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

Abstract 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 CoN 4 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.