Impedance and polarisation studies of new lithium polyelectrolyte gels

Electrical conductivity, interaction with lithium metal and apparent Li+ transference number of gel polyelectrolytes was examined by the impedance spectroscopy and the dc polarisation of cells. Gel polyelectrolytes were obtained by crosslinking of plasticized lithium salts derived from comb-like half ester of maleic acid copolymer. Two gels contained additives: either BF3 as an agent complexing carboxylic anions or LiN(CF3SO2)2 salt as a source of additional lithium ions. The measured impedance spectra of cells Li/gel/Li were simulated by an equivalent circuit. The time evolution of the circuit parameters indicated growth of passivation layer and degradation of the electrolyte. In all studied gels, the apparent Li+ transference number had low values, which decreased upon time of storage of cells with lithium electrodes. Probably small ions are formed upon chemical interaction between lithium and dimethoxyethylenesulfoxide—the polar solvent used as a plasticizer.