Double-coated SnS with hierarchical carbon network as high-performance anode materials for sodium-ion batteries

Two-dimensional (2D) layered metal sulfides have shown great potentials for sodium-ion anode materials owing to fast interlayer diffusion. As one of 2D layered metal sulfides, SnS has been widely studied because of its high theoretical specific capacity (1022 mAh/g vs 372 mAh/g for hard carbon) and large interlayer spacing (4.33 Å vs about 3.4 Å for hard carbon). However, SnS still face several problems, such as low electronic conductivity, large volume change, dissolution of intermediate products, and poor structural stability. To solve these problems, herein, tin sulfide (SnS)/carbon hybrid materials were prepared through simple solvothermal and subsequent sintering processes. By a one-pot synthesis, SnS nanospheres were in-situ coated with pyrolytic carbon and wrapped by conductive reduced graphene oxide sheets (SnS@C@rGO). This hierarchical carbon network enhances electronic conductivity of the SnS@C@rGO hybrid, leading to enhanced rate performance. Moreover, the in situ pyrolytic carbon coating can alleviate the dissolution of intermediates and buffer the volume change of the SnS material, while the graphene wrapping can further improve the structural stability, leading to enhanced cycling performance. When used as anode material, the double-coated SnS@C@rGO anode delivered the highest retention capacity of 383.5 mAh/g after 100 cycles at a current density of 1 A/g, when compared with SnS@C (114.4 mAh/g) and SnS@rGO (230.7 mAh/g). Even at a high current density of 5 A/g, the SnS@C@rGO anode still delivered a high retention capacity of 312.2 mAh/g after 500 cycles, when compared with SnS@C (119.3 mAh/g) and SnS@rGO (140.1 mAh/g). This work demonstrates an effective strategy of double carbon coating for enhancing structural stability and battery performance of SnS anode materials, which can also be used to modify other anode materials for sodium- and lithium-ion batteries.