Engineered high-density carbon defects enable accelerated sulfur conversion for kinetics-boosted room-temperature sodium-sulfur batteries

Abstract

The practical application of room-temperature sodium-sulfur (RT Na-S) batteries is hindered by sluggish reaction kinetics and deleterious side reactions. To address these challenges, a defective carbon is designed as a sulfur host through a simple temperature-controlled method. The abundant porosity and surface roughness enhance sulfur encapsulation and mitigate side reactions. Prominently, highly disordered structure facilitates the chemical adsorption towards NaPSs and accelerates sulfur conversion. Furthermore, electrochemical characterizations reveal that concentration polarization during the formation of long-chain NaPSs emerges as the key polarization and activation polarization dominates the nucleation of Na₂S during discharge, while they both significantly affect the formation of S₈/long-chain NaPSs during charge. Owing to the improved adsorption capability and electrocalatytic sites, S/CZ-900 presents lower concentration polarization and activation polarization during both discharge and charge. Consequently, S/CZ-900 cathode achieves 1031, 914, and 671 mAh g⁻¹ at 1, 2, and 5 C. The cathode with a high sulfur loading of 6.4 mg cm⁻² delivers an impressive areal capacity of 14.3 mAh cm⁻². Moreover, the S/CZ-900||Na/CZ-900 (Al) full cell exhibits robust cycling stability, maintaining 1094 mAh g⁻¹ after 40 cycles at 0.1 C. The insights provide a workable solution of metal-free carbonaceous host materials for the evolution of RT Na-S batteries.