Sn(78)Ge(22)@carbon core-shell nanowires as fast and high-capacity lithium storage media.

Branched Sn78Ge22@carbon core-shell nanowires were prepared by thermal annealing of butyl-capped Sn78Ge22 clusters at 600 degrees C in a vacuum. The first discharge and charge capacities are 1250 and 1107 mA h/g, showing a Coulombic efficiency of 88%. Such a one-dimensional core-shell design exploits the benefits of the Sn78Ge22 nanowire to produce an exceptional high rate lithium reactivity (93% Coulombic efficiency at 8C (=6400 mA/g) rate) as well as excellent capacity retention after extended cycles (capacity retention of 94%).