Covalent Bridges Enabling Layered C60 as an Exceptionally Stable Anode in Lithium-Ion Batteries.

Fullerene (C60) exhibits rich redox chemistry but suffers from severe dissolution of reduced fulleride species in carbonate electrolytes, leading to poor reversibility and rapid capacity fading. Here, we demonstrate covalent bridging as a general strategy to stabilize the fullerene framework using Mg4C60. Mg atoms promote intercage covalent connections through C-C single bonds and [2 + 2] cycloaddition bonds, transforming a van der Waals molecular solid into a layered polymeric framework. Comprehensive characterizations reveal that such bridging effectively suppresses dissolution, preserves structural integrity, and enables a reversible Li+ storage process. Interestingly, unlike pristine C60 that undergoes multiple phase transitions, Mg4C60 exhibits slope-type electrochemical profiles reminiscent of soft carbon yet originates from an ordered two-dimensional framework. Comprehensive mechanistic studies reveal reversible fullerene cage distortions accompanied by the dynamic reconstruction of sp2 electronic states, while the covalently bridged scaffold remains intact. This work establishes covalently bridged fullerenes as a new class of durable carbonaceous anodes and provides a general pathway for designing ordered carbon frameworks with enhanced stability for next-generation rechargeable batteries.