Amorphous-Si@SiO x /C composites with amorphous Si particles as core and coated with a double layer of SiO x and carbon are prepared by ball-milling crystal micron-sized silicon powders and carbonization of the citric acid intruded in the ball-milled Si. Different ratios of Si to citric acid are used in order to optimize the electrochemical performance. It is found that SiO x exists naturally at the surfaces of raw Si particles and its content increases to ca. 24 wt.% after ball-milling. With an optimized Si to citric acid weight ratio of 1/2.5, corresponding to 8.4 wt.% C in the composite, a thin carbon layer is coated on the surfaces of a-Si@SiO x particles, moreover, floc-like carbon also forms and connects the carbon coated a-Si@SiO x particles. The composite provides a capacity of 1450 mA h g−1 after 100 cycles at a current density of 100 mA g1, and a capacity of 1230 mA h g−1 after 100 cycles at 500 mA g1 as anode material for lithium-ion batteries. Effects of ball-milling and the addition of citric acid on the microstructure and electrochemical properties of the composites are revealed and the mechanism of the improvement in electrochemical properties is discussed.