中文摘要：

镁二次电池具有安全性高、价格低廉等优点，是一种具有潜在应用前景的高能量密度电池体系．目前，镁二次电池的研究重点之一是寻找合适的电极材料．最近，我们通过水热和热处理相结合的方法成功制备了具有三维导电网络结构的锡纳米颗粒／石墨烯纳米片复合电极材料．研究发现，在石墨烯的三维导电网络片层上，均匀分布了粒径小于100nm的锡纳米颗粒．将锡纳米颗粒／石墨烯纳米片复合材料作为镁二次电池电极材料，当电流密度为15mA·g-1和300mAog-1时，首次放电容量分别达到了545．4mAh·g-1和238．8mAh·g-1，经过150圈后，容量保持率达到了93％，库伦效率为99％．表现出了较高的电化学活性．研究还发现，镁离子嵌入复合材料中形成镁锡合金，当镁离子脱出后，再次形成锡纳米颗粒／石墨烯纳米片复合电极材料，镁离子的脱出和嵌入具有很高的可逆性．这对未来研究设计高性能镁离子电极材料具有十分重要的意义．

英文摘要：

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 mAo·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 ofrGO 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 nanopart