Rationally designing surface structure by CoN active site to evoke sodium storage sites of hard carbon

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. CoN x active sites facilitate fast sodium storage kinetics and promote the formation of an inorganic-rich solid electrolyte interphase. • Co-modified N-doped hard carbon (Co-NC) achieves a high reversible capacity of 422.8 mAh g −1 . • Designing CoN x surface structures provides abundant active sites for sodium storage. • CoN x active sites facilitate the formation of an inorganic-rich solid electrolyte interphase. • Co-NC exhibits excellent rate capability and improved initial Coulombic efficiency.