Synergistic interface and structural engineering for high initial coulombic efficiency and stable sodium storage in...

Transition metal sulfides (TMS) have gained significant attention as potential anode materials for sodium ion batteries (SIBs) due to their high theoretical capacity and abundance in nature. Nevertheless, their practical use has been impeded by challenges such as large volume changes, unstable solid electrolyte interphase (SEI), and low initial coulombic efficiency (ICE). To address these issues and achieve both long-term cycling stability and high ICE simultaneously, we present a novel approach involving surface engineering, termed as the "dual-polar confinement" strategy, combined with interface engineering to enhance the electrochemical performance of TMS. In this approach, CoS crystals are meticulously coated with polar TiO₂ and embedded within a polar S-doped carbon matrix, forming a composite electrode denoted as CoS/TiO₂-SC. Significantly, an ether-based electrolyte with chemical stability and optimized solvation properties synergistically interacts with the Co-S-C bonds to create a stable, ultra-thin SEI. This concerted effect results in a notably high ICE, reaching approximately 96%. Advanced characterization and theoretical simulations confirm that the uniform surface modification effectively facilitates sodium ion transport kinetics, restrains electrode pulverization, and concurrently enhances interaction with the ether-based electrolyte to establish a robust SEI. Consequently, the CoS/TiO₂-SC electrode exhibits high reversible capacity, superior rate capability, and outstanding cycling stability.