had a major impact.For example, cetyltrime thylammonium bromide (CTAB) works best; as the ultrasonic time and CTAB-concentration increased, the dispersion was improved in an increase-stable mode.The optimized conditions included:pH value of 6, CTAB-content of 4%, ultrasonic power of 560 W and ultrasonic time of 80 min.The ultrasonic mixing and dispersant modification of Si nanoparticles increased the 1 st-discharge capacity by 14.93% (to 2640 m Ah/g) and the 1^st-coulombic efficiency to 34.92%.