Confined metal Ge quantum dots in carbon nanofibers for stable rechargeable batteries.

As a promising alloy-type anode material for rechargeable batteries, the metal germanium (Ge) shows high capacity, but it suffers from a fast capacity fading problem caused by a large volume expansion during lithiation/delithiation cycles. In this study, via a facile electrospinning method, we optimized the combination structure of Ge quantum dots (QDs) and carbon nanofibers (CNFs). Specifically, Ge QDs with a diameter of 4-7 nm were highly dispersed in porous (pore size 10-150 nm) CNFs. The hybridized Ge/CNF nanocomposite exhibited remarkable Li storage performances such as high reversible capacity (1204 mA h g-1 at a current density of 200 mA g-1), high capacity retention (87.1% after 100 cycles) and excellent rate property (760 mA h g-1 at 3000 mA g-1). The improved electrochemical performance was due to the synergistic effects of Ge QDs and carbon nanofibers; this effectively alleviated the volume expansion problem, prevented the agglomeration of Ge, maintained the structural stability of the nanocomposite, and improved the electrode kinetics of diffusion of Li ions.