Breaking the Theoretical Capacity Limit of Fullerene Anode in Alkali-Ion Batteries Through Two-Dimensional Covalent...

Carbon-based anode materials offer compelling advantages for rechargeable ion batteries, and particularly fullerene C₆₀ has a higher theoretical capacity of 446 mAh g^-1 than the traditional graphite anode in lithium-ion batteries (LIBs). However, its zero-dimensional cage structure tends to spontaneously aggregate, and its alkali-metal intercalated intermediate (fulleride) facilely dissolves in organic electrolytes, severely limiting its practical anode capacity and deteriorating recyclability. Herein, for the first time, we apply metal-free two-dimensional C₆₀ covalent network (2D-C₆₀) with distinct bonding patterns, including tetragonal phase (TP-2D-C₆₀) and hexagonal phase (HP-2D-C₆₀) nanosheets, as novel anode materials for LIBs, achieving high anode capacity, breaking the theoretical limit of C₆₀ molecule. TP-2D-C₆₀ delivers a specific capacity of 522.0 mAh g^-1 at 0.1 A g^-1, outperforming HP-2D-C₆₀ (408.6 mAh g^-1) and pristine C₆₀ (3.4 mAh g^-1). This phenomenon is rationalized by DFT calculations, revealing that TP-2D-C₆₀ exhibits a higher density of Li-ion binding sites and a lower Li-ion migration barrier than HP-2D-C₆₀. To assess its universality across ion-battery chemistries, we further demonstrate the application of TP-2D-C₆₀ as an anode for sodium-ion batteries (SIBs), achieving a high discharge capacity of 309.9 mAh g^-1 at 0.1 A g^-1.