Activated porous carbon materials with ultrahigh specific surface area derived from banana peels for high-performance lithium–sulfur batteries

A series of banana peels derived porous carbon (BPPC) materials were fabricated by pyrolysis carbonization with different numbers of KOH activation. The Brunauer–Emmett–Teller tests indicated the number of activation effectively improves the specific surface area and pore volume of the BPPC. Amongst, the BPPC-2 (activated twice) possesses ultrahigh specific surface area (2044.57 m² g⁻¹) and large pore volume (2.40 cm³ g⁻¹) on account of the improved hierarchical porous microstructure. After S loading process, the resultant C/S composites were introduced as cathode material in Li–S batteries. The S/BPPC-2 composite cathode exhibited a higher initial specific capacity (1481.54 mAh g⁻¹ at 0.1 C) and a better reversible capacity (351 mAh g⁻¹ after 300 cycles at 1 C) than those of others. It also exhibited excellent high rate performance even at 5 C. The enhanced electrochemical performances were ascribed to the improved specific surface area and larger pore volume of the BPPC-2, which effectively facilitated the intimate contact between sulfur and the conductive matrix, accommodating severe volume change. Besides, the micro/mesopores provided high adsorption power to inhibit the dissolution of polysulfides. This research suggested that the activation number played a key role in improving the electrochemical performance of composite cathode in Li–S batteries.