Tightly-connected carbon-coated FeS₂ hollow sphere-graphene microstructure for ultrafast and stable potassium ion storage

Conversion-type pyrite (FeS2) is a promising anode material for potassium-ion batteries (PIBs) due to its low cost and superior capacity. However, its poor rate capability and unsatisfactory cycling performance impede advances towards industrial applications. Herein, a tightly-connected carbon-coated FeS2 hollow sphere-graphene microstructure (C-HS-FeS2@rGO) is proposed to address these challenges. The material is custom designed with FeS2 hollow spheres to enable unobstructed electrolyte penetration for high capacity, and a tight FeS2/graphene connection by dopamine-derived interfacial carbon to realize fast charge transfer and outstanding structural stability of FeS2. Thanks to these structural features, C-HS-FeS2@rGO exhibits outstanding rate performance (similar to 200 mA h g(-)(1) at 10 A g(-)(1)) and excellent cycling stability (130 mA h g(-)(1) even after 5000 cycles at 5 A g(-)(1)), which exceeds the performance of graphene-wrapped hollow-sphere FeS2 (HS-FeS2@rGO) and hollow-sphere FeS2 (HS-FeS2). The capacitive-dominated potassiation/de-potassiation process and robust solid electrolyte interface (SEI) layer with negligible cracks and inorganic-KF-salt-dominated compositions are revealed by mechanism study and advanced microscopy analysis. K-ion full cells using C-HS-FeS2@rGO as anode and Prussian blue as cathode are assembled to demonstrate its practical application potential. This work provides new approach for custom design of microstructured FeS2 anode for high-performance PIBs.