Nuclear magnetic resonance study of PEO-chitosan based polymer electrolytes

This work investigates lithium dynamics in a series of polymer electrolytes formed by poly(ethylene oxide) PEO, chitosan (QO), amino propil siloxane (pAPS) and lithium perchlorate by means of nuclear magnetic resonance techniques. Lithium (⁷Li) lineshapes and spin-lattice relaxation times were measured as a function of temperature. The results suggest that the chemical functionality of QO, particularly the amine group, participate in coordinating lithium ion in the composites. The competition between QO and PEO for lithium ions is evident in the binary system. In the ternary electrolyte containing PEO, QO and pAPS, it is observed that the lithium ions can competively interact with the two polymers. The heterogeneity, at a local microscopic scale, is revealed by a temperature-dependent equilibrium of lithium ion concentration between at least two different microphases; one dominated by the interactions with chitosan and the other one with polyether. The data of the ternary electrolyte was analysed by assuming two lithium dynamics, the first one associated to the motion of the lithium ion dissolved in PEO and the second one associated to those complexed by the chitosan.