Tin-iron based high capacity anodes for lithium-ion batteries.

摘要

Since the demand for more powerful and smaller batteries is constantly increasing, finding new cathode and anode materials for Li-ion batteries has thus become a necessity. Recently, some progress has been made on cathode materials, for example the commercialization of LiFePO4. However, no real improvement has been reported for anode materials. Graphite is still dominant in today's battery; however it suffers from a low volumetric energy density. To overcome this, we have investigated Sn-Fe-C composites, which have the potential of doubling the volumetric capacity of graphite. In this study, we used two approaches to synthesize tin-iron materials: mechanochemical and hydrothermal methods.;Nanosized Sn-Fe-C anode materials were mechanochemically synthesized by reducing SnO with Ti in the presence of carbon. The mechanochemically synthesized Sn-Fe-C composite, unlike pure tin itself, which loses capacity very rapidly on cycling, maintains its capacity for more than 100 charge-discharge cycles. The electrochemical performance of the composite was further improved by optimizing the synthesis conditions, such as total grinding time, grinding media, the ratios of the reactants and the types of carbon. The optimized composite shows excellent extended cycling at C/10, delivering a first lithiation capacity as high as 740 mAh/g and 60 % of the capacity is retained after 170 cycles. In addition to the better cycling performance, the material also doubles the volumetric capacity of a graphite-based anode at 1C rate over 100 cycles.;Sn2Fe-based anode materials were also synthesized by the alternative solvothermal route, and the electrochemical performance was evaluated. To have a comprehensive understanding of the electrochemical mechanism of this Sn2Fe material, the structural evolution during cycling was investigated by synchrotron X-ray diffraction (XRD), X-ray Absorption Spectroscopy (XAS), and magnetic studies. Studies of the first cycle show that Li-Sn alloys were formed upon lithiation accompanied by the extrusion of metallic iron phase, while almost all the Sn2Fe was recovered at the end of delithiation with small portion of Fe remaining inactive. The second cycle shows a similar behavior, but with a faster structural evolution.