The front cover picture represents an innovative strategy for tuning the intrinsic structure of anthracite-based hard carbon via coating and heat treatment. Acetylene-derived carbon fills surface defects and transforms open pores into closed pores, while micropores form in inaccessible regions. This approach enhances initial Coulombic efficiency without relying on high-temperature carbonization for defect repair.

Hard carbon (HC) is a promising anode material for sodium-ion batteries due to its affordability, substantial sodium storage capacity, and low sodium intercalation potential. However, it suffers from low initial coulombic efficiency (ICE). Herein, an innovative acetylene-mediated strategy is proposed to tailor the heteroatom content and pore structure of anthracite-derived HC. During pyrolysis, hydrogen radicals from acetylene react with heteroatoms (O, N, S) in anthracite, eliminating them as gaseous species (e.g., H₂O, NH₃, H₂S), while carbon radicals deposit into defects, converting open pores into closed pores. Compared to HC produced through direct anthracite carbonization, the optimized anthracite-based HC demonstrates superior electrochemical performance, delivering a high specific capacity of 220 mAh g⁻¹ at 0.3C with 88% ICE. Furthermore, the material exhibits exceptional cycling stability, maintaining a reversible discharge capacity of 210 mAh g⁻¹ at 0.3C after 500 cycles. This radical-mediated approach simultaneously mitigates irreversible Na⁺ consumption and boosts capacity, surpassing the typical ICE limit (70%–85%) of HCs. The method provides a universal route for designing high-performance carbon anodes from diverse precursors.