Open-pore self-healing toward pitch-based hard carbon with optimized closed nanopores for enhanced sodium-ion battery...

Hard carbon derived from coal liquefaction pitch is a promising anode material for sodium-ion batteries due to its low cost and high carbon yield. The closed-pore structure plays a critical role in determining its sodium storage behavior. Herein, an open-pore self-healing strategy is proposed to construct closed pores in pitch-derived hard carbon. In this strategy, open pores are first generated by activation and subsequently transformed into closed pores through thermally induced carbon atomic rearrangement. The optimized sample (AZC-0.5) exhibits abundant closed pores with a volume of 0.13 cm³ g^-1 and an average diameter of 1.36 nm, which are highly favorable for sodium storage. Consequently, it delivers a reversible capacity of 357.7 mAh g^-1 at 0.1C, with a plateau capacity contribution of 249.6 mAh g^-1. The material also shows excellent rate capability and cycling stability, retaining 189.3 mAh g^-1 after 500 cycles at 5C, and achieves an energy density of 205.6 Wh kg^-1 in full-cell configurations. This work provides a viable strategy for regulating closed-pore structures in pitch-derived hard carbon and offers new insights into the structure-property relationship governing sodium storage.