Rational design of robust Fe7S8-FeP@NC anode with coherent heterogeneous structure for sodium-ion batteries

The use of state-of-the-art Fe-based compounds as the anode material for sodium ion batteries can push the discharge capacity and cyclic stability to a superior level than is currently available. However, particle agglomeration and rupture related to volume changes that is being created during sodium (de)intercalation cause intense physicochemical instability and electrochemical degradation, especially at large current density. Here, we engineered a Fe₇S₈-FeP heterogeneous structure, with Fe₇S₈-FeP particles anchored and uniformly dispersed on a nitrogen-doped carbon substrate (Fe₇S₈-FeP@NC). This configuration exhibits an impressive average specific capacity of 179.9 mAh g⁻¹ at a high current density of 10 A g⁻¹, while retaining a substantial reversible discharge capacity of 217 mAh g⁻¹ after 3000 cycles at 3 A g⁻¹, thereby demonstrating both enhanced rate capability and cycle stability. Moreover, it still achieved 66.3 % capacity retention at 1 A g⁻¹ after 800 cycles in full cell. Additionally, it is clarified that the heterogeneous structure enables to furnish abundant active sites and shorten the transmission path of Na⁺, thus effectively improving reaction dynamics and stability performance. This study clarifies the unique stability of heterogeneous structure, providing a feasible synthesis method for preparing metal phosphorus vulcanized compounds with heterogeneous structure.