Electrolyte solvation structure manipulation enables safe and stable aqueous sodium ion batteries†
Aqueous sodium ion batteries (ASIBs) have been limited by their poor electrochemical stability. The use of highly concentrated aqueous electrolytes is considered as an efficient strategy that increases the voltage window and improves the cycling stability. However, their cost and safety are still subjects of serious concern for practical applications. In this work, we show that a new multi-component aqueous electrolyte (MCAE) could widen the voltage window to 2.8 V with the formation of a composite solvent sheath and promote the generation of a uniform solid electrolyte interface (SEI) layer consisting of complexes with inorganic salt Na2CO3 and other organic components, which significantly inhibits the side reaction. Thus, this MCAE guaranteed good electrochemical stability of Na3V2(PO4)3 and NaTi2(PO4)3, which suffer from severe performance degradation in aqueous electrolytes. Simultaneously, this MCAE exhibits high safety, a wide operating temperature range (−50 °C to 50 °C) and high ionic conductivity because of urea and N,N-dimethylformamide (DMF) additives. In addition, a nickel-based Prussian blue analog (NiHCF)/NaTi2(PO4)3 sodium-ion full battery using such a MCAE delivers 80% capacity retention after 2000 cycles at 2C rate. Moreover, our work provides important guidelines to investigate safe, environmentally friendly and high-stability ASIBs for large-scale energy storage.