Core-shell Fe3O4@Fe ultrafine nanoparticles as advanced anodes for Li-ion batteries

Core-shell Fe 3 O 4 @Fe ultrafine nanoparticles (nano-Fe 3 O 4 @Fe, Fe 3 O 4 content 84 wt%) with a core (Fe) diameter of 5.1 ± 1.4 nm and a shell (Fe 3 O 4 ) diameter of 10.9 ± 1.6 nm is prepared by a liquid-phase pyrolysis and partial oxidation method. It is found that the core-shell Fe 3 O 4 @Fe ultrafine nanostructure can efficiently improve the electrochemical performance of Fe 3 O 4 as anode material for Li-ion batteries in terms of rate capability and cycle life. For instance, specific capacities of 884 and 705 mAh/g can be obtained for the nano-Fe 3 O 4 @Fe electrode after 100 cycles at 200 mA/g and 500 cycles at 1000 mA/g, respectively. It is believed that these improvements can be attributed to the significant shortened transfer distance of electrons and Li-ions with relatively low specific surface area, ultrahigh electronic conductivity inside the nanoparticles and good ductility to accommodate the asymmetric volume change.