Hybrid hard carbon framework derived from polystyrene bearing distinct molecular crosslinking for enhanced sodium storage

Exploiting high-performance yet low-cost hard carbon anodes is crucial to advancing the state-of-the-art sodium-ion batteries. However, the achievement of superior initial Coulombic efficiency (ICE) and high Na-storage capacity via low-temperature carbonization remains challenging due to the presence of tremendous defects with few closed pores. Here, a facile hybrid carbon framework design is proposed from the polystyrene precursor bearing distinct molecular bridges at a low pyrolysis temperature of 800°C via in situ fusion and embedding strategy. This is realized by integrating triazine- and carbonyl-crosslinked polystyrene nanospheres during carbonization. The triazine crosslinking allows in situ fusion of spheres into layered carbon with low defects and abundant closed pores, which serves as a matrix for embedding the well-retained carbon spheres with nanopores/defects derived from carbonyl crosslinking. Therefore, the hybrid hard carbon with intimate interface showcases synergistic Na ions storage behavior, showing an ICE of 70.2%, a high capacity of 279.3 mAh g⁻¹, and long-term 500 cycles, superior to carbons from the respective precursor and other reported carbons fabricated under the low carbonization temperature. The present protocol opens new avenues toward low-cost hard carbon anode materials for high-performance sodium-ion batteries.