Self-diffusion coefficients of lithium, anion, polymer, and solvent in polymer gel electrolytes measured using 7Li, 19F, and 1H pulsed-gradient spin-echo NMR

Abstract

Four series of solution and corresponding polymer gel electrolyte systems were studied. The systems were composed of a solvent (γ-butyrolactone (GBL) or propylene carbonate (PC)), (three different concentrations of) a lithium salt (LiBF 4 or lithium bis(trifluromethanesulfonyl)-imide (LiTFSI, LiN(SO 2CF 3) 2)), and poly(ethylene glycol diacrylate) of molecular weight 4000 (PEO), which was cross-linked to form the polymer gels. The self-diffusion coefficients of the lithium, the anions, the solvents and the polymer were obtained independently using 7Li, 19F and 1H pulsed-gradient spin-echo NMR measurements. From the individual diffusion coefficients of each component of the GBL–LiBF 4, GBL–LiTFSI, PC–LiBF 4, and PC–LiTFSI solutions and the corresponding polymer gel electrolytes, the solvation and the solvent-dependent behaviour of the lithium and the anions are clearly shown. Especially in the gels, the lithium binding with the PEO matrix were found to be quite different depending on whether the solvent was PC or GBL.