Modifying lignite-derived hard carbon with micron carbon tubes to improve sodium-ion storage

Lignite is a feasible raw material for the development of hard carbon anodes for sodium-ion batteries because of its high abundance and cheap cost. However, the existence of more defects in lignite-derived carbon, leads to unsatisfactory electrochemical performance as the anode of sodium-ion batteries, such as the initial Coulombic efficiency (ICE) and capacity retention rate. In this work, we introduce a preparation process of lignite-derived hard carbon using carbonized lignite and oleic acid (C9H16O2) as precursors. The micron carbon tubes (MCTs) generation on the hard carbon surface can provide additional Na+ active sites and reduce the defects, which effectively enhances the specific capacity and ICE of the anode. Benefiting the MCT modification, the hard carbon anode has a high reversible capacity of 244.8 mAh g−1 and ICE of 76.72%, which is respectively 30% and 10% higher than that of the bare hard carbon anode, this is of significance for the practical application of coal-based hard carbon in sodium-ion batteries.