Flash upcycling waste activated carbon into high-performance sodium-ion anodes via joule heating: Dual regulation of microcrystals and pore configuration

The reuse of Waste Activated Carbon (WAC) faces inherent challenges: even after impurity removal, the collapsed pore structure still significantly reduces its adsorption efficiency. When applied as anode materials for high-performance Sodium-Ion Batteries (SIBs), their intrinsically disordered structure and unsuitable pore configuration further limit the electrochemical performance. This study proposes using Flash Joule Heating (FJH) to instantaneously treat WAC, achieving simultaneous “graphite-like carbon microcrystalline domain expansion” and “pore reconstruction” within seconds, thereby transforming “small pore entrances with large cavities” into “large pore entrances with small cavities”. XRD/TEM analyses confirmed that FJH treatment generated abundant graphite-like microcrystalline structures (La≈4.77 nm). BET analysis revealed the pore entrance expanded from 5.72 nm to 6.66 nm, while the cavity volume decreased from 0.098 cm³ ∙g⁻¹ to 0.068 cm³ ∙g⁻¹. This long-range ordered graphene-like microcrystalline layered structure significantly enhances the plateau capacity. Meanwhile, the open-pore structure with larger pore size and smaller pore volume effectively accommodates stress from repeated Na⁺ insertion/extraction, preventing pore collapse. The optimized wac_40a electrode demonstrated a significant improvement in reversible capacity from 161.9 mAh∙g⁻¹ to 374.7 mAh∙g⁻¹ (0.01–2.0 V, 25 mA∙g⁻¹), with plateau capacity contribution increasing from 22.9 % to 57.0 %. It maintained 92.70 % capacity retention after 1700 cycles at 200 mA∙g⁻¹. This work pioneers a novel pathway for value-added utilization of WAC and fabrication of high-performance SIBs anodes.