Magnesium-induced sulfur fixation strategy for the preparation of high-sulfur doped carbon with superior Na storage performance

Abstract

Sulfur (S) doping is recognized as a robust strategy to improve the Na⁺ storage property of carbon electrode. However, designing novel and effective S-doping method that combines safety, economy, and high doping levels remains urgent and challengeable. Herein, magnesium (Mg) salt is found to present an effective S-fixation role, including the Mg–S strong interaction promoted thermal stability of S atoms and the secondary S doping of MgSO₄-derived SO₂. Based on this S fixation strategy, a novel hard carbon with high S doping level of 16.5 wt% is fabricated by using sulfonated magnesium gluconate as raw material. This S-doped carbon anode delivers a high reversible Na storage capacity of 424 mAh g⁻¹ at 0.1 A g⁻¹, and after 1000-time cycling test under 1 A g⁻¹, the specific capacity remains 249 mAh g⁻¹ with a capacity retention rate of 90 %.