Superionic Conductivity in the Li4C60 Fulleride Polymer

We report on the extraordinary superionic conductivity in the fulleride polymer ${\mathrm{Li}}_4{C}_{60}$ , a crystalline material with no disorder. $7\mathrm{Li}$ , NMR, and dc/ac conductivity show uncorrelated ionic hopping across small energy barriers ($\Delta E_a\sim 200\mathrm{meV}$ ) and an ionic conductivity of ${10}^{-2}S/\mathrm{cm}$ at room temperature, higher than in “standard” ionic conductors. Ab initio calculations of the molecular structure find intrinsic unoccupied interstitial sites that can be filled by ${\mathrm{Li}}^{+}$ cations in stoichiometric ${\mathrm{Li}}_4{C}_{60}$ even at low temperatures. The low energy required for the occupation of these sites allows a sizable ${\mathrm{Li}}^{+}$ diffusion above 130 K. The results suggest novel application of lithium intercalated fullerides as electrodes in Li ions batteries.

Reproduced with permission. Copyright 2009, American Physical Society