Fluoride ion batteries offer advantages over currently used lithium ion batteries due to fluorine's high electronegativity and potentially high energy density, but a suitable electrolyte must be chosen to serve as a fluoride ion shuttle. Conventional polymer electrolytes have several problems including build-up of counter-ions, solvent leaking, and low transference numbers. As an alternative to conventional polymer electrolytes, a single ion conducting polymer, or ionomer, was designed. The ionomer consists of a polysiloxane backbone with poly(ethylene glycol) and tetrabutyl phosphonium side chains and a freely diffusing bromide or fluoride anion. In this system, the phosphonium cation is covalently bound to the polymer matrix and does not contribute to the conductivity, producing an anion transference number approaching unity. The restriction of cation motion and removal of organic solvent eliminate the complications that arise from the buildup of cations at the electrodes and leaking of the organic solvent. These ionomers have very low glass transition temperatures (between -70 and -80�C, due to the flexible nature of the polysiloxane backbone) that increase weakly with ion content and are independent of anion type. Spin lattice relaxation rates (1/T1) for 19F and 31P nuclei in polysiloxane-based ionomers of varying ion content were investigated using nuclear magnetic resonance spectroscopy. The resulting dynamics, including activation energies for motion, are compared to results from conductivity measurements using dielectric relaxation spectroscopy.

Solid state NMR investigation of ion motion in polysiloxane-based ionomers

248th National Meeting (2014)

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