Suppression of Interphase Dissolution via Solvent Molecule Tuning for Sodium Metal Batteries.

Solvent molecule tuning is used to alter redox potentials of solvents or ion-solvent binding energy for high-voltage or low-temperature electrolyte. Herein, we propose an electrolyte design strategy that effectively suppresses solid electrolyte interphase (SEI) dissolution and passivates highly-reactive metallic Na anode via solvent molecule tuning. With rationally lengthened phosphate backbones with -CH 2 - units, the low-solvation tris(2-ethylhexyl) phosphate (TOP) molecule effectively weakens the solvation ability of carbonate-based electrolytes, reduces the free solvent ratio and enables an anion-enriched primary Na + ion solvation sheath. The decreased free solvent and compact lower-solubility interphase established in this electrolyte prevent electrodes from the continuous SEI dissolution and parasitic reactions at both room temperature (RT) and high temperature (HT). As a result, the Na/Na 3 V 2 (PO 4 ) 3 cell with the new electrolyte achieves impressive cycling stability of 95.7% capacity retention after 1800 cycles at 25 °C, and 62.1% capacity retention after 700 cycles at 60 °C. Moreover, TOP molecule not only maintains the nonflammable feature of phosphate but also attains a higher thermal stability, which endows the electrolyte with high safety and thermal stability. Our design concept for electrolytes offers a promising path to long-cycling and high safe sodium metal batteries. This article is protected by copyright. All rights reserved.