Microstructure‐Dependent Charge/Discharge Behaviors of Hollow Carbon Spheres and its Implication for Sodium Storage Mechanism on Hard Carbon Anodes

Abstract Hard carbons are actively developed as a promising anode material for sodium ion batteries (SIBs). However, their sodium storage mechanism is poorly understood, leading to difficulties in design and development of high‐performance hard carbon anode materials. In this work, hollow carbon spheres (HCSs) with different shell thickness as a model material to investigate the correlation between the microstructural change and resulting Na + storage behavior during charge/discharge cycles are designed and synthesized. Ex situ X‐ray diffraction and Raman evidences reveal that an interlayer spacing change of the graphitic nanodomains occurs in HCS electrode, leading to a shift of the reversible capacity from the high‐potential sloping (HPS) region to the low‐potential plateau (LPP) region. This unusual capacity shift suggests a microstructure‐dependent Na + storage reaction on the HCS electrode and can be well explained by “adsorption‐intercalation” mechanism for these HCS materials. This work strengthens the understanding of the sodium storage behavior and provides a new perspective for the morphological and structural design of hard carbon anode materials for high‐performance SIBs.