Core–Shell Structured Fe 7 S 8 @C Nanospheres as a High-Performance Anode Material for Potassium-Ion Batteries

Fe 7 S 8 , 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-Fe 2 O 3 nanoparticles followed by sequential phenol-formaldehyde resin and mesoporous SiO 2 coating. After sulfurization and the subsequent removal of the SiO 2 shell, a Fe 7 S 8 @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.