Probing Mechanistic Insights into Highly Efficient Lithium Storage of C₆₀ Fullerene Enabled via Three-Electron-Redox Chemistry

Renewable organic cathodes with abundant elements show promise for sustainable rechargeable batteries. Herein, for the first time, utilizing C₆₀ fullerene as organic cathode for room-temperature lithium-ion battery is reported. The C₆₀ cathode shows robust electrochemical performance preferably in ether-based electrolyte. It delivers discharge capacity up to 120 mAh g^-1 and specific energy exceeding 200 Wh kg^-1 with high initial Coulombic efficiency of 91%. The as-fabricated battery holds a capacity of 90 mAh g^-1 after 50 cycles and showcases remarkable rate performance with 77 mAh g^-1 retained at 500 mA g^-1 . Noteworthily, three couples of unusual flat voltage plateaus recur at ≈2.4, 1.7, and 1.5 V, respectively. Diffusion-dominated three-electron-redox reactions are revealed by cyclic voltammogram and plateau capacities. Intriguingly, it is for the first time unveiled by in situ X-ray diffraction (XRD) that the C₆₀ cathode underwent three reversible phase transitions during lithiation/delithiation process, except for the initial discharge when irreversible polymerization in between C₆₀ nanoclusters existed as suggested by the characteristic irreversible peak shifts in both in situ XRD pattern and in situ Raman spectra. Cs-corrected transmission electron microscope corroborated these phase evolutions. Importantly, delithiation potentials derived from density-functional-theory simulation based on proposed phase structures qualitatively consists with experimental ones.