Tin-based nanocomposite alloy anodes for lithium-ion batteries
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Lithium-alloying anode materials have attracted much attention as an alternative to carbon due to their high theoretical gravimetric capacities (e.g. Li4.4Si: 4200 mAh g-1, Li4.4Sn: 990 mAh g-1, and Li3Sb: 660 mAh g-1). An additional benefit of lithium alloying metals is that some of the react at a higher potentials vs. Li/Li+ than carbon, which can mitigate safety issues caused by solid-electrolyte interface layer formation and lithium plating. One of the most promising lithium -alloying anode materials that are being pursued are Sn-based materials due to their high capacity and tap density. This thesis investigates the synthesis and characterization of Sn-based lithium-ion battery anodes. SnSb-TiC-C and FeSn2-TiC nanocomposite alloy anodes for lithium-ion batteries have been synthesized by a mechanochemical process involving high-energy mechanical milling of Ti/Sn, Ti/M (M = Fe or Sb), and C. Characterization of the nanocomposites formed with x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) reveals that these alloys are composed of crystalline nanoparticles of FeSn2 and SnSb dispersed in a matrix of TiC and carbon. The SnSb-TiC-C alloy shows an initial gravimetric capacity of 653 mAh g-1 (1384 mAh cm-3), an initial coulombic efficiency of 85%, and a tap density of 1.8 g cm-3. The FeSn2-TiC alloy shows an initial gravimetric capacity of 510 mAh g-1 (1073 mAh cm-3), an initial coulombic efficiency of 71%, and a tap density of 2.1 g cm-3. The TiC-C buffer matrix in the nanocomposite alloy anodes accommodates the large volume change occurring during the charge-discharge process and leads to good cyclability compared to pure FeSn2 and SnSb anodes.