Enhanced Anion‐Derived Inorganic‐Dominated Solid Electrolyte Interphases for High‐Rate and Stable Sodium Storage

Abstract

It is highly desirable for the promising sodium storage possessing high rate and long stable capability, which are mainly hindered by the unstable yet conventional solvent‐derived organic‐rich solid electrolyte interphases. Herein, an electrolyte solvation chemistry is elaborately manipulated to produce an enhanced anion‐derived and inorganic components‐dominated solid electrolyte interphases by introducing a low permittivity (4.33) bis(2,2,2‐trifluoroethyl) ether diluent into the sodium bis(trifluoromethylsulfonyl)imide‐dimethoxyethane‐based high concentration electrolyte to obtain a localized high concentration electrolyte. The bis(2,2,2‐trifluoroethyl) ether breaks the balance of original cation solvation structure and tends to interact with Na+‐coordinated dimethoxyethane solvent rather than Na+ in high concentration electrolyte, leaving an enhanced Coulombic interaction between Na+ and (FSO2)2N−, and more (FSO2)2N− can enter the Na+ solvation shell, forming a further increased number of Na+‐(FSO2)2N−‐dimethoxyethane clusters (from 82.0% for high concentration electrolyte to 94.3% for localized high concentration electrolyte) at a low salt dosage. The preferential reduction of this (FSO2)2N−‐enriched clusters rather than the dimethoxyethane‐dominated Na+ solvation structure produces an enhanced anion‐derived and inorganic components‐dominated solid electrolyte interphases. The reversible charge storage process of Na is decoupled by operando Raman along with a shift of D and G peaks. Benefiting from the enhanced anion‐derived electrode‐electrolyte interface, the commercial hard carbon anode in localized high concentration electrolyte shows a well rate capability (5 A g−1, 70 mAh g−1), cycle performance and stability (85% of initial capacity after 700 cycles) in comparison to that of high concentration electrolyte (68%) and low concentration electrolyte (only 5% after 400 cycles), indicative of uniqueness and superiorities towards stable Na storage.