In-situ S doping engineering of hard carbon from high sulfur coal for high-performance sodium-ion storage

Coal-based hard carbon, with superior electrochemical properties and high economic practicality, has shown great potential in the sodium-ion battery (SIB) anodes. However, limited by the intrinsic high sulfur content, the development of high-performance hard carbon anodes from high-sulfur coal has been neglected for a long time. Herein, high-sulfur coal was employed as starting precursor to prepare in-situ S-doped coal-based hard carbon through a straightforward pre-oxidation and carbonization method. Thanks to the abundant organic sulfur components in raw coal, the resulting hard carbon exhibits homogeneous S doping, optimal microcrystalline and pore structures for high-performance sodium ion storage. As expected, the in-situ engineered S-doped hard carbon anodes could deliver a large reversible capacity of 281.4 mAh·g -1 (25 mA·g -1 ), high initial Coulombic efficiency of 80.7%, good cycling stability (88.9 % capacity retention over 100 cycles) and superior rate performance (175.5 mAh·g -1 at 100 mA·g -1 ). This work not only provides novel insights on the doping engineering of coal-based carbon materials, but also uncovers new possibilities for high-performance SIB anodes.