Directly grown germanium nanowires from stainless steel: high-performing anodes for Li-ion batteries

Germanium (Ge) nanowires were fabricated directly on stainless steel current collectors for Li-ion batteries without any additional catalytic seeds. Substrates of stainless steel are unconventional materials for the direct growth of nanowires for battery applications. Stainless steel substrates were activated for nanowire growth by annealing them in air at a temperature of 450 °C to form a catalytic iron oxide surface layer. Large yields of Ge nanowires were obtained from oxidized stainless steel via a liquid injection chemical vapor deposition process, with diphenylgermane (DPG) as a Ge precursor. Fabricated Ge nanowires have uniform morphology and are single-crystalline. The capacity retention from a nanowire anode tested at 0.2 C is very stable, highlighted by reversible capacities of ∼1014 and 894 mAh/g after the 50th and 250th cycles, respectively. The large specific capacity values are one of the highest achieved for binder-free Ge nanomaterial-based anode materials. The high specific capacity values, good capacity retention, and voltage stability observed resulted from the excellent adhesion of the nanowires to the stainless steel current collectors, ensuring good electrical contact and electrical conductivity. Achieving such electrochemical performance from Ge nanowires grown via a significantly simplified direct growth process on a functional conductive substrate demonstrates the potential of directly grown Ge nanowires as a high-performing anode material for Li-ion batteries.