Hierarchical Nitrogen-Doped Carbon Hosts for Low-Polarization Sulfur Cathodes in Molten-Salt Aluminum–Sulfur Batteries

Abstract

Rechargeable aluminum–sulfur (Al–S) batteries are promising candidates for low-cost and high-capacity energy storage, but their practical performance is restricted by the insulating nature of sulfur/discharge products, sluggish conversion kinetics, and structural instability of sulfur cathodes. Herein, a corn-cob-derived nitrogen-doped activated carbon host (NAC) was prepared through a one-step activation–carbonization process and used as a sulfur host for molten-salt Al–S batteries. Compared with undoped AC, NAC exhibits a wrinkled hierarchical porous structure, which promotes sulfur dispersion, facilitates ion/electron transport, and helps accommodate volume variation during cycling. Benefiting from this host structure, the S@NAC cathode delivers an initial discharge capacity of 1557 mAh g⁻¹ at 1 A g⁻¹ and retains 501 mAh g⁻¹ after 500 cycles, clearly outperforming S@AC. S@NAC also shows reduced electrochemical polarization, with a peak potential separation of 0.289 V at 1 mV s⁻¹, compared with 0.698 0.658 V for S@AC. Electrochemical impedance spectroscopy further reveals a much lower charge–transfer resistance for S@NAC. X-ray diffraction and X-ray photoelectron spectroscopy analyses support the reversible conversion between S and Al₂S₃ during discharge/charge. This work provides a feasible host-design strategy for improving sulfur conversion kinetics in molten-salt Al–S batteries.