Structural phase transformation from SnS2/reduced graphene oxide to SnS/sulfur-doped graphene and its lithium storage properties

Abstract

In this work, we demonstrate an interesting structural phase transition from SnS₂/reduced graphene oxide to SnS/sulfur-doped graphene at a moderate calcination temperature of 500 °C under an inert atmosphere. It is discovered that SnS₂ chemically bound to rGO with a weakened C–S bond is easier to break and decompose into SnS, whereas it is difficult for pure-phase crystalline SnS₂ to experience phase transformation at this temperature. Moreover, the thin-layered structure of SnS₂ and rGO is an important factor for the effective doping of the dissociated S_x into graphene. Density functional theory calculations also reveal the feasibility of the structural phase transition process. Morphology characterization shows that partial SnS maintains the original nanosheet structure (∼100 nm) and the others are decomposed into tiny nanoparticles (10–20 nm). A high S-doping amount reduces the irreversible lithium storage sites on graphene, and the first coulombic efficiency is as high as 81.7%. In addition, thin-layered and small-sized SnS can alleviate the structural damage caused by volume expansion and shrinkage; therefore, a high specific capacity of 893.9 mA h g⁻¹ is retained after 100 cycles.