▎ 摘　　要

GeO2-reduced graphene oxide (RGO) composites were prepared by a simple freeze-drying method. After thermal annealing in N-2 atmosphere at 450 degrees C for 2 hours, the composites were examined as anode materials of sodium ion batteries for the first time. Their morphology, structure and electrochemical performance were characterized by field-emission scanning electron microscopy, X-ray diffraction, N-2 adsorption-desorption isotherm, cyclic voltammetry and electrochemical impedance spectroscopy, respectively. A maximum specific capacity of 330 mAh g (1) can be achieved after 50 galvanostatic charge-discharge cycles at a current density of 100 mA g (1) by tuning the RGO content in the composites. Even after 650 cycles at a high current density of 1 A g (1), the specific capacity can still maintain at 153.7 mAh g (1), demonstrating the excellent Na ion storage properties of the GeO2-RGO composites. (C) 2015 Elsevier Ltd. All rights reserved.