The Elastic Covalent Polycysteine Crosslinked Binary Hollow FeS₂ Nanospheres for Highly Reversible Sodium Storage

Abstract The high irreversibility to FeS 2 ‐based anode thwarts its applicability in sodium ion batteries (SIBs), originally stem from the sluggish Na + insertion/extraction kinetics, confined by the high desolvation barrier, the thick electric double layer (EDL) and the long transport routine inside FeS 2 . Herein, the covalent polypeptide oligomers (Pcy) based on cysteine (Cy) with β‐sheet configuration grafted binary hollow carbon coupled FeS 2 @Fe 2 O 3 heterostructure, i.e., FeS 2 /Fe 2 O 3 @C@Pcy, are designed to achieve low desolvation barrier, the contracted EDL via weakened coulombic interaction stems from the zwitterionic feature and enhanced Na + transport capacity inside FeS 2 . The semi‐interpenetrating oligomers possessing a weak coordination environment, massively accelerate the desolvation kinetics, additionally, the orderly and dense vertical occupation within the inner Helmholtz plane (IHP) also enormously reduces thickness of EDL. The binary hollow structure complex possessing typical ion looping routine considerably expedites the Na + transport kinetics inside anode. Both experimental and theoretical trials demonstrate such FeS 2 composite manifests a high reversibility in Na + storage in virtue of exceptional structure stability, rapid ion transport kinetics, and swift reaction kinetics.