Core–shell structured nano-Si/C (n-Si/C) anode material for Li ion batteries was prepared by substrate induced coagulation (SIC) method with nano-Si (n-Si) as core component and amorphous carbon as shell. The electronic conducting amorphous carbon shell of 5–10nm thickness which connected each n-Si particle like frog spawn shape not only buffered volume expansion of Si particles during the cycling but also acted as an electrical conducting pathway. This n-Si/C core–shell structured electrode showed a highly reversible capacity c.a. 1800mAhg−1 over 50 cycles, superior rate capability and good cycle retention.