Supercapacitors find numerous applications such as in consumer electronics, peak power demands, capturing surge power, etc. Various types of carbon materials are explored as electrode material. In this work, disordered mesoporous carbon was synthesized from expired medicinal capsule covers by sulfonation and subsequent chemical activation was carried out with KOH. Powder X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, Brunauer−Emmett−Teller studies, and X-ray photoelectron spectroscopy were utilized to characterize the generated carbon which confirmed the disordered carbon had a large surface area with stratified pores. The testing for electrochemical charge storage was conducted on a three-electrode setup comprising an aqueous 1 M NaClO 4 electrolyte that exhibited a high 324 F g −1 specific capacitance at 0.4 A g −1 , revealing suitability for sodium-ion ultracapacitor. Consequently, CR2032 coin-type sodium-ion capacitors were fabricated using both aqueous and nonaqueous electrolytes. The laboratory prototype capacitor with the aqueous electrolyte delivered 42 Wh kg −1 specific energy at 179 W kg −1 specific power. Besides, the capacitor with the nonaqueous electrolyte showed a remarkable 54.3 Wh kg −1 specific energy at 540 W kg −1 specific power. The Coulombic efficiency exhibited by both devices was about 99% even at the 10000th charge−discharge cycle. The amplified charge storage performance of the disordered carbon was ascribed to the presence of homogeneous mesopores that led to enhanced accessibility of the electrode/electrolyte contact area. According to the results of the power law and Dunn's approach, the mesoporous carbon electrode was found to have a considerable diffusive charge storing mode involving Na + intercalation in the sodium-ion nonaqueous ultracapacitor. A green-light-emitting diode could run continuously for 16 min on a single charge using the laboratory prototype CR-2032 coin-type nonaqueous ultracapacitor. Interestingly, a homemade solid-state flexible sodium-ion ultracapacitor was also fabricated that impressively manifested 13.7 Wh kg −1 specific energy at 180 W kg −1 specific power in 180°bent angle.

The cassava-peel biomass-derived self-heteroatomenriched 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 m 2 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.

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