THE EFFECT OF COSOLVENTS AND ADDITIVES ON THE ELECTROCHEMICAL PROPERTIES OF [(ME)3PHN][AL2CL7] MELTS

The small Gutmann donor number solvents 1,2-dichlorobenzene, anisole and diphenylether were evaluated as cosolvents of trimethyl-phenyl-ammonium chloride/aluminium chloride melts in view of a potential use of these systems in batteries. The amalgamated aluminum electrode was introduced, in order to enhance the reliability of diffusion coefficient measurements and kinetic parameter evaluations. This technique allowed the determination of diffusion coefficients by CV on a stationary electrode, while overall kinetic parameters were derived from Tafel plots obtained by rotating disc linear sweep voltammetry. With anisole as a cosolvent, aluminum deposition was faster on a pure aluminum electrode than on amalgamated aluminum, as evidenced by the corresponding Tafel constants. Diphenylether can be used as a cosolvent together with 1,2-dichlorobenzene, but such solutions show marked passivation in the cathodic region. Anisole is a good solvent for AlCl3 but the solutions have very low conductivity. Insight into the speciation of pure and diluted melts was provided by peak-shape analysis of Al-27 NMR spectra.