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Enabling Fast Na+ Transfer Kinetics in the Whole‐Voltage‐Region of Hard‐Carbon Anodes for Ultrahigh‐Rate Sodium Storage

Efficient electrode materials, that combine high power and high energy, are the crucial requisites of sodium‐ion batteries (SIBs), which have unwrapped new possibilities in the areas of grid‐scale energy storage. Hard carbons (HCs) are considered as the leading candidate anode materials for SIBs, however, the primary challenge of slow charge‐transfer kinetics at the low potential region (<0.1 V) remains unresolved till date, and the underlying structure–performance correlation is under debate. Herein, ultrafast sodium storage in the whole‐voltage‐region (0.01–2 V), with the Na+ diffusion coefficient enhanced by 2 orders of magnitude (≈10–7 cm2 s–1) through rationally deploying the physical parameters of HCs using a ZnO‐assisted bulk etching strategy is reported. It is unveiled that the Na+ adsorption energy (Ea) and diffusion barrier (Eb) are in a positive and negative linear relationship with the carbon p‐band center, respectively, and balance of Ea and Eb is critical in enhancing the charge‐storage kinetics. The charge‐storage mechanism in HCs is evidenced through comprehensive in(ex) situ techniques. The as prepared HCs microspheres deliver a record high rate performance of 107 mAh g–1 @ 50 A g–1 and unprecedented electrochemical performance at extremely low temperature (426 mAh g–1 @ −40 °C).