Structural Stability Boosted in 3D Carbon‐Free Iron Selenide through Engineering Heterointerfaces with SeP Bonds for Appealing Na+‐Storage

Abstract Iron selenides have emerged as appealing anodes for Na + ‐storage due to their natural abundance, good redox reversibility, and high theoretical capacity. Nevertheless, exploring a carbon‐free iron selenide anode with long‐term stability and high‐rate capability remains an intractable challenge. Herein, a 3D carbon‐free iron selenide electrode is designed by heterointerface with SeP bond engineering strategy to realize outstanding Na + ‐storage performance. Theoretical calculations on the stress deformation confirm the construction of Fe 7 Se 8 /Fe 3 (PO 4 ) 2 not only enables excellent resistance‐to‐deformation ability but also exhibits strong mechanically stable against sodiation–desodiation. Such fascinating properties combined with the accelerated Na + diffusion kinetics and enhanced electronic conductivity endowed by the 3D interconnected framework contribute to impressive cycling stability and superb rate performance for Na + ‐storage. Consequently, the designed 3D Fe 7 Se 8 /Fe 3 (PO 4 ) 2 composite with a high tap density of 0.91 cm 3 g −1 displays a stable specific capacity of 277.1 mAh cm −3 at 30 A g −1 , and outstanding long‐term cycle stability of up to 1500 cycles at 5 A g −1 without obvious capacity decay. The proposed engineering strategy and results provide new insight to design carbon‐free advanced electrodes for future practical applications.