A Divalent Lithium Salt Li2B12F12 Dissolved in Propylene Carbonate Studied by NMR Methods

Abstract

A divalent lithium salt dissolved in propylene carbonate (PC) with four different concentrations was studied by NMR methods and ionic conductivity. The individual diffusion coefficients were measured by , , and pulsed-gradient spin-echo NMR for the solvent PC , lithium , and anion . Because two-step salt dissociation processes can be assumed for the divalent , the existence of in addition to and must be taken into account. The comparison was made with the diffusion coefficients of in PC. The plots of ion diffusion coefficients vs solvent diffusion coefficient were linear for both and PC in solutions. Although the diffusion is much faster than lithium diffusion for the in PC, the and of the have similar values in the temperature range measured for the four different salt concentrations. The experimental parameters and calculated from the individual diffusion coefficients suggest that the PC solvation around can be assumed in addition to the PC solvation around Li. Tentatively, the Nernst–Einstein ionic conductivities were calculated from the and under the assumption of the complete ion dissociation. The temperature- and concentration-dependent behaviors resemble those of the ionic conductivity observed by the electrochemical ac method.