Deashing Strategy\non Biomass Carbon for Achieving\nHigh-Performance Full-Supercapacitor Electrodes

The porous carbon materials, namely, MC700/800, PC700/800,\nand\nSC700/800, have been prepared using several biomasses (mushroom dreg,\nChinese parasol leaves, and Siraitia grosvenorii leaves) as individual precursors at 700 and 800 °C activation\ntemperatures. Among these carbon-negative electrodes, SC700 exhibits\nan impressive specific capacitance, nearly 2-fold that of commercial\nactivated carbon (169.5 F g<sup>–1</sup>). When assembled with\na Ni(OH)<sub>2</sub> positive electrode in asymmetric supercapacitors,\nthe SC700//Ni(OH)<sub>2</sub> device can achieve a specific capacitance\nof 80 F g<sup>–1</sup> and an energy density of 32.16 Wh kg<sup>–1</sup> at 1700 W kg<sup>–1</sup>. In contrast, the\nMC700 electrode can display inferior performance potentially attributed\nto the high ash content in the biomass. To further optimize the activated\nprocess of the MC700 product, three deashing carbon negative electrodes\n(denoted as MC(H<sub>2</sub>O), MC(HF), and MC(Mix)) were prepared\nby deashing treatment using H<sub>2</sub>O, HF, and mixed acid, and\nthen a modified composite positive electrode (MC700@MnO<sub>2</sub>(MCM)) has been prepared by doping with MnO<sub>2</sub>. Electrochemical\ntesting demonstrates that the deashing strategy achieves a significant\ncapacitance enhancement compared to the primary carbon material while\nmaintaining excellent cyclic stability. The asymmetric supercapacitors,\nassembled from these decorated electrode materials, exhibited a maximum\nenergy density of 21.08 Wh kg<sup>–1</sup> and a power density\nof 1150 W kg<sup>–1</sup> under a high-voltage window of 2.2\nV. Additionally, this type of full device can power 28 LEDs for approximately\n5 min.