Polymer effect on lithium ion dynamics in gel polymer electrolytes: Cationic versus acrylate polymer

Abstract

In this work we study different ternary polymer gel electrolytes in order to analyze the influence of the type of polymer and its concentration on the lithium ion transport. Four ternary systems are prepared, containing either poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)-imide (PDADMATFSI) or poly(methyl methacrylate) (PMMA) as polymeric component, lithium bis(trifluoromethanesulfonyl)-imide (LiTFSI) as conducting salt, and either ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) imide (PYR14TFSI) or propylene carbonate (PC) as solvent. We study the lithium ion dynamics in dependence on polymer concentration for all systems. The samples are studied by 7Li and 19F Pulsed Field Gradient (PFG) nuclear magnetic resonance (NMR) diffusion experiments of the lithium ion as well as the TFSI− anion. The diffusion coefficients of the ions decrease strongly with increasing concentration of PMMA, but they decrease less significantly for increasing concentration of PDADMATFSI. Various comparisons of diffusion coefficient ratios highlight the role of the solvent and the polymer, respectively. Spin-lattice relaxation rates give an insight about the change in short range (local) dynamics of the lithium ion. In summary, the result show that PDADMATFSI acts as an efficient ionic cluster breaker between lithium and TFSI− and is thus a far better suitable polymer in electrolytes than PMMA.