Fluorine-Free Water-in-Salt Electrolyte for Green and Low-Cost Aqueous Sodium-Ion Batteries

The highly concentrated water-in-salt electrolyte (WiSE) containing sodium acetate and potassium acetate demonstrates surprising performance (specific capacity of 37 mA h(-1) g(-1) at the 5th cycle and average discharge voltage of 0.82 V) in aqueous sodium-ion batteries (SIBs) based on Na2MnFe(CN)(6) and NaTi2(PO4)(3). The fluorine-free electrolyte offers a wide electrochemical stability window and compatibility with Al current collector. The electrolyte, current collector, and the electrode materials based on abundant elements make the proposed battery chemistry safe, low-cost, and environmentally friendly.