Highly lithium-electroactive Si quantum dots (n-Si), coated with an amorphous carbon layer, were prepared by of butyl-capped Si annealing at 700 or 900 degrees C. The ordering of the carbon layer structure increased with increasing annealing temperature while the thickness decreased to 1 from 2 nm due to the increased ordering of carbon. n-Si, annealed at 900 degrees C, had the same particle size (5 nm) as n-Si annealed at 700 degrees C. In contrast to Si nanocrystals with an average particle size of 30 nm that had a first charge capacity of 225 mAh/g with a very small coulombic efficiency of 4%, n-Si that annealed at 900 degrees C possessed a first charge capacity of 1257 mAh/g with a significantly enhanced coulombic efficiency of 71 %. This improvement was due to the uniform distribution of n-Si with a carbon layer prohibited n-Si aggregation during cycle. (c) Elsever Ltd. All rights reserved.