Ion transport effects in a solid polymer electrolyte due to salt substitution and addition using an ionic liquid.

We investigated mass and charge transport in amorphous salt-in-poly(ethylene oxide) (PEO) electrolytes with NaI and/or the ionic liquid (IL) EMImTFSI (1-ethyl-3-methylimizadolium bis(trifluoromethylsulfonyl)imide) as salt component. Combining the results of ion conductivity, pulsed field gradient nuclear magnetic resonance, and radiotracer diffusion measurements, it is found that over wide temperature ranges both the cation and anion diffusion coefficients and the charge diffusivity are distinctly larger in PEO(20)EMImTFSI than in PEO(20)NaI complexes, where the monomer-to-salt mole ratio equals 20. In the mixed-salt complexes PEO(20)NaI(1)EMImTFSI(1) and PEO(20)NaI(0.5)EMImTFSI(0.5), we observe a slowing down of the IL ions EMIm and TFSI along with a diffusivity enhancement of the I anion compared to the single-salt base complexes. For the cation Na, a diffusivity increase is only effected by IL substitution, but because of the concomitant decrease of the Na concentration, it does not predict more effective charge transfer in a battery cell configuration.