A Low-Concentrated Electrolyte with a 3.5 V Electrochemical\nStability Window, Made by Restructuring the H‑Bond Network,\nfor High-Energy and Long-Life Aqueous Sodium-Ion Batteries

The\nnarrow electrochemical stability window (ESW) of electrolytes\nis primarily responsible for the low energy density and poor cycle\nlife of aqueous sodium-ion batteries (ASIBs). Although water-in-salt\nelectrolytes can effectively widen the ESW, their high salt concentration\nleads to high costs. In this work, we found that weak-polar solvents\nhave more advantages in broadening the ESW than strong-polar solvents.\nTaking 1,3,6-hexane­tricarbonitrile as an example, it evidently\nenhances the stability of water by weakening the hydrogen bond network.\nConsequently, it broadens the ESW to 3.5 V at a relatively low concentration\nand enables Na<sub>2</sub>FeFe(CN)<sub>6</sub>||​NaTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> full cells with a capacity retention\nof 70% after 10 000 cycles and an energy density of 71 Wh kg<sup>–1</sup>, based on the active materials’ mass of both\nelectrodes. This work offers new prospects for the development of\nhigh-energy and long-life aqueous sodium-ion batteries for large-scale\nenergy storage.