  The exponentially growing market of electrochemical energy storage devices
requires substitution of flammable, volatile, and toxic electrolytes. The use
of Water in salt solutions (WiSE) regarded as green electrolyte might be of
interest thanks to an association of key features such as high safety, low
cost, wide electrochemical stability, and high ionic conductivity. Here, we
report comprehensive chemical-physical study of circumneutral WiSE based on
ammonium acetate so as to investigate application in electrochemical energy
storage systems, with focus on the effect of pH, density, viscosity,
conductivity, and the ESW with salt concentration ranging from 1 to 30 mol/kg .
Data are reported and discussed with respect to the structure of the solutions
investigated by complemental IR and molecular dynamic study. The study is
addressed through the showcase of an asymmetric supercapacitor based on Argan
shell-derived carbon electrodes tested at temperatures ranging from -10 to 80
{\deg}C.
