C–Na–O electrostatic interactions boost the kinetics of coal-derived hard carbon anodes for high-performance sodium-ion batteries

Abstract

Coal-derived hard carbon is a highly promising anode material for sodium-ion batteries (SIBs); however, its inherent structural disorder, limited porosity, and sluggish ion transport kinetics severely restrict its electrochemical performance. To address these challenges, this study introduces C–Na–O interaction motifs via the co-pyrolysis of Xinjiang bituminous coal with glucose and sodium carbonate. The resulting hard carbon exhibits excellent electrochemical performance, delivering a high reversible capacity of 299.8 mA h g⁻¹, an initial coulombic efficiency of 90.46%, and a retained capacity of 217 mA h g⁻¹ after 800 cycles at 0.2 A g⁻¹. Galvanostatic Intermittent Titration Technique (GITT) measurements and in situ Raman spectroscopy reveal the Na⁺ storage mechanism. Density functional theory (DFT) calculations demonstrate that, following oxygen incorporation, Na is adsorbed through synergistic interactions with carbon and oxygen atoms to form C⋯Na–O and C–Na–O configurations. Among them, the C–Na–O structure facilitates Na⁺ storage and diffusion, while the C⋯Na–O configuration contributes to enhancing the initial coulombic efficiency. This work presents a structurally integrated and scalable strategy for constructing fast-ion-conducting channels in coal-based hard carbon, offering new mechanistic insights and practical guidance for the development of high-performance and sustainable SIB anode materials.