The subsequent charge
curve shows a capacity of 652mA h g1 up to 1.2V. Such an initial
irreversible loss of 67.1% is mainly caused by the irreversible
reduction of SnO2 to Sn and the formation of a solid electrolyte
interface (SEI) on the surface of the active materials. For the second
cycle, the non-supported SnO2 nanowire arrays exhibit a high
discharge capacity of 792mA h g1 and a charge capacity of
640mA h g1, showing a higher Coulombic efficiency of 80.8%.
However, a relatively low discharge capacity of 403mA h g1 is
retained after 60 cycles due to the volume variation, structural
degradation and aggregation of non-supported SnO2 nanowires
upon insertion/extraction of lithium ions.