Confining WS hierarchical structures into carbon core-shells for enhanced sodium storage.

The growing demand for clean energy has heightened interest in sodium-ion batteries (SIBs) as promising candidates for large-scale energy storage. However, the sluggish reaction kinetics and significant volumetric changes in anode materials present challenges to the electrochemical performance of SIBs. This work introduces a hierarchical structure where WS is confined between an inner hard carbon core and an outer nitrogen-doped carbon shell, forming HC@WS@NCs core-shell structures as anodes for SIBs. The inner hard carbon core and outer nitrogen-doped carbon shell anchor WS, enhancing its structural integrity. The highly conductive carbon materials accelerate electron transport during charge/discharge, while the rationally constructed interfaces between carbon and WS regulate the interfacial energy barrier and electric field distribution, improving ion transport. This synergistic interaction results in superior electrochemical performance: the HC@WS@NCs anode delivers a high capacity of 370 mAh g at 0.2 A/g after 200 cycles and retains261 mAh g at 2 A/g after 2000 cycles. In a full battery with a NaV(PO) cathode, the NaV(PO)//HC@WS@NC full-cell achieves an impressive initial capacity of 220 mAh g at 1 A/g. This work provides a strategic approach for the systematic development of WS-based anode materials for SIBs.