Elucidating the Mechanism of Fast Na Storage Kinetics in Ether Electrolytes for Hard Carbon Anodes

The sodium storage performance of a hard carbon (HC) anode in ether electrolytes exhibits a higher initial Coulombic efficiency (ICE) and better rate performance compared to conventional ester electrolytes. However, the mechanism behind faster Na storage kinetics for HC in ether electrolytes remains unclear. Herein, a unique solvated Na+ and Na+ co-intercalation mechanism in ether electrolytes is reported using designed monodispersed HC nanospheres. In addition, a thin solid electrolyte interphase film with a high inorganic proportion formed in an ether electrolyte is visualized by cryo transmission electron microscopy and depth-profiling X-ray photoelectron spectroscopy, which facilitates Na+ transportation, and results in a high ICE. Furthermore, the fast solvated Na+ diffusion kinetics in ether electrolytes are also revealed via molecular dynamics simulation. Owing to the contribution of the ether electrolytes, an excellent rate performance (214 mAh g(-1) at 10 A g(-1) with an ultrahigh plateau capacity of 120 mAh g(-1)) and a high ICE (84.93% at 1 A g(-1)) are observed in a half cell; in a full cell, an attractive specific capacity of 110.3 mAh g(-1) is achieved after 1000 cycles at 1 A g(-1).

Automated summary

The sodium storage performance of hard carbon in ether electrolytes is superior, attributed to a unique solvated Na+ and Na+ co-intercalation mechanism in designed monodispersed HC nanospheres. Additionally, a thin solid electrolyte interphase film formed in ether electrolytes facilitates Na+ transportation and results in a high initial Coulombic efficiency.