Locally Curved Surface with CoN4 Sites Enables Hard Carbon with Superior Sodium‐Ion Storage Performances at −40 °C

The impressive electrochemical performance of sodium‐ion batteries at low temperatures has long been recognized as a promising technical advantage. However, the inadequate transport kinetics of Na+ ions and complex interfacial reactions at the hard carbon anode surface hinder the practical implementation of commercial sodium‐ion batteries. Herein, a novel approach to address this issue by introducing a homogenized functional carbon coating layer with a locally curved configuration is proposed. This coating layer is designed to accommodate single CoN4 sites on the surface of commercial hard carbon particles, resulting in enhanced sodium storage performance at low temperatures. The surface‐modified hard carbon anode material (HC‐Z1) demonstrates a commendable rate performance of 220.6 mAh g−1 at 3 A g−1@25 °C and a substantial reversible capacity of 288.7 mAh g−1 with an 89% capacity retention at 0.06 A g−1@‐20 °C. Furthermore, even at a temperature as low as −40 °C, the reversible capacity remains at 270 mAh g−1 at 0.06 A g−1. Extensive characterizations and theoretical calculations provide evidence that the optimized interface between the electrode and electrolyte effectively enhances the desolvation and migration of Na+ ions, particularly at low temperatures. In this work, Song et al. reported a surface‐modified hard carbon anode comprising atomic Co sites and rich curvature characteristics. Among them, the coated layer facilitates the formation of NaF‐rich SEI and the transportation kinetics of Na+ at the electrode/electrolyte interface. The synthesized optimal sample exhibits a superior low‐temperature performance of 270 mAh g−1 at −40 °C (equivalent to 83% capacity at 25 °C).