Fullerene mixtures as negative electrodes in innovative Na-ion batteries

[Display omitted] •New negative electrodes for Na-ion batteries based on fullerene mixture were made.•High-energy ball milling was efficient in alloying the C60/C70 molecules of the mixture.•Fullerene mixtures show better performances than pure C60 in solid-state Na-ion half cells.•Lower price of the mixture with respect to C60 is attractive for future applications. After the successful electrochemical intercalation of C60 with sodium, we report here the preparation of novel negative electrodes for Na-ion batteries composed by commercial C60:C70 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 C60 electrodes show a strong irreversible behavior after the first discharge, the peculiar disordered crystalline arrangement of C60 and C70 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.