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 .