N and S co-doped nanosheet-like porous carbon derived from sorghum biomass: mechanical nanoarchitecturing for upgraded potassium ion batteries

Abstract

In this study, nanosheet-like sorghum biomass is obtained by a mild alkaline treatment and high-energy ball milling. N, S co-doped hard carbon (NSSC) with the nanosheet morphology is subsequently synthesized by a direct-carbonization of the nanosheet-like sorghum biomass mixed with thiourea. NSSCs obtained at various annealing temperatures demonstrate that the optimal annealing temperature is necessary to balance the efficient heteroatom-doping and the level of carbonization. NSSC-600 obtained at the optimized annealing temperature of 600 °C presents a great K-ion storage performance as an anode material with a high reversible specific capacity of 268 mA h g⁻¹ at 100 mA g⁻¹ and outstanding stability over 2400 cycles. The effect of N and S heteroatom-doping on K-ion adsorption capacity is also verified by density functional theory (DFT) calculations.