Soft-Rigid Heterostructures with Functional Cation Vacancies for Fast-Charging and High-Capacity Sodium Storage

Optimizing charge transfer and alleviating volume expansion in electrode materials are critical to maximize electrochemical performance for energy-storage systems. Herein, an atomically thin soft-rigid Co₉ S₈ @MoS₂ core-shell heterostructure with dual cation vacancies at the atomic interface is constructed as a promising anode for high-performance sodium-ion batteries. The dual cation vacancies involving V_Co and V_Mo in the heterostructure and the soft MoS₂ shell afford ionic pathways for rapid charge transfer, as well as the rigid Co₉ S₈ core acting as the dominant active component and resisting structural deformation during charge-discharge. Electrochemical testing and theoretical calculations demonstrate both excellent Na⁺ -transfer kinetics and pseudocapacitive behavior. Consequently, the soft-rigid heterostructure delivers extraordinary sodium-storage performance (389.7 mA h g^-1 after 500 cycles at 5.0 A g^-1 ), superior to those of the single-phase counterparts: the assembled Na₃ V₂ (PO₄ )₃ ||d-Co₉ S₈ @MoS₂ /S-Gr full cell achieves an energy density of 235.5 Wh kg^-1 at 0.5 C. This finding opens up a unique strategy of soft-rigid heterostructure and broadens the horizons of material design in energy storage and conversion.