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.