Water in Salt electrolytes are new promising materials for application in lithium batteries, which comprise aqueous solutions of super-concentrated lithium salts (concentration >3M) with some interesting properties such as high electrochemical stability window, high lithium transference number, good ionic conductivity and decoupling of ionic mobility from viscosity. Experiments performed in the Helmholtz Zentrum-Berlin show that these solutions present nano-heterogeneities of around 1.25nm evidenced by a broad peak in SANS curves. In a battery, the electrolyte is confined inside the pores of the carbon electrode, which means that the properties may be different from the ones in the bulk solution. The objective of this proposal is to shed some light on the structure of these electrolytes when confined in mesoporous carbon, in order to better understand processes inside a battery system.