Inherent Heteroatom-enriched Amorphous Carbon as High-performance Electrode for Sodium-ion Battery and Sodium-ion Ultracapacitor

The cassava-peel biomass-derived self-heteroatom-enriched disordered carbon was synthesized by means of carbonization followed by chemical activation using KOH. The obtained carbon was characterized using X-ray diffraction (XRD) and Raman and Fourier-transformed infrared (FT-IR) spectroscopic studies. The XRD study and Raman results revealed the highly disordered nature of the derived carbon. Morphological features of the sample were confirmed using scanning electron microscopy and high-resolution transmission electron microscopy analyses. It was observed that the disordered carbon had slit-type pores with a high surface area of 1032 m2 g−1. The X-ray photoelectron spectroscopy analyses confirmed that the disordered carbon was enriched with self-doped heteroatoms (N, O, S). Sodium-ion half-cell battery was fabricated using the cassava-peel biomass-derived disordered carbon as an anode that exhibited a high discharge capacity of 490 mA h g–1 and stabilized at 355 mA h g–1 at a 0.1 C-rate with excellent rate capability and reversibility. Further, the disordered biocarbon was examined for symmetric sodium-ion ultracapacitors in both aqueous and non-aqueous electrolytes. The aqueous symmetric sodium-ion ultracapacitor exhibited a high specific energy of 120 W h kg–1 at a specific power of 118 W kg–1, while the non-aqueous symmetric sodium-ion ultracapacitor exhibited a high specific energy of 160 W h kg–1 at a specific power of 425 W kg–1. The symmetric non-aqueous device exhibited almost 100% coulombic efficiency even after 10,000 cycles. The enhanced sodium-ion energy density was attributed to the hierarchical pores and self-doped heteroatoms that promoted diffusive mode of sodium storage, as confirmed by Dunn’s method as well as Power law. A laboratory prototype non-aqueous sodium-ion ultracapacitor in the form of CR-2032 coin cell was demonstrated to power a commercial red color LED bulb for more than 10 min on single charge.