Ammonium-Modified Synthesis of Vanadium Sulfide Nanosheet Assemblies toward High Sodium Storage

The weak van der Waals interactions of the one-dimensional (1D) chainlike VS4 crystal structure can enable fast charge-transfer kinetics in metal ion batteries, but its potential has been rarely exploited in depth. Herein, a thermodynamics-driven morphology manipulation strategy is reported to tailor VS4 nanosheets into 3D hierarchical self-assembled architectures including nanospheres, hollow nanospheres, and nanoflowers. The ultrathin VS4 nanosheets are generated via 2D anisotropic growth by the strong driving force of coordination interaction from ammonium ions under microwave irradiation and then evolve into 3D sheet-assembled configurations by adjusting the thermodynamic factors of temperature and reaction time. The as-synthesized VS4 nanomaterials present good electrochemical performances as the anode materials for sodium-ion batteries. In particular, the hollow VS4 nanospheres show a specific capacity of 1226.7 mAh g-1 at 200 mA g-1 current density after 100 cycles. The hierarchical nanostructures with large specific surface area and structural stability can overcome the difficulty of sodium ions embedding into the bulk material interior and provide more reactive materials at the same material mass loading compared with other morphologies. Both experiment and DFT calculations suggest that VS4 nanosheets reduce reaction kinetic impediment of sodium ion in battery operating. This work demonstrates a way of the morphological design of 2D VS4 nanosheets and application in sodium ion storage.