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 (approximate to 10(-7) cm(2) 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 (E-a) and diffusion barrier (E-b) are in a positive and negative linear relationship with the carbon p-band center, respectively, and balance of E-a and E-b 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 degrees C).

Automated summary

This study reports an ultrafast sodium storage throughout the whole-voltage region by rationally adjusting the physical parameters of hard carbons through a ZnO-assisted etching strategy. It is found that the storage capacity of sodium is related to the p-band center of the carbon material, and the balance between adsorption energy and diffusion barrier is critical in improving charge-storage kinetics. The prepared hard carbon microspheres exhibit high rate performance and unprecedented electrochemical performance at extremely low temperature.