Fullerene mixtures as negative electrodes in innovative Na-ion batteries

After the successful electrochemical intercalation of C 60 with sodium, we report here the preparation of novel negative electrodes for Na-ion batteries composed by commercial C 60 :C 70 mixture, this being significantly less expensive than pure fullerenes. An optimized solid-state Na-poly(ethylene oxide) electrolyte was used for the battery assembly. While pure C 60 electrodes show a strong irreversible behavior after the first discharge, the peculiar disordered crystalline arrangement of C 60 and C 70 in the mixture, increased by a high-energy ball milling treatment, allows to improve the specific capacity at the first discharge up to 320 mAh/g, as well as the overall reversibility.