High aspect-ratio germanium-tin alloy nanowires: potential as highly efficient Li-ion battery anodes

Here, the fabrication of a high aspect ratio (>440) Ge_1−xSn_x nanowires with super-thin (≈9 nm) diameter, much below the Bohr radius, using a simple solvothermal-like growth method under supercritical toluene conditions at a reaction temperature of 440 °C is reported. Ge_1−xSn_x nanowires are grown with varying amounts of Sn in Ge lattice, between 3.1 to 10.2 at%. The growth of the Ge_1−xSn_x alloy nanowires is achieved without any additional catalysts, and directly on current collector substrates (titanium) for application as Li-ion battery anodes. The electrochemical performance of the binder-free Ge_1−xSn_x nanowires as an anode material for Li-ion batteries is investigated via galvanostatic cycling and detailed analysis of differential capacity plots. The dimensions of the nanowires, and the amount of Sn in Ge, are critical to achieving a high specific capacity and capacity retention. Ge_1−xSn_x nanowires with the highest aspect ratios and with the lowest Sn content (3.1 at%) demonstrate exceptional capacity retention of ≈90% and 86% from the 10th to the 100th and 150th cycles respectively, while maintaining a very high specific capacity value of 1176 and 1127 mAh g⁻¹ after the 100 and 150 cycles respectively.