Disordered turbostratic nanodomain-dominated hard carbon for fast and ultra-stable sodium ion storage

The relationship between the microstructure of hard carbon (HC) and the sodium storage mechanism is crucial for the development of high-performance HC. Herein, nitrogen-oxygen co-doped carbon nanotubes (NOCN) were successfully synthesized through low-temperature carbonization, demonstrating pronounced "slope-dominated" features. Therefore, NOCN-600 exhibits excellent rate performance (150 mAh g(-1) at 20 A g(-1)) and stability (70.6 % after 9000 cycles). Further mechanistic insights revealed that the storage behavior of Na+ can be classified into three stages: adsorption (>0.4 V), pseudo-adsorption (0.4-0.1 V), insertion (<0.1 V). Interestingly, Na(+ )insertion was found to coincide with pseudo-adsorption due to an uneven structure of pseudo-graphite layers in HC. Abundant defects and a larger specific surface area are beneficial for ion adsorption, while wider interlayer spacing as well as smaller pseudo-graphitic domains are conducive to ion intercalation. This work will provide insight into sodium storage mechanisms and guide future developments of high-performance HC materials.