Water/DMSO-Based Hybrid Electrolyte and Urea Additive Engineering for Performance Regulation in Aqueous Sodium Batteries

Electrochemical energy storage devices are of interest, especially aqueous sodium ion batteries (ASIBs), due to their safety, low-cost, and environmental friendliness. However, ASIBs suffer from poor cyclic stability and a narrow electrochemical window, which hinders their large-scale application. Compared to the traditional dilute saline electrolytes, high concentration electrolytes show a wider potential window. In this study, we designed a novel NaClO 4 -H 2 O/DMSO-Urea hybrid electrolyte to suppress these problems, in which DMSO and Urea create a synergistic effect. The formation of hydrogen bonds between DMSO and H 2 O reduced water activity, thereby suppressing the hydrogen evolution reaction. The addition of DMSO resulted in the reduction from −1.2 to −1.6 V for the hydrogen evolution potential. Therefore, we were able to expand the electrochemical window on the basis of reducing the concentration of sodium salts. Moreover, the addition of Urea facilitated formation of a stable solid electrolyte interface on the electrode surface, which improved the cycling stability of NVP/C (Na 3 V 2 (PO 3 ) 4 /C) symmetric cell which exhibited a specific capacity of 59.7 mAh g −1 with the retention capacity of 80.1% after 200 cycles at 1 C. This work points out a promising strategy for developing stable and wide voltage aqueous electrolyte.