Sulfur-Mediated Dehydrogenation and Bonding for Plateau-Dominated Hard Carbon Anodes.

Developing a carbon anode with high performance but low cost is one most pivotal challenges for the commercialization of sodium ion batteries (SIBs). Therefore, an sulfur-mediated solid-state approach is proposed to form 3D crosslinked polymer networks in a pitch precursor and then achieve elaborate microstructures for effective sodium storage. Sulfur-linked structures interfere with the stacking regularity of carbon layers, thereby eliminating the graphitic transformation of pitch at high treatment temperatures, expanding interlayer distances, and promoting the development of closed pores. Consequently, sodium storage capacity in such carbon material is impressively augmented from 109 to 315 mA h g^-1, with a plateau contribution exceeding 81.3% at low voltages, which can improve energy density of SIBs. Compared to prior Oxygen-related methodologies, this sulfur-mediated technique not only offers a more scalable strategy but also achieves superior plateau performance at lower carbonization temperatures (≈1300 °C), far below the conventional threshold of 1500 °C. Additionally, comprehensive testing demonstrates that sodium storage operates via an "adsorption-intercalation-pore filling" mechanism, with closed nanopores playing a crucial role in enabling efficient Na storage through pore filling in the low voltage region. This work also presents a scalable strategy for the development of high-performance carbon anode materials from low-cost pitch.