Solvation structure and solid electrolyte interface engineering for excellent Na+ storage performances of hard carbon with the ether-based electrolytes

Compared with the commonly used ester-based electrolytes, more excellent Na+ storage performances can be achieved for hard carbon in the ether-based electrolyte. Whereas, the mysteries underlying such excellent electrochemical performances are still unclear. Herein, the impressive Na+ storage behaviors of hard carbon in the ether-based electrolyte were clarified based on a profound insight of Na+ storage mechanism. It’s revealed that the co-intercalation behavior is responsible for the lower de-solvation energy, which contributes to a facile de-solvation process and the enhanced charge transfer kinetic. Besides, a thin, amorphous and flexible solid-electrolyte interface (SEI) in ether-based electrolyte with a specific structure where the amorphous nanoparticles are coated with organic species was probed. And the resulted SEI is beneficial to achieving much lower activation energy for Na+ diffusion through SEI and a stable interface during cycling due to its excellent ion-conducting ability and mechanical flexibility. It’s also demonstrated that ether-based solvent with short chain length plays a positively impact on the Na+ storages, which also well agrees with the above synergistic effect. The research plays a significant role in elucidating the uniqueness of ether-based electrolytes to hard carbon and promoting its practical application in future sodium-based battery chemistries.