Unlike bulk Si, the
recovered nano-Si has high functionality due to the small size and
porous nature. It exhibits excellent electrochemical behavior without
any further coating or modification (Fig. 4). Upon deep galvanostatic
cycling between 0.01 and 1 V, the discharge (delithiation) capacity
reaches 2790 mA h g21 for the first cycle at C/50 and stabilizes
around 1750 mA h g21 for later cycles at C/2 (Fig. 4a); these values
are seven and five times the theoretical capacity of graphite (372 mA
h g21). The cycling stability is excellent as well. No capacity decay was
observed over the 150 cycles after the initial lower-current cycles, and
the capacity retention values after 200 and 300 cycles are 95% and
86%, respectively. The voltage profiles for the different cycles are
shown in Supplementary Fig. S9. The similarity of the profiles over
300 cycles indicates highly reversible Li insertion and extraction.