Structure reconstruction strategy for controlled pore closure via surface coating in coal-based hard carbon for enhancing sodium storage performance

Abstract

Coal-based hard carbon is considered the most promising anode material for sodium-ion batteries (SIBs) due to its low cost and high abundant resources. However, high-temperature carbonization yields a highly ordered microstructure with few closed pores, limiting sodium storage and initial Coulombic efficiency (ICE). Herein, we propose a structural reconstruction strategy utilizing liquid-phase surface coating of porous carbon with soft carbon. The pitch-derived soft carbon can coat the open pores of porous carbon, facilitating the transition from exposed to closed pores. And the coating layers characterized by a highly ordered microcrystalline structure, significantly reduce surface defects and thereby enhance the ICE. Furthermore, the improved uniform mixing of pitch solution and porous carbon promotes robust cross-linking, mitigating small molecule volatilization and increasing carbon yield. Benefiting from these increased closed pores and stable structure, the optimized BCPC-10 delivered a superior capacity of 326.7 mAh g⁻¹ with high ICE of 86.7 % and excellent cycling stability with 87.2 % retention after 100 cycles. Moreover, the assembled full-cell achieved excellent capacity retention rate of 80.1 % after 200 cycles. The proposed strategy of coating porous carbon with soft carbon undoubtedly offers a promising avenue for developing advanced coal-based anode materials for commercial SIBs.