Deep oxygen-crosslinking and self-coating synergetic engineering on pitch-based hard carbon anode for sodium-ion batteries.

Low softening-point pitch (LP) is regarded as a promising precursor for hard carbon anodes in sodium-ion batteries due to its low cost and high yield. However, the sodium storage performance of LP-derived carbon materials is always undesirable owing to the high degree of graphitization. Herein, a self-coated hard carbon (HC@SC) material with relative disordered structure was developed from LP precursor using synergistic deep pre-oxidation and self-coating strategies. The oxygen-crosslinked structure endowed in the deep pre-oxidation process effectively hinders carbon layer growth during the subsequent pyrolysis, promoting the formation of disordered hard carbon structure with larger interlayer spacing. Additionally, the soft carbon self-coating layer is introduced onto the hard carbon surface to improve its electrical conductivity and then enhance the sodium diffusion. Consequently, the HC@SC anode delivers an initial charge capacity of 311.9 mAh g at 0.05 A g and a rate capability of 109.7 mAh g at 5 A g, and preserves a high-capacity retention of 90.0 % after 1000 cycles at 1 A g. Furthermore, the NNMO//HC@SC full cell exhibits desirable cycling stability and rate performance.