CaCl2-induced pore–heteroatom synergy via microwave activation for supercapacitor carbon

Preparation of high-performance porous carbons from biomass precursors for supercapacitor electrode materials is challenged by their inherent rigid lignocellulosic structure, which hinders the precise control of pore architecture and effective heteroatom doping. This study proposed a novel two-step strategy utilizing CaCl 2 preactivation synergistically combined with microwave-assisted secondary activation to overcome those challenges. Experimental results show that, the CaCl 2 preactivation optimized the pore distribution and increased 39.3% nitrogen doping of materials, because Ca 2+ disrupts cellulose hydrogen bonding and promotes depolymerization. Density Functional Theory (DFT) calculations confirm that these nitrogen doping sites enhance K + adsorption capacity. Benefiting from this abundant N-doping and the rich sites induced on mesopores and micropores, the resulting SJ-KOH electrode achieved a high specific capacitance of 338.92 F/g (at 0.5 A/g) in a three-electrode system. The assembled symmetric supercapacitor device exhibited 264.10 F/g (at 0.25 A/g), a high energy density of 9.15 Wh/kg (at 62.35 W/kg), and maintained 6.18 Wh/kg even at a high power density of 4906.73 W/kg. Furthermore, it demonstrated excellent stability with 91.73% capacitance retention after 17,500 cycles (at 10 A/g). Mass production analysis indicates SJ-KOH exhibits the lowest cost per stored capacitance and superior performance over single-step (J-KOH) or conventional two-step (FJ-KOH) activations. This work would provide a feasible and cost-effective pathway to improve doping performance when producing high-performance carbon-based energy storage materials from biomass waste.