High-Energy Aqueous Sodium-Ion Batteries.

Abstract

Water-in-salt electrolytes (WISE) have largely widen the electrochemical stability window (ESW) of aqueous electrolytes by formation of passivating solid electrolyte interphase (SEI) on anode and also absorption of hydrophobic anion-rich double layer on cathode. However, the cathodic limiting potential of WISE is still too high for most high capacity anodes in aqueous sodium-ion batteries (ASIBs), and the cost of WISE is also too high for practical application. Herein, a low-cost 19 m (m: mol kg -1) bi-salts WISE with a wide ESW of 2.8 V was designed, where the low-cost 17 m NaClO4 extends the anodic limiting potential to 4.4 V, while the fluorine-containing salt (2 m NaOTF) extends the cathodic limiting potential to 1.6 V by forming a NaF-Na2O-NaOH SEI on anodes. The 19 m NaClO4 -NaOTF electrolyte enables a 1.75 V Na3V2(PO4)3||Na3V2(PO4)3\xa0 full cell to deliver an appreciable energy density of 70 W h kg -1 at 1 C with a capacity retention of 87.5 % after 100 cycles.