  One challenge in developing the next generation of lithium-ion batteries is
the replacement of organic electrolytes, which are flammable and most often
contain toxic and thermally unstable lithium salts, with safer, environmentally
friendly alternatives. Recently developed Water-in-Salt Electrolytes (WiSEs)
were found to be a promising alternative, having also enhanced electrochemical
stability. In this work, we develop a simple modified Poisson-Fermi theory,
which demonstrates the fine interplay between electrosorption, solvation, and
ion correlations. The phenomenological parameters are extracted from molecular
simulations, also performed here. The theory reproduces the electrical double
layer structure of WiSEs with remarkable accuracy.
