To minimize the ecological implications associated with battery use, we need to choose chemistries with a minimum footprint on nature. This is why efforts are currently being made on aqueous electrolytes, with the aim of enlarging the electrochemical window of water, which is only 1.23 V, to provide a cheaper, safer and non-toxic alternative to organic electrolytes. This desire was actually realized through the use of salt-concentrated aqueous electrolytes (24 M Li-TFSI), known as WiSE (Water in Salt Electrolyte), which can operate at potentials in excess of 3 V.
This lecture has attempted to put these new electrolytes(e.g. a mixture in which the solute outweighs the solvent in terms of weight and volume) into perspective. A quick review of the literature showed us that this concept is not new, having been introduced by A. Angel in 1993 as "Polymer in salt", with the subsequent observation of beneficial effects in terms of improved cathodic and anodic stability of non-aqueous electrolytes with a high salt content.
Subsequently, the science behind this phenomenon, which lies in the modification of the inner Helmholtz layer both in nature and composition, was described. Thus, during reduction, TFSI- anions migrate preferentially to the interface where they decompose, leading to the formation of an insoluble LiF layer, thus postponing water reduction to a lower potential.
