Upgraded lithium storage performance of defect-rich Si@C anode assisted by Fe2O3-induced pseudocapacitance

Abstract

Following a flowsheet comprised of a hydrothermal reaction and a dehydration/carbonization, Si-xFe/O@C anodes featured with Fe-doping and carbon encapsulation were assembled. Comparing with pure Si, Si disseminated with in situ generated nano-scaled ferric oxide (Fe2O3) particulates displays remarkably improved cyclic performance. Fe2O3 may induce amorphization and optimize electrical conductivity, by enhancing the formation of Fe and Li2O amidst charging-discharging cycles. The as-derived Fe phase benefits the transport and storage of lithium-ion and electrons. Meanwhile, numerous tiny interfaces can be constructed between Fe granules and adjacent LixSi or Li2O, and generate pseudocapacitance. After the carbonization of resorcinol-formaldehyde resin encapsulated on Si granules, core-shell structured Si-xFe/O@C particulates can be assembled. Owing to the synergism of defect-rich structure, carbon layer well-wrapped thereon and interfacial pseudocapacitance, these nanocomposite anode materials exhibit long cyclic and upgraded rate performance. After 200 cycles, Si-0.42Fe/O@C anode retains a capacity of 929 mAh·g−1 at 1 A·g−1 and 735 mAh·g−1 at 2 A·g−1. In the rate performance test operated at 5 A·g−1, a high current density, 844 mAh·g−1 could be released. Si-0.42Fe/O@C can be charged with a specific capacity exceeding 250 mAh·g−1 over the potential range of 0.75-3 V at various current densities, demonstrating the contribution of nano-Fe pseudocapacitance effect to the energy storage of Si anodes.