Biomass-tar coated converter slag composites: A sustainable approach for high-performance supercapacitors

Converter steel slag is a significant source of solid waste, which is typically disposed of in landfills and occupies substantial land resources. Biomass tar, a byproduct of biomass thermal conversion, usually contains various toxic substances that can cause environmental harm. This study presented a co-carbonization approach of biomass tar and converter steel slag for the synergistic preparation of high-performance supercapacitor electrode materials. The material integrated a dual energy storage mechanism: the porous carbon matrix derived from biomass tar provided double-layer capacitance, while the exposed Fe₂O₃ active sites and N/O heteroatoms in the modified converter steel slag enabled pseudocapacitive effects. Among all the materials evaluated, S@TC-3 demonstrated the most outstanding electrochemical performance: achieving a remarkable specific capacitance of 333.2 F/g in a three-electrode configuration. When assembled into a symmetric device operating at 1.8 V, it delivered an energy density of 18.47 Wh/kg at a power density of 499 W/kg. Furthermore, after 10,000 charge-discharge cycles, the capacitance retention remained as high as 86.5 %. This approach achieved the value-added utilization of industrial wastes and provided a new pathway for low-cost, scalable preparation of advanced energy storage materials.