Morphology Engineering of VS4 Microspheres as High-Performance Cathodes for Hybrid Mg2+/Li+ Batteries.

V-based sulfides are considered as potential cathode materials for Mg2+/Li+ hybrid ion batteries (MLIBs) due to their high theoretical specific capacities, unique crystal structure, and flexible valence adjustability. However, the formation of irreversible polysulfides, poor cycling performance, and severe structural collapse at high current densities impede their further development. Herein, VS4 microspheres with various controllable nanoarchitectures were successfully constructed via a facile solvothermal method by adjusting the amount of hydrochloric acid and were used as cathode materials for MLIBs. The VS4 microsphere self-assembled by bundles of paralleled-nanorods and some intersected-nanorods (VS4@NC-5) exhibits an outstanding initial discharge capacity of 805.4 mAh g-1 at 50 mA g-1 that is maintained at 259.1 mAh g-1 after 70 cycles. Moreover, the VS4@NC-5 cathode can deliver a superior rate capability (146.1 mAh g-1 at 2000 mA g-1) and ultralong cycling life (134.5 mAh g-1 at 2000 mA g-1 after 2000 cycles). The extraordinary electrochemical performance of VS4@NC-5 could be attributed to its special multi-hierarchical microsphere structure and the formation of N-doped carbon layers and V-C bonds, resulting in unobstructed ion diffusion channels, multidimensional electron transfer pathways, and enhancements of electrical conductivity and structure stability. Furthermore, the electrochemical reaction mechanism and phase conversion behavior of the VS4@NC-5 cathode at various states are investigated by a series of ex situ characterization methods. The VS4 well-designed through morphological engineering in this work can pave a way to explore more sulfides with high-rate performance and long cycling stability for energy storage devices.