Optimized Tap Density of Low-Cost Activated Carbon for High-Performance Supercapacitors in 18650 Cylindrical Cells

The high cost of supercapacitors relative to lithium-ion batteries is primarily attributed to the expensive activated carbon (AC) materials used in their electrodes, which can cost as much as $170–500 per kg. This study presents a cost-effective alternative by utilizing large-pellet, water filtration-grade granular activated carbon (WFG-AC) (∼$6 per kg) as an electrode material for 18650 cylindrical supercapacitor cells. Through a systematic optimization process involving ball milling, Mechano-Fusion, and annealing, we tailored WFG-AC to enhance its tap density, particle morphology, and control its oxygen content as low as possible. Unlike conventional approaches that prioritize high specific surface area, our findings reveal that tap density is the dominant factor governing electrochemical performance in volume-constrained supercapacitor designs. Despite a moderate specific surface area (886 m 2 g −1 ), WFG-AC demonstrates a high cell capacitance of 105.72 F and remarkable cycling stability (84.55% retention after 120,000 cycles), matching the performance of high-surface-area commercial ACs. These results establish WFG-AC as a scalable, cost-effective, and high-performance electrode material, providing a paradigm shift in supercapacitor electrode design while significantly reducing manufacturing costs.