Gas-expansion strategy for synchronizing high-rate and ultra-stable sodium storage of Fe₇S₈@NSC anode

Due to its high reversible capacity, Fe₇S₈ has emerged as a promising anode material for sodium-ion batteries (SIBs). However, its application is limited by slow reaction kinetics and significant volume expansion during the charging and discharging process, resulting in poor rate capacity and reduced cycling stability. To address these issues, a novel high-temperature gas-expansion method is proposed to uniformly incorporate Fe₇S₈ nanoparticles into N and S co-doped porous carbon (Fe₇S₈@NSC). It effectively reduces the volume expansion of Fe₇S₈ and improves its electron/ion conductivity. As a result, when used as an anode material in SIBs, Fe₇S₈@NSC demonstrates excellent rate performance, delivering a capacity of 500.0 mAh/g at a current density of 5 A/g. Additionally, it exhibits remarkable stability, maintaining 99.83 % of its capacity after 600 cycles at the same high current density.