SILICON/GRAPHITE NANO-STRUCTURED COMPOSITES FOR A HIGH EFFICIENCY LITHIUM-ION BATTERIES ANODE

Si/C composites have been employed in an attempt to overcome the problems of Si-based negative Li-ion electrodes. The composites were produced by coating, followed by a two-step solid state reaction. Electrodes were prepared therefrom by spreading on a Cu foil. The materials were characterized by SEM and XRD. The Si phase in the composite shows an enhanced crystalline Structure compared to the pristine Si powder. Electrochemical cycling tests displayed two discharge plateaus at 0.250 and 0.1 V, where lithiated amorphous Si is formed and the entire crystalline phase is completely depleted. During the Li extraction the composite shows a distinct plateau at 0.45 V, where delithiated amorphous Si is formed. The behaviour of the composite was investigated in a IM LiPF6/EMC (ethylene carbonate:ethyl methyl carbonate, 1:2) electrolyte with and without vinylene carbonate additives. The VC-based electrolyte exhibited a better efficiency, approaching 99.2% after the first few cycles and remaining constant in the next 30 cycles.