d-π Coupling Effect for the Positive-Valent Electrochemical Reaction Acceleration in Organic Chalcogenide Cathodes

By multi-electron-involved positive-valence oxidation and negative-valence reduction, chalcogen cathodes are expected to achieve a multifold increase in capacity. Although the strategy of organic chalcogenide cathodes can promote the positive-valent state conversion of chalcogens, its slow kinetics severely hinder its application in practical electrochemical systems. In this study, we utilize the d-πcoupling effect of Fe-organic framework compounds to promote the electronic structure adjustment of chalcogens, improving the electrochemical reaction kinetics in multiple-valence states. The Fe center employs the conjugated system to mediate charge adsorption and compensation on chalcogens during electrochemical reactions. This process enhances reaction kinetics and improves the reversibility of valence transitions. As revealed by experimental characterization and theoretical simulations, the ferrocene-chalcogenide compound (Fc-S-Se) enables a three-electron transfer process, facilitated by the redox coupling between S⁺/Se⁺→S⁰/Se⁰ and S⁰/Se⁰→S^2-/Se^2-. The results show that the Fc-S-Se electrode demonstrates greater utilization of oxidation states (approximately 3 electrons transferred) and better rate performance (1400 and 391 mAh g^-1 at 0.1 and 1 A g^-1). It achieves an initial capacity of 1400 mAh g^-1 (0.1 A g^-1), approximately 3.3 times that of sulfoselenides (S-Se) (475 mAh g^-1). This discovery can inspire further exploration of multivalence active site engineering for developing advanced battery cathodes.