Anion-derived cathode interface engineering enables ether-based electrolytes for sodium-ion batteries

High-performance sodium-ion batteries (SIBs) require not only non-aqueous electrolytes with high ion conductivity but also high interfacial compatibility with both electrodes. Ether-based electrolytes are considered one of the most promising electrolyte systems for SIBs due to the advantages of high reduction stability and weakly desolvating power. However, conventional ether-based electrolytes are easy to decompose and deteriorate on the cathode/electrolyte interface under high voltage, which greatly restricts their practical application in SIBs. Herein, a novel and effective interfacial stabilization strategy is proposed and systemically investigated. A homogeneous and compact cathode electrolyte interphase (CEI) film rich in fluorides and borides can be successfully constructed on the cathode surface by pre-cycling of NVP@C cathode in the NaODFB-DEGDME electrolyte. The ODFB anion-derived CEI film can effectively inhibit the continuous oxidation decomposition of NaPF6-DEGDME electrolytes. As a result, the Na||NVP@C half-cell can stably cycle for 1500 cycles with high average Coulombic efficiency (CE, >99.7 %) at 5C. This work illustrates the significance of the composition and structure of CEI film for improving the interfacial stability of high-voltage SIBs with ether-based electrolytes.