Unlocking efficient energy storage via regulating ion and electron-active subunits: an (SbS)1.15TiS2 superlattice for large and fast Na+ storage

Alloying-type metal sulfides with high sodiation activity and theoretical capacity are promising anode materials for high energy density sodium ion batteries. However, the large volume change and the migratory and aggregation behavior of metal atoms will cause severe capacity decay during the charge/discharge process. Herein, a robust and conductive TiS₂ framework is integrated with a high-capacity SbS layer to construct a single phase (SbS)_1.15TiS₂ superlattice for both high-capacity and fast Na⁺ storage. The metallic TiS₂ sublayer with high electron activity acts as a robust and conductive skeleton to buffer the volume expansion caused by conversion and alloying reaction between Na⁺ and SbS sublayer. Hence, high capacity and high rate capability can be synergistically realized in a single phase (SbS)_1.15TiS₂ superlattice. The novel (SbS)_1.15TiS₂ anode has a high charge capacity of 618 mAh g⁻¹ at 0.2 C and superior rate performance and cycling stability (205 mAh g⁻¹ at 35 C after 2,000 cycles). Furthermore, in situ and ex situ characterizations are applied to get an insight into the multi-step reaction mechanism. The integrity of robust Na-Ti-S skeleton during (dis)charge process can be confirmed. This superlattice construction idea to integrate the Na⁺-active unit and electron-active unit would provide a new avenue for exploring high-performance anode materials for advanced sodium-ion batteries.