Effect of Vapor Carbon Coating on the Surface Structure and Sodium Storage Performance of Hard Carbon Spheres

Hard carbons have received considerable attention as anode materials for sodium‐ion batteries (SIBs). However, it is still a challenge to improve the plateau capacity and initial coulombic efficiency (ICE) of hard carbons. Herein, a facile vapor carbon‐coating method is used to modify the surface structure of carbon spheres (CS) via the pyrolysis of polypropylene (PP), aiming to seal the exposed pores through a high‐quality carbon layer. CS@2%PP exhibits highly improved sodium storage performance compared to that of the pristine CS, which delivers a plateau capacity of 220 m Ah g −1 and an ICE of 81%. Further investigations show that the improved sodium storage performance of CS@2%PP can be mainly attributed to the reduced structural defects on the surface, lower specific surface area (11.5 m 2 g −1 ), and increased closed pores (12.5%) via carbon coating. The results prove that the surface vapor carbon coating is a facile route to improve the plateau capacity and ICE of hard carbon anodes in SIBs.