Electrochemical intercalation of fullerene and hydrofullerene with sodium

We herein report on the ability of fullerene C60and hydrogenated fullerene C60Hx(x∼39) to operate as negative electrodes in novel Na-ion batteries. Building upon the known solubility of C60in 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 electrodes were investigated through cyclic voltammetry, fixed-current charge/discharge of the electrodes, impedance spectroscopy and powder X-ray diffraction. Both C60and hydrogenated C60have been electrochemically intercalated with sodium. Specific capacities after the first cycle are 250 mAh g−1and 230 mAh g−1for C60and C60Hxrespectively. However, C60electrode shows a strong irreversible character after the first discharge, probably due to the formation of stable polymeric NaxC60phases, where Na+ions diffusion is hindered. On the contrary, C60Hxdisplays better reversibility, suggesting that hydrogenation of the buckyball could be effective to preserve sufficiently large interstitial pathways for Na+diffusion upon intercalation.