Precise Control of the Graphitic Microcrystal Morphology and Pore Structure in Carbon Nanocoils for Highly‐Efficient Sodium Storage

Abstract Hard carbon (HC) stands as one of the most promising anode materials for sodium‐ion batteries (SIBs), yet constructing HC with tailored microstructures to achieve superior electrochemical performance remains challenging. Herein, a novel high‐capacity HC material has been synthesized by leveraging the amorphous‐polycrystalline characteristics of carbon nanocoils (CNCs) through sequential pore engineering: pore creation, pore filling, and pore structure regulation. Specifically, KOH etching first creates abundant open pores, followed by CVD (Chemical Vapor Deposition) processing to grow graphitic microcrystals within their micropores. Subsequent high temperature thermal treatment regulates the morphology of graphite microcrystals enriching the closed pores. By varying the CVD duration, the size of graphitic microcrystals and the pore structure in the synthesized HC could be conveniently tailored. It is found that when the carbon microcrystals have the relatively optimal structural parameters, the electrode exhibited an exceptional sodium storage capacity of 398.6 mAh g ⁻¹ at 25 mA g ⁻¹ , along with outstanding cycling stability. Furthermore, the direct observation of microstructural evolution in HC during the charge‐discharge process reveals a sequential sodium storage mechanism of adsorption, intercalation of sodium ions, and especially the sodium clusters formation in micropores on the voltage plateau region below 0.1 V. This study provides a feasible strategy for designing high‐performance SIBs.