A critical review on biochar-based engineered hierarchical porous carbon for capacitive charge storage

Hierarchical porous nitrogen-doped carbon (HPNC) nanosheets (NS) have been prepared via simultaneous activation and graphitization of biomass-derived natural silk. The as-obtained HPNC-NS show favorable features for electrochemical energy storage such as high specific surface area (SBET: 2494 m(2)/g), high volume of hierarchical pores (2.28 cm(3)/g), nanosheet structures, rich N-doping (4.7%), and defects. With respect to the multiple synergistic effects of these features, a lithium-ion battery anode and a two-electrode-based supercapacitor have been prepared. A reversible lithium storage capacity of 1865 mA h/g has been reported, which is the highest for N-doped carbon anode materials to the best of our knowledge. The HPNC-NS supercapacitor's electrode in ionic liquid electrolytes exhibit a capacitance of 242 F/g and energy density of 102 W h/kg (48 W h/L), with high cycling life stability (9% loss after 10,000 cycles). Thus, a high-performance Li-ion battery and supercapacitors were successfully assembled for the same electrode material, which was obtained through a one-step and facile large-scale synthesis route. It is promising for next-generation hybrid energy storage and renewable delivery devices.