Ultrahigh rate sodium-ion storage of SnS/SnS2 heterostructures anchored on S-doped reduced graphene oxide by ion-assisted growth

Developing high-performance anode materials is very crucial for room-temperature sodium-ion batteries (SIBs). Sn-based compounds are promising SIB anode materials for their high theoretical capacities and low costs. However, the intrinsic low conductivity, poor infiltration and irreversible reactions of Sn-based compounds lead to poor rate and cycling performance. In order to address above issues, SnS/SnS2 heterostructures on sulfur-doped reduced graphene oxide (SG) are assembled via a facile alkali ion-assisted growth. As-synthesized SnS/SnS2 heterostructures on SG with assistance of K+, denoted as SnS/SnS2@SG-K, exhibits typical layer-stacked structure and high reversible capacities over 800 mAh g−1 at 50 mA g−1 and 241 mAh g−1 even at a record high current density of 48 A g−1, which are superior to most of the Sn-based SIB anode materials. The excellent rate and cycling performance of SnS/SnS2@SG-K could be ascribed to the layer-stacked structures of SG and heterojunctions between SnS and SnS2 which can accelerate semi-infinite diffusions of Na+ ions and electrons, alleviate polysulfide shuttling problems and reduce volume fluctuation effect. Meanwhile, the pseudocapacitance of oxygen and sulfur-containing groups in SG also contribute to the unprecedented sodium storage performance of as-synthesized SnS/SnS2@SG-K.