Controllable hierarchical porous FeSe2 with excellent long cycle lifespan as anode materials for sodium-ion battery

Transition metal selenides are regarded as most promising anode materials for sodium ion battery (SIB) due to their high theoretical specific capacity and environment benignly. Yet the severe volume expansion and sluggish kinetics during cycling leading to capacity fading and material pulverizing restrict its application in SIB. Herein, iron selenides (N-FeSe2) with controlled porous structure is synthesized via facile salt template-assisted method. When N-FeSe2 with hierarchical pore structure serves as anode materials for SIB, a highly reversible capacity of 520.4 mA h g-1 is maintained at 1 A g-1 after 100 cycles. Even at 10 A g-1, the capacity still remains 333 mA h g- 1 after 1800 cycles, which shows extraordinary cycle stability. In addition, N-FeSe2 provides excellent diffusion coefficient and high initial Coulomb efficiency (78.9 %), which is attributed to its special hierarchical porous structure and intrinsic pseudocapacitance characteristics. DFT calculations indicate that an increase in vacancy concentration enhances the conductivity of the material, thereby improving its dynamic performance. In this work, a simple and universal synthesis method is developed, and the pore structure and morphology of the final product can be controlled by simple parameter regulation.