Interlayer gap widened TiS2 for highly efficient sodium-ion storage

As an alternative for lithium-ion batteries (LIBs), sodium-ion batteries (SIBs) have lately received tremendous interest due to their abundant reserves as well as low cost. Nevertheless, the lack of suitable anode materials severely hinders the application of sodium-ion batteries. TiS2 is elected as a representative material owing to its unique layered structure. But it always suffers from capacity fade due to poor electrochemical kinetics and structural stability. In this work, we fabricate a pre-potassiated TiS2 as a host material for sodium storage by an electrochemical pre-potassiation strategy. The intercalation/extraction mechanism, structural changes and reaction kinetics are completely investigated to reveal the outstanding electrochemical property of pre-potassiated TiS2 electrode. It turns out that the large interlayer space of pre-potassiated TiS2 is conducive to the diffusion of sodium ions, inducing the reduction of entropic barrier for the electrochemical reactions. In addition, the pre-potassiated host structure is still firmly maintained upon repeated cycles. Therefore, the pre-potassiated TiS2 presents superior rate capability (165.9 mA h g − 1 at 1 C and 132.1 mA h g − 1 at 20 C) and long-term cycling stability (85.3% capacity retention at 5 C after 500 cycles) for SIBs. This research provides an avenue to construct long-life sodium energy storage systems based on pre-potassiated TiS2.