Core–Shell Structured Fe₇S₈@C Nanospheres as a High-Performance Anode Material for Potassium-Ion Batteries

Fe₇S₈, a potential anode material, has been extensively investigated but still faces challenges because of its poor cycling performance resulted from a large volume expansion. In this work, a solvothermal approach was employed to synthesize quasicubic α-Fe₂O₃ nanoparticles followed by sequential phenol-formaldehyde resin and mesoporous SiO₂ coating. After sulfurization and the subsequent removal of the SiO₂ shell, a Fe₇S₈@medium thickness carbon coating has been successfully fabricated, which exhibits a large specific capacity, remarkable high-current property, and stable cyclic performance for potassium-ion batteries (PIBs). It delivers a 423.3 mAh g^–1 superior initial reversible capacity at 0.2 A g^–1, excellent rate performance of 212.6 mAh g^–1 at 2 A g^–1, and long cyclic life of 266.9 mAh g^–1 at 1 A g^–1 after 500 cycles. These remarkable potassium storage properties are related to the excellent stress self-cushioning effect due to the spherical nanoarchitecture and complete carbon covering.