Novel compositional-gradient hierarchical ZnS/GeS2 heterojunction nanorods for high-rate and durable sodium storage

Abstract

Transition metal sulfides (TMSs) are attractive anode materials for sodium-ion batteries because of their high theoretical capacities and reversible conversion chemistry. However, the sluggish charge transfer and large volume changes of TMSs during repeated Na⁺ insertion and extraction result in inferior rate capability and cycle life, hindering their practical applications. Herein, we report a controllable interdiffusion and vulcanization method for designing hierarchical composition-gradient ZnS/GeS₂/C heterojunction nanorods from Zn₂GeO₄ precursors. During high-temperature sulfidation, the mutual diffusion of differential elements forms a ZnS-rich shell and a GeS₂-rich core, thereby generating abundant ZnS/GeS₂ heterointerfaces within a conductive carbon matrix. The in situ formed heterointerfaces between ZnS and GeS₂ facilitate interfacial electronic and ionic transport, while the composition gradient interacts with the carbon network to redistribute mechanical stress and mitigate fragmentation of active material upon long-term cycling. As a result, the prepared ZGS/C anode delivers a reversible capacity of 663.6 mAh g⁻¹ at 1.0 A g⁻¹ and retains 389.6 mAh g⁻¹ after 6000 cycles at 10 A g⁻¹. Additionally, the full cell with a Na₃V₂(PO₄)₃ cathode exhibits an initial reversible capacity of 347.8 mAh g⁻¹ at 0.5 A g⁻¹, with a capacity retention ratio of 77.6% after 200 cycles. The work on the interdiffusion and vulcanization approach provides scalable strategies for heterointerface engineering of multicomponent sulfide anodes.