Colloidal Tin-Germanium Nanorods and Their Li-Ion Storage Properties

Abstract

We report a facile colloidal synthesis of tin–germanium (Sn–Ge) heterostructures in the form of nanorods with a small aspect ratio of 1.5–3 and a length smaller than 50 nm. In the two-step synthesis, presynthesized Sn nanoparticles act as a low-melting-point catalyst for decomposing the Ge precursor, bis[bis(trimethylsilyl)amido]Ge(II), and for crystallization of Ge via solution–liquid–solid growth mechanism. Creation of such Sn–Ge nanoheterodimers can serve as a well-controlled method of mixing these nearly immiscible chemical elements for the purpose of obtaining Sn–Ge nanocomposite electrodes for high-energy density Li-ion batteries. Comparable mass content of Sn and Ge leads to synergistic effects in electrochemical performance: high charge storage capacity above 1000 mAh g–1 at a relatively high current density of 1 A g–1 is due to high theoretical capacity of Ge, while high rate capability is presumably caused by the enhancement of electronic transport by metallic Sn. At a current density of 4 A g–1, Sn–Ge nanocomposite electrodes retain up to 80% of the capacity obtained at a lower current density of 0.2 A g–1. Temporally separated lithiation of both elements, Sn and Ge, at different electrochemical potentials is proposed as a main factor for the overall improvement of the cycling stability.