Engineering optimization of tea waste–derived activated carbon/graphite composites for supercapacitors

ABSTRACT Activated carbon derived from tea waste is a sustainable candidate for supercapacitor electrodes, however, its practical application is often constrained by limited electrical conductivity. In this study, tea waste–derived activated carbon prepared via environmentally benign K₂CO₃ activation was combined with graphite as a conductive additive to examine engineering trade-offs between porosity and electrical conductivity. Activated carbon–graphite composites with varying graphite contents were systematically characterized. The activated carbon exhibited a specific surface area of 853 m² g⁻¹, while electrical conductivity increased from 1.43 to 14.96 S cm⁻¹ with increasing graphite content. Electrochemical performance was evaluated using symmetric supercapacitor cells assembled in a cylindrical 18650 configuration with 1 M Na₂SO₄ electrolyte. Among the investigated compositions, the composite containing 20 wt.% graphite showed the most balanced performance, delivering a specific capacitance of 89.62 F g⁻¹, an energy density of 17.92 Wh kg⁻¹, and a power density of 35.29 W kg⁻¹, together with reduced internal resistance. Cycling tests showed a capacitance retention of 74.6% after 4000 cycles at 1 A g⁻¹, indicating acceptable durability for biomass-derived carbon electrodes evaluated in practical full-cell configurations. Overall, this work highlights an application-oriented engineering optimization strategy for tea waste–derived carbon/graphite composites in practical supercapacitor cells.