Synthesis and Application of an Aromatic Sulfonate Sodium Salt for Aqueous Sodium‐Ion Battery Electrolytes

Abstract

The two‐step synthesis of sodium (2,3,5,6‐tetrafluorophenoxy) diethane sulfonate (Na‐TFP) is reported, starting from 2,3,5,6‐tetrafluorohydroquinone as the precursor. Compared with conventional aqueous electrolytes such as 0.5 m NaClO4 and Na2SO4, the 0.5 m aqueous solution of Na‐TFP provides higher ionic conductivity over a wide range of temperature (e.g., >60 mS cm−1 at 20 °C and >70 mS cm−1 at 30 °C) and a wider electrochemical stability window. Electrochemical cells with Na2VTi(PO4)3 as the positive electrode active material and a carbon‐based negative electrode provide a stable capacity for more than 450 cycles in 0.5 m Na‐TFP. Additionally, symmetric cells with Na2VTi(PO4)3 as the active material for the negative and positive electrode are studied. The cells employing 0.5 m Na‐TFP exhibit a good cycling stability at a high dis‐/charge rate of 5C for more than 50 cycles, which is superior to the performance of the cells employing 0.5 m aqueous solutions of NaClO4 and Na2SO4 as the electrolyte. The design of this bifunctional salt may trigger new ideas for the development of water‐based sodium‐ion battery electrolytes.

Optimization Strategies Toward Functional Sodium‐Ion Batteries

“…This system provided better cyclic stability of 400 cycles at 2 C with a capacity retention of 90%. [80] To address the flammability issue of non-aqueous electrolytes, Colbin et al reported a fluorine-free and flame-retardant non-aqueous electrolyte using 0.38 M sodium bis(oxalato)borate (NaBOB) in triethyl phosphate (TEP) and also provided satisfactory passivation of hard carbon at low salt concentration and without the use of any additives. This electrolyte exhibited ionic conductivity of 5 mS cm −1 at room temperature and a viscosity of 2.674 mPaÁs.…”