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.