Influence of Li-Salt Concentration on Redox Potential of Lithium Metal and Electrochemistry of Ferrocene in DMSO-Based Electrolytes

High concentrated liquid aprotic electrolytes have been proposed as a new class of electrolytes and received intense attention for use in Li-ion and Li-metal batteries. We investigate the effect of the Li-salt concentration (up to 3M) in the supporting electrolyte on the redox potential of lithium metal in Dimethyl Sulfoxide (DMSO)-based electrolytes. Measuring the electromotive force (emf) of concentration cells allowed to experimentally assess the change of the Li/Li+ potential as function of the salt concentration in the electrolyte. In the low salt concentration region, a linear change of the Li/Li+ potential is observed whereas at higher salt concentrations it rises exponentially. Experimental findings are elucidated using two forms of the Nernst equation and remarkable agreement is obtained, thus allowing for theoretical prediction of the change in the alkali metal redox potential. The shift of the Li potential is found to be greatly influenced by the concentration and availability of uncoordinated solvent, which can be estimated from Raman analysis. Finally, the effect of the Li-salt concentration on the diffusion coefficient (D) and heterogeneous rate transfer kinetics (k0) of Ferrocene (Fc) is investigated by rotating disk electrode (RDE) and cyclic voltammetry in the same electrolytes.