MgSO<sub>4</sub> as\nan Effective, Low-Temperature\nSulfur Dopant for Carbon Materials Enabling Fast Sodium Storage

S doping is a powerful tool to boost\nthe sodium storage performance\nof hard carbons. However, developing efficient, sustainable doping\nstrategies is still a challenge. Herein we show the effectiveness\nof MgSO<sub>4</sub> as S dopant compared to other traditionally used\nsulfates. Even at a low carbonization/doping temperature of 600 °C\nand using a low MgSO<sub>4</sub>:carbon precursor weight ratio of\n1, the glucose-based carbon material achieved a sulfur content as\nhigh as 26 wt %. This translates into a Na storage capacity of 640\nmAh g<sup>–1</sup> at 0.1 A g<sup>–1</sup> and still\n122 mAh g<sup>–1</sup> at 10 A g<sup>–1</sup>. This\nS doping tool promotes not only the redox activity at high potentials\nbut also the low potential capacity exploitable in Na-based technologies.\nIndeed, DFT studies support increased disordered induced by S doping.\nThis feature, coupled to the enhanced reversibility (ICE ∼\n77%) caused by the S doping, supports the suitability of this material\nas negative electrode in Na-based batteries and hybrid capacitors.\nFurther engineering through nanostructuring improves the kinetics\nin the usable low-potential region, which proves the beneficial effect\nof the templating technique coupled to doping. The universality of\nthe synthesis strategy is shown by successfully applying it to biomass\nproducts and wastes.