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

V-based sulfides are considered aspotential cathode materialsfor Mg2+/Li+ hybrid ion batteries (MLIBs) dueto their high theoretical specific capacities, unique crystal structure,and flexible valence adjustability. However, the formation of irreversiblepolysulfides, poor cycling performance, and severe structural collapseat high current densities impede their further development. Herein,VS4 microspheres with various controllable nanoarchitectureswere successfully constructed via a facile solvothermal method byadjusting the amount of hydrochloric acid and were used as cathodematerials for MLIBs. The VS4 microsphere self-assembledby bundles of paralleled-nanorods and some intersected-nanorods (VS4@NC-5) exhibits an outstanding initial discharge capacityof 805.4 mAh g(-1) at 50 mA g(-1) thatis maintained at 259.1 mAh g(-1) after 70 cycles.Moreover, the VS4@NC-5 cathode can deliver a superior ratecapability (146.1 mAh g(-1) at 2000 mA g(-1)) and ultralong cycling life (134.5 mAh g(-1) at2000 mA g(-1) after 2000 cycles). The extraordinaryelectrochemical performance of VS4@NC-5 could be attributedto its special multi-hierarchical microsphere structure and the formationof N-doped carbon layers and V-C bonds, resulting in unobstructedion diffusion channels, multidimensional electron transfer pathways,and enhancements of electrical conductivity and structure stability.Furthermore, the electrochemical reaction mechanism and phase conversionbehavior of the VS4@NC-5 cathode at various states areinvestigated by a series of ex situ characterization methods. TheVS(4) well-designed through morphological engineering inthis work can pave a way to explore more sulfides with high-rate performanceand long cycling stability for energy storage devices.

Automated summary

VS4 microspheres with controllable nanoarchitectures were successfully constructed and used as cathode materials for MLIBs. The VS4@NC-5 microspheres exhibited outstanding initial discharge capacity, superior rate capability, and ultralong cycling life due to their special multi-hierarchical microsphere structure, N-doped carbon layers, and V-C bonds.