Waste Biomass as in Situ Carbon Source for Sodium Vanadium Fluorophosphate/C Cathodes for Na-Ion Batteries

This work presents a series of electrode materials constituted by a sodium vanadium fluorophosphate as the electroactive phase and an in situ generated carbon derived from waste biomasses as carbon source. The waste biomasses consist of grounded vine-shoots, eucalyptus wood, and sucrose as control sample. The materials were obtained by hydrothermal carbonization during the hydrothermal synthesis followed by a flash thermal treatment (FTT). This way, carbonaceous matter decomposes into hydrochar while the electroactive phase is formed under autogenous pressure at 170 or 200 °C. The electrochemical tests were performed by adjusting the electrode composition to a total carbon amount of 20 wt %, so that the suitability of the in situ carbon as conductive additive was evaluated. Electrochemical performance was significantly improved after an FTT treatment. Among the biomass-based materials, samples that had the highest amount of the in situ generated carbon, resulting from eucalyptus biomass, showed the best e...