Synthesis and electrochemical properties of lithium-electroactive surface-stabilized silicon quantum dots

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 °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 °C, had the same particle size (5 nm) as n-Si annealed at 700 °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 °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 that prohibited n-Si aggregation during cycling.