Simultaneously enabling superior ICE and high rate/cycling stability with a hollow carbon nanosphere anode for sodium-ion storage

Abstract

Despite tremendous endeavors to tackle the low initial coulombic efficiency (ICE) of hard carbons by reducing the intrinsic defects and porous nanostructure, an ongoing obstacle is the trade-off between the ICE and rate/cycling stability originated from the distinct microstructure-related charge storage process, greatly hindering practical deployment of sodium-ion batteries. Herein, we propose the elaborate manipulation of the microstructure of hollow carbon nanospheres (HCNs) to surmount the above paradox, thus simultaneously achieving high ICE and rate/cycling stability. By increasing the carbonization temperature, gradual ordering of pseudo-graphitic nanodomains with decreased defects and enriched closed pores is observed, contributing to the elevated ICE and large plateau capacity; whereas the rate and cycling stability are gradually deteriorated, mainly due to the dominance of diffusion-limited intercalation and pore filling with sluggish kinetics and large volume variation. Therefore, the optimized HCN with a suitable carbonization temperature of 1300 °C exhibits ICE up to 84% while maintaining remarkable cycling stability up to 10 000 cycles and excellent rate capacity (175 mA h g⁻¹ at 2 A g⁻¹). The ICE is significantly higher than the majority of reported HCNs and the combination of superior ICE and cycle life is still at a record value among hard carbon materials. This work will offer new inspiration for the rational engineering of carbon anode materials with holistic performance optimization towards realistic applications.