Conversion-driven heterointerface reconfiguration enables fast ion migration in iron disulfide/sulfur-based positive...

Establishing stable active sites and molecular-scale bridging architectures at electrode-electrolyte interfaces is essential for advancing fast-charging batteries, yet remains challenging because the principles governing interfacial reaction networks and materials design are not fully understood. In sulfur-based electrodes, irreversible sulfur-cluster dissolution and progressive interfacial degradation severely limit capacity retention and cycling stability. Here we show that reversible dynamic covalent tethering can be constructed at electrified interfaces by coupling hierarchically structured FeS₂ with exogenous sulfur clusters. During the initial full discharge, Cu²⁺ ions are spontaneously reduced and reconstruct the interface to form a Cu₂S/FeS₂ heterostructure, in which interfacial Fe-S-Cu bonds act as ordered covalent bridges. This surface-bound Fe-S-Cu bridging topology reduces interfacial resistance, accelerates charge-transfer kinetics and suppresses metastable phase formation arising from incomplete conversion. Copper ions further function as molecular rivets, preferentially depositing at edge sites and directionally bonding with sulfur atoms to stabilize the FeS₂-hosted sulfur redox system. This dynamic bonding framework preserves the structural coherence of the FeS₂ matrix while immobilizing polysulfide intermediates, enabling more than 68,000 charge-discharge cycles at 100 A g^-1. Our findings establish a molecular-level design strategy that links atomic bonding motifs with macroscopic electrochemical functionality.