Low-dimensional Li+ ion dynamics in the lithiated Buckminster fullerene Li4C60

Lithiated Buckminster fullerene (Li 4 C 60 ) has recently been identified as a fast Li + ion conductor. Here, we present a comprehensive NMR-based analysis of 7 Li dynamics in Li 4 C 60 . Our findings indicate that long-range lithium hopping is to be characterized by an activation energy of 0.26 eV. At 378 K, the Li + jump rate turned out to be in the order of 10 9 s −1 , which translates into Einstein-Smoluchowski diffusion coefficients D ranging from ca. 2 to 5 × 10 −7 cm 2 s −1 , depending on the jump distance chosen (3.6–5 Å) to convert the jump rate into D . The corresponding Arrhenius pre-factor reaches 3 × 10 12 s −1 and lies in the range of typical phonon frequencies. Comparing our relaxation rates with those presented in the literature earlier suggests low-dimensional Li + diffusion in Li 4 C 60 . For short-range or localized Li + jump processes, presumably governed by motional correlation effects, we find much lower activation energies ranging from 0.08 eV to 0.17 eV. • Fast Li + ion dynamics in Li 4 C 60 (0.26 eV) characterized by a Li residence time of 1 ns at 376 K. • Arrhenius pre-factor takes values typically seen for phonon frequencies. • Short-range Li + motions are governed by even lower activation energies (0.08 eV to 0.17 eV).