Modifier-assisted co-thermal carbonization of lignite for hard carbon with enriched pseudo-graphitic domains and closed pores toward enhanced sodium storage
Huihui Zeng, Huiyang Sun, Baolin Xing, Xiahui Gui, Qin Xu, G.S. Huang, Chuanxiang Zhang, Yuanfeng Wu, Yichao Wang, Zhengfei Chen
Abstract
Lignite, characterized by disordered aromatic lamellae, natural pores and microfractures, and surface-active functional groups, has emerged as a high-quality precursor for advanced hard carbon anodes in sodium-ion batteries (SIBs). In this work, we propose a modifier-assisted co-thermal carbonization strategy to precisely tailor the pseudo-graphitic domains and closed pores in lignite-derived hard carbons (LHC), aiming to enhance their Na + storage capabilities. Through incorporating urea during carbonization, the resulting nitrogen-doped lignite-based hard carbon (N-LHC) possesses a high content of pseudo-graphitic domains (43.6%), an optimized interlayer distance (0.373 nm), and a greater number of closed pores interconnected by short-range ordered microcrystals. Benefiting from these structural and chemical modifications, the N-LHC anode delivers a high reversible capacity of 380 mAh·g -1 , with the plateau capacity of 207 mA·g -1 and an improved initial Coulombic efficiency (ICE) of 79.1%. When paired with a NaFe 1/3 Ni 1/3 Mn 1/3 O 2 cathode, the full-cell achieves a notable energy density of 240.8 Wh·kg -1 at 20 mA·g -1 and retains 157.5 Wh·kg -1 at 200 mA·g -1 with a power density of 230.7 W·kg -1 . Electrochemical kinetics combined with ex-situ X-ray diffraction analyses reveal a synergistic sodium storage mechanism involving adsorption, intercalation, and pore filling. DFT calculations further confirm the critical role of heteroatoms doping in enhancing Na + adsorption kinetics and overall storage capacity. This work provides an effective strategy for engineering advanced hard carbon anodes toward practical high-energy-density SIBs.