Structural engineering of yolk-shell FeSe2 nanorods: toward high-performance anodes for sodium-ion batteries

Sodium-ion batteries (SIBs) are promising for large-scale energy storage due to their safety, low-temperature performance and cost benefits. However, the large size of Na⁺ ions causes mechanical stress in electrodes during cycling, leading to capacity loss. This study demonstrates a yolk-shell structured FeSe₂@nitrogen-doped carbon composite (YS-FeSe₂@NC) through vapor-phase selenization approach. The YS-FeSe₂@NC anode features an N-doped carbon coating that enhances electrical conductivity and ion transport, along with a precisely designed cavity structure that minimizes volume changes during charge/discharge, leading to excellent electrochemical performance. The anode retains a reversible capacity of 430.4 mAh g⁻¹ after 2000 cycles at 5 A g⁻¹. Ex-situ XPS and SEM analyses show that the improved sodium storage performance of YS-FeSe₂@NC is mainly due to enhanced electrode kinetics and stable SEI formation, both resulting from the combined effects of the yolk-shell structure and N-doped carbon layer.