Surface modification of tin oxide through reduced graphene oxide as a highly efficient cathode material for magnesium-ion batteries.

Among post-lithium ion technologies, magnesium-ion batteries (MIBs) are receiving great concern in recent years. However, MIBs are mainly restrained by the lack of cathode materials, which may accommodate the fast diffusion kinetics of Mg ions. To overcome this problem, herein we attempt to synthesize a reduced graphene oxide (rGO) encapsulated tin oxide (SnO) nanoparticles composites through an electrostatic-interaction-induced-self-assembly approach at low temperature. The surface modification of SnO via carbonaceous coating enhanced the electrical conductivity of final composites. The SnO-rGO composites with different weight ratios of rGO and SnO are employed as cathode material in magnesium-ion batteries. Experimental results show that MIB exhibits a maximum specific capacity of 222 mAhg at the current density of 20 mAg with a good cycle life (capacity retention of 90%). Unlike Li-ion batteries, no SnO nanoparticles expansion is observed during electrochemical cycling in all-phenyl-complex (APC) magnesium electrolytes, which ultimately improves the capacity retention. Furthermore, ex-situ x-ray diffraction and scanning electron microscopy (SEM) studies are used to understand the magnesiation/de-magnesiation mechanisms. At the end, SnO-rGO composites are tested for Mg/Li hybrid ion batteries and results reveal a specific capacity of 350 mAhg at the current density of 20 mAg. However, hybrid ion battery exhibited sharp decay in capacity owing to volume expansion of SnO based cathodes. This work will provide a new insight for synthesis of electrode materials for energy storage devices.