In situ analysis of SnO2/Fe2O3/RGO to unravel the structural collapse mechanism and enhanced electrical conductivity for lithium-ion batteries

Herein, we describe a microwave-assisted hydrothermal process to synthesize α-Fe2O3 nanotubes/SnO2 nanorods/reduced graphene oxide (FNT/S/RGO) for application as a high-performance anode in lithium-ion batteries (LIBs). The composite products exhibit anisotropic growth because of heteronucleation and the preferred orientation of SnO2. SnO2 nanorods on the FNT surfaces are converted into Sn metal during the alloying/dealloying reaction, which offers improved electrical conductivity. The FNT/S/RGO show substantially enhanced electrochemical properties because of the reduced volume expansion effect, which improves the electrical and Li-ion conductivity and provides a large surface area. As a consequence, the FNT/S/RGO anode delivers a high reversible capacity of 883 mA h g−1 even at a current density of 200 mA g−1, with a capacity retention of 90% between the 1st and 220th cycles, excellent high-rate capacity (382 mA h g−1 at 4320 mA g−1), and long-term cycle durability (maintaining 629 mA h g−1 at 1000 mA g−1 for 1000 cycles). The presented FNT/S/RGO electrodes are the most efficient SnO2- and Fe2O3-based anode electrodes reported thus far for LIBs. The origin of the synergistic effect and the reaction mechanism of the FNT/S/RGO was thoroughly investigated using various in situ transmission electron microscopy, electrochemical impedance spectroscopy, and X-ray diffraction analysis methods.