Lithium-ion conductivity of the Nafion membrane swollen in organic solvents

The lithium-ion conductivity of the lithium form of the commercial perfluorinated membrane Nafion-115 was studied in a series of aprotic solvents in a wide temperature range. The highest ion conductivity was obtained for the sample kept in N,N-dimethyl formamide (DMF); its use in lithium-ion batteries, however, is restricted by its low electrochemical stability. Mixed solvents based on dimethyl sulfoxide (DMSO) with propylene carbonate (PC) and 1,2-dimethoxyethane (DME) additions were optimum solvents for ion transport. The Nafion membrane in the lithium form kept in a mixed solvent DMSO: PC: DME = 1: 1: 2 was characterized by high ion conductivity at room temperature (2.0 mS/cm) and the absence of phase transitions in the temperature range from–40 to +60°C. The activation energy of conductivity of the samples kept in DMF, DMSO, and mixed solvents based on DMSO above the transition temperature was 15–20 kJ/mol.