Abstract:

Hard carbon is widely regarded as one of the most commercially promising anode materials for sodium-ion batteries. Nevertheless, its practical application remains challenged by limited reversible capacity and sluggish sodium storage kinetics. Herein, a strategy is proposed to modify N doped hard carbon by introducing Co to construct CoN_x sites (Co-NC). In Co-NC, the CoN_x sites provide sufficient active sites for Na storage, leading to an enhanced reversible capacity of 422.8 mAh g⁻¹ at 0.05 C. Meanwhile, Co-NC exhibits excellent initial Coulombic efficiency, rate capability and cycling stability. Multiple characterization results confirm that the CoN_x sites facilitate the formation of a solid electrolyte interphase enriched in inorganic components, which can accelerate ion transport kinetics at the electrode electrolyte interface. Furthermore, in situ and ex situ analyses were conducted to elucidate the structural evolution of Co-NC across different sodium storage stages, as well as the dynamic evolution pathway of the CoN_x sites. This work offers a viable strategy to concurrently enhance the capacity and kinetic performance of hard carbon anodes.

Key words: Sodium-ion batteries, Hard carbon, Active site, Solid electrolyte interface