▎ 摘　　要

Rechargeable magnesium (Mg) batteries have attracted research attention as one promising alternative for energy storage because of abundant raw materials. However, the strong electrostatic interaction between bivalent Mg-ions and host lattices often cause sluggish solid state diffusion of Mg-ion within the local crystal structure and consequently prevent reversible insertion/extraction of Mg-ion. Thus much more effort has been paid to develop suitable electrode materials with Mg-ion storage capability. This paper reports the synthesis of Sn nanoparticles/reduced-graphene-oxide nanosheet hybrid nanocomposite (Sn/rGO), by simple hydrothermal method and subsequent thermal treatment. Transmission electron microscopy (TEM) clearly shows that in the as-synthesized Sn/rGO powder Sn nanoparticles are well crystallized, and X-ray diffraction (XRD) pattern was consistent well with tetragonal Sn. Thermogravimetric analysis (TG) suggested that the mass percentage of Sn is ca. 82.3 wt% in the Sn/rGO nanocomposite, very close to the design ratio of ca. 83.4 wt%. As Mg-ion battery anode, the Sn/rGO electrode material exhibit a high initial discharge specific capacity (545.4 mAh.g(-1) at 15 mA.g(-1)), good reversible ability and rate performance. The impressive electrochemical property could be attributed to the unique structure of Sn/rGO, in which the three-dimensional (3D) conducting network of rGO can effectively prevent the aggregation of Sn nanoparticles and alleviate the serious volume variation of Sn during repeated discharging/charging process, as well as facilitate the fast access of electrons and Mg-ion to improve kinetics for Mg-ion insertion/extraction. Ex situ XRD and SEM characterization were performed to investigate the electrochemical evolution of Sn/ rGO electrode at different discharging/charging states. It is found that upon magnesiation crystalline Mg2Sn appears and subsequently disappears during de-magnesiation process, which indicates the good electrochemical activity of Sn nanoparticles in Sn/ rGO hybrid nanocomposite for magnesium storage. Our result will open new avenue to develop high-efficient magnesium storage material for rechargeable Mg batteries.