Pyrrolic-Nitrogen-Containing Hierarchical Porous Biocarbon for Enhanced Sodium-Ion Energy Storage

Acacia auriculiformis seedpod biomass-derived activated biocarbon was generated by carbonization followed by chemical activation using KOH. The formation of the biocarbon having hierarchical porous, pyrrolic nitrogen and high surface area has been confirmed using material characterization techniques. Then, sodium-ion energy storage performances of the biocarbon was examined in the half-cell that resulted in 255 mAh g–1 as the discharge capacity at 0.1 C rate with passable rate capability and cycling stability. Further, the activated biocarbon was also tested as the electrode material for symmetric sodium-ion ultracapacitors in aqueous and non-aqueous electrolytes. The aqueous ultracapacitor exhibited an energy density of nearly 62 Wh kg−1, while the non-aqueous ultracapacitor resulted in a high specific energy of 138 Wh kg–1. When assembled in a laboratory prototype pouch cell, the activated biocarbon electrode showed a high specific energy (150 Wh kg–1) at a specific power of 1495 W kg–1. The disordered porous nitrogen-containing biocarbon associated with a high surface area leads to efficient sodium-ion storage as well as double-layer capacitance. The fabricated laboratory prototype sodium-ion ultracapacitor was practically tested to power a conventional red light-emitting diode for about 20 min on a single charge.