Tin Sulfide(SnS) 3-D Nanoflowers with Superb Kinetic Property for the Anodic Use in Next-Generation Sodium Rechargeable Battery

The ever-increasing demands of high power/energy density battery for electric vehicles (EVs) and hybrid electric vehicles (HEVs) as well as large-scale energy storage systems (ESSs) bring about the development of next-generation rechargeable battery systems with price competitiveness. Lithium rechargeable battery has been considered as a promising candidate for energy storage because of its high energy density. Unfortunately, the utilization of lithium rechargeable battery for large scale applications is restricted due to limited lithium resources leading to high cost. On the other hand, sodium metals and sodium compounds indeed have merits in terms of cost and suitable redox potential of Na ions (Na/Na⁺= 2.71 V vs. SHE at 298 K, 1 M, 1 atm), which can facilitate to commercialize sodium rechargeable battery for large scale application. Even if sodium rechargeable battery has recently attracted considerable interest, it still has low efficiency and poor cycle life at present. Such drawbacks are mainly attributed to the large ionic radius of Na ion (35% larger than Li ion), which may prompt mechanical stress and poor Na ion diffusivity in active materials of both cathode and anode sides. Therefore, there have been many attempts to design well-tailored materials for sodium rechargeable battery. Among them, metal sulfides have been extensively studied due to their fundamental properties for important technological applications. In particular, SnS has attracted much attention recently due to high theoretical capacity of 1,022 mAh/g, which is attributed to conversion and alloying-dealloying reaction with Na ion.

Here, we devised SnS three-dimensional (3-D) nanoflowers containing hierarchically organized two-dimensional (2-D) nanosheet subunits. Based on the electrochemical observations, SnS 3-D nanoflowers revealed that the unique morphology with large surface area and electrochemical interfacial region facilitates highly efficient Na ion insertion and extraction compared to those of bulk counterparts. Futhermore, the ex-situ characterizations let us know that the space between the each individual 2-D nanosheet subunit can effectively accommodates volume changes during charge/discharge process. Thus, the SnS 3-D nanoflowers can be considered as one of the most promising anode materials with superb kinetic property and stable cycle performance for sodium rechargeable battery.