Nanosized tin and tin oxides loaded expanded mesocarbon microbeads as negative electrode material for lithium-ion batteries

Tin-based composites using expanded mesocarbon microbeads (EMCMB) as matrix were prepared by impregnating tin chloride and the following reduction under hydrogen atmosphere at different temperatures. The morphologies and structural characteristics of the composites were investigated by FE-SEM, EDS and XRD measurements. It was found that tin exists inside EMCMB in the form of oxidation states (Sn(II) and Sn(IV)) after reduction at lower temperature (below 350 °C), and metallic tin exists both outside EMCMB and between carbon layers after reduction at higher temperature (450 °C). The electrochemical properties of the composites as negative electrode material for lithium-ion batteries were systematically investigated by cyclic voltammetry, galvanostatic cycling and electrochemical impedance spectroscopy tests. The results showed that loading amount of tin or tin oxides and reduction temperature had large influences on the reversible capacity and cycle performance of these composites. Among them, the composite reduced at 230 °C with appropriate loading amount of tin oxides not only exhibited the high first reversible gravimetric capacity of 401 mAh g−1 and an excellent cyclability with only 0.2% capacity loss/cycle at lower current density, but also showed a stable cycle performance at higher current density due to its lower resistance.