The first lithium zeolitic inorganic-organic polymer electrolyte based on PEG600, Li2PdCl4 and Li3Fe(CN)6: part II, thermal stability, morphology and ion conduction mechanism

This paper reports studies on the morphology, thermal stability, NMR and electrical spectroscopy of the first lithium zeolitic inorganic-organic polymer electrolyte (Z-IOPE) with the formula [FexPdy(CN)zClv(C2nH4n+2On+1)Lil]. Both 1H and 7Li NMR linewidth, spin-lattice relaxation, and pulsed field gradient diffusion measurements were conducted, and the results suggest that the lithium ion transport is correlated with polymer mobility, as in the case of 'conventional' polymer electrolytes. A detailed study of the mechanism of ion conduction in bulk material has been carried out also by electrical spectroscopy measurements in the 10 mHz-1 GHz range. The electrical spectra for frequencies higher than 15 kHz evidenced the presence of relaxation events associated to local ion motion dynamics and long range diffusion. These two phenomena were interpreted in terms of (a) ion hopping processes; (b) site relaxations; and (c) host medium reorganization processes. Taken together, these studies demonstrated that at temperatures higher than 35 deg. C, the Z-IOPE conducts ionically by charge transfer mechanisms mainly regulated by ion hopping between equivalent polyether coordination sites followed by correlated host medium reorganizations. Finally, a conductivity of 5.3x10-5 S cm-1 at 35 deg. C classifies this hybrid inorganic-organic network as a good lithium ion conductor