Structural regulation of coal-derived hard carbon anode for sodium-ion batteries via pre-oxidation

Hard carbon (HC) is broadly recognized as an exceptionally prospective candidate for the anodes of sodium-ion batteries (SIBs), but their practical implementation faces substantial limitations linked to precursor factors, such as reduced carbon yield and increased cost. Herein, a cost-effective approach is proposed to prepare a coal-derived HC anode with simple pre-oxidation followed by a post-carbonization process which effectively expands the d₀₀₂ layer spacing, generates closed pores and increases defect sites. Through these modifications, the resulting HC anode attains a delicate equilibrium between plateau capacity and sloping capacity, showcasing a remarkable reversible capacity of 306.3 mAh·g⁻¹ at 0.03 A·g⁻¹. Furthermore, the produced HC exhibits fast reaction kinetics and exceptional rate performance, achieving a capacity of 289 mAh·g⁻¹ at 0.1 A·g⁻¹, equivalent to ~ 94.5% of that at 0.03 A·g⁻¹. When implemented in a full cell configuration, the impressive electrochemical performance is evident, with a notable energy density of 410.6 Wh·kg⁻¹ (based on cathode mass). In short, we provide a straightforward yet efficient method for regulating coal-derived HC, which is crucial for the widespread use of SIBs anodes.