River driftwood pretreated via hydrothermal carbonization as a sustainable source of hard carbon for Na-ion battery anodes

Producing hard carbon from lignocellulosic biomass has been the focus of recent studies as a promising source of anode material for Na-ion batteries. Woody biomass is a potential source, but it is already well valorized. Consequently, river driftwood can be an excellent alternative, especially since it is a disturbing waste for dam regulators. It can jeopardize dam safety, damage intake works, and sink in reservoirs, lowering water quality and decreasing reservoir volume. We examine the potential of river driftwood as a source of hard carbon for Na-ion batteries. Hydrothermal carbonization (HTC) was carried out at temperatures between 180 and 220 °C as the first step to produce hydrochar followed by an upgrading pyrolysis step at 1400 °C under an inert atmosphere to obtain hard carbon. We investigated the effect of HTC operational conditions and driftwood biomass (genera) on hydrochar and hard carbon properties, as well as the latter's impact on Na-ion batteries. The produced carbon electrodes delivered a reversible capacity of 270–300 mAh·g^-1 for the first cycle and showed high coulombic efficiencies of 77–83%. We also observed promising cyclability of a maximum 2% loss after 100 cycles. Moreover, results suggest that obtained hard carbon can compete with commercial materials and is capable to supply large battery factories with anode material.