The Multicomponent Synergistic Effect of Sandwich Structure Hierarchical Nanofibers for Enhanced Sodium Storage

Constructing hierarchical micro/nanostructures as anodes for sodium ion batteries is an important approach for exploiting efficient energy storage devices. Herein, sandwich structure hierarchical nanofibers composed of hollow carbon fibers as the substrate, and MoS2 as the interlayer with Co and/or ZnS nanoparticles anchoring in carbon skeletons as the outer shell (carbon nanofiber/MoS2 /Co-ZnS⊂NC) are prepared via a multistep reaction strategy. Profiting from the unique hierarchical structure, abundant migration channels of Na+ , and multicomponent synergistic effects, the rapid diffusion kinetics are ensured and the utilization of active materials is maximized. The coaxial structure can evenly disperse volumetric strain, making structural stability guaranteed. Hierarchical nanofibers deliver a high reversible capacity of 352.3 mAh g-1 at 5.0 A g-1 over 3000 cycles. A discharge capacity of 182.5 mAh g-1 is retained even after 10 000 cycles at 10.0 A g-1 as well as a high rate capacity of 202.0 mAh g-1 up to 30 A g-1 . The optimal atomic ratio of Co element is further verified by the kinetic analysis. The full-cells assembled with Na3 V2 (PO4 )3 cathode provide a high capacity of 179.2 mAh g-1 at 1.0 A g-1 for 500 cycles. Combining in situ and ex situ characterizations and theoretical calculations, possible sodium storage mechanisms and the origin of superior electrochemical properties are revealed.