Mixed-anion effect in polyethylene-oxide-based sodium-ion-conducting polymer electrolytes

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Abstract
Electrical conductivity, mobility, cationic and anionic transference numbers and numbers of respective mobile charge carriers have been measured for polyethylene-oxide-based polymer electrolytes complexed with mixed anion salts. The systems studied are (polyethylene oxide)15: ((1-x)NaI+xNaSCN) and (polyethylene oxide)15: ((1-x)NaI+xNaClO4). It is shown that the presence of mixed anions in the polymer salt complex electrolytes changes the relative number of mobile cations and anions together with their respective transference numbers as well as the crystallinity of the polymer matrix. A qualitative correlation has been established between the crystallinity, tcation, conductivity and the number of mobile anions/cations. The maximum change in the cationic (Na+) transference number was for polyethylene oxide: NaI for which tNa+ could be increased from 0.18 to about 0.6 in the mixed anion system (polyethylene oxide)15: (0.35NaI+0.65NaSCN) with comparable conductivity.