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.