Ultralong germanium nanotubes (Ge NTs; see picture) are synthesized in high yield from core-shell Ge-Sb nanowires by utilizing the Kirkendall effect at 700 °C. The Ge NTs have an exceptionally high rate capability (40 Ag -1) while maintaining a reversible capacity of more than 1000 mAhg -1 over 400 cycles, with minimal capacity fading when paired with a LiCoO 2 cathode in a lithium-ion cell.