Deashing Strategy on Biomass Carbon for Achieving High-Performance Full-Supercapacitor Electrodes

The porous carbon materials, namely, MC700/800, PC700/800, and SC700/800, have been prepared using several biomasses (mushroom dreg, Chinese parasol leaves, and Siraitia grosvenorii leaves) as individual precursors at 700 and 800 °C activation temperatures. Among these carbon-negative electrodes, SC700 exhibits an impressive specific capacitance, nearly 2-fold that of commercial activated carbon (169.5 F g^-1). When assembled with a Ni(OH)₂ positive electrode in asymmetric supercapacitors, the SC700//Ni(OH)₂ device can achieve a specific capacitance of 80 F g^-1 and an energy density of 32.16 Wh kg^-1 at 1700 W kg^-1. In contrast, the MC700 electrode can display inferior performance potentially attributed to the high ash content in the biomass. To further optimize the activated process of the MC700 product, three deashing carbon negative electrodes (denoted as MC(H₂O), MC(HF), and MC(Mix)) were prepared by deashing treatment using H₂O, HF, and mixed acid, and then a modified composite positive electrode (MC700@MnO₂(MCM)) has been prepared by doping with MnO₂. Electrochemical testing demonstrates that the deashing strategy achieves a significant capacitance enhancement compared to the primary carbon material while maintaining excellent cyclic stability. The asymmetric supercapacitors, assembled from these decorated electrode materials, exhibited a maximum energy density of 21.08 Wh kg^-1 and a power density of 1150 W kg^-1 under a high-voltage window of 2.2 V. Additionally, this type of full device can power 28 LEDs for approximately 5 min.