Is the Solid Electrolyte Interphase Absent in Ether-Based Electrolytes for Sodium-Ion Batteries?

Solid electrolyte interphase (SEI), which is derived from electrolytes, plays a crucial role in determining the electrochemical performance of sodium-ion batteries (SIBs), however, the mechanisms by which electrolytes influence SEI formation remain unclear. This study focuses on the interface electrochemistry of electrolytes. By comparing typical ether-based and ester-based electrolytes, we find that no detectable SEI was observed in the ether-based electrolytes under the tested conditions, a conclusion verified by multiple characterization techniques. Theoretical calculations of molecular orbitals and solvent chemistry reveal that the electrochemical stability of ether-based electrolytes, attributed to the low reduction potential and high reaction energy barriers of ether solvent molecules, is the fundamental origin of the SEI absence. Our findings not only elucidate the superior kinetics of ether-based electrolytes in SIBs but also offer new perspectives on SIBs' interfacial electrochemistry, providing valuable guidance for future electrolyte design.