High-capacity CVD-grown Ge nanowire anodes for lithium-ion batteries: simple chemical etching approach for oxide removal

We demonstrated high-performance Ge nanowire (NWs) anodes for rechargeable lithium-ion batteries with high-capacity and high coulombic efficiency. The NWs were prepared using a simple chemical vapor deposition (CVD) method, which is favorable for the mass production of electrodes. The unstable oxides of Ge deteriorate the electrochemical characteristics of the batteries made from Ge-based anodes. To resolve the issue of the oxides and enhance the electrochemical performance, the oxides of the NWs were removed efficiently by a simple wet chemical etching method via a 10% HCl (aq) treatment. Transmission electron microscopy and energy-dispersive X-ray spectroscopy elemental mapping verified the removal of oxides. Charge and discharge capacity of the pristine NWs were 833.803 mAhg⁻¹ and 650.63 mAhg⁻¹ at first cycle. In comparison, the charge and discharge capacities after oxide removal were 1064.1 mAhg⁻¹ and 905.6 mAhg⁻¹ under the same conditions. The discharge capacity and coulombic efficiency of the oxide-removed NWs were 39.2% and 7.1% higher than those achieved without oxide removal. The coulombic efficiency of the oxide-removed NWs was higher than that of the pristine NWs (7.1% increase). The NWs were stable over 25 cycles at different C-rates. This approach provides an efficient and practical way to resolve the oxide issue of Ge-based anodes, and high-performance lithium-ion batteries were demonstrated using the oxide-removed NW anodes. This study presents an advance towards the realization of the commercial batteries based on Ge as an active electrode material.