Electrochemical intercalation of fullerene and hydrofullerene with sodium

We herein report on the ability of fullerene C60 and hydrogenated fullerene C60Hx (x~39) to operate as negative electrodes in novel Na-ion batteries. Building upon the known solubility of C60 in common organic electrolytes used in batteries, we developed a suitably optimized solid-state Na-(polyethylene oxide) electrolyte for this application. Electrochemical and structural properties of the fullerene elec trodes were investigated through cyclic voltammetry, fixed-current charge/discharge of the electrodes, impedance spectroscopy and powder X-ray diffraction. Both C60 and hydrogenated C60 have been elec trochemically intercalated with sodium. Specific capacities after the first cycle are 250 mAh g 1 and 230 mAh g 1 for C60 and C60Hx respectively. However, C60 electrode shows a strong irreversible character after the first discharge, probably due to the formation of stable polymeric NaxC60 phases, where Naþ ions diffusion is hindered. On the contrary, C60Hx displays better reversibility, suggesting that hydro genation of the buckyball could be effective to preserve sufficiently large interstitial pathways for Naþ diffusion upon intercalation.