An investigation of anionic conductivity of the composite polymer electrolyte based on PEO and Pr4N+I- salt with the filler TiO2

Abstract

Polymer Electrolytes (PEs) have been studied to use in many devices such as lithium rechargeable batteries, fuel cells, electrochromic devices, etc. Most of the previous research work has been carried out to study the cation conductivity of PEs and their conductivity enhancement with the addition of various fillers. There are not many reports on studying the effect of filler on anionic conductivity in PEs. In this study, the anion conductivity was investigated using the anion conducting PE with tetrapropylammonium iodide (Pr4N+I-) as the salt, polyethylene oxide (PEO) as the polymer and titanium dioxide (TiO2) as the filler.
The solvent casting method was used to prepare PE samples, (PEO)mPr4N+I- (m = 5, 10, 20, 30, 40, 50, 60, 80 and 90), where m:1 is the O:I (oxygen:iodine) ratio of the samples. The solvent casting method yielded visually homogeneous composite PE films with average thickness of 100 – 400 μm. Estimated conductivities of the filler free samples were in the order of 10-9 S cm-1 at room temperature and relatively high anionic conductivity was observed for the samples (PEO)60Pr4N+I- and (PEO)50Pr4N+I-. The filler was added as a weight percent (5%, 10%, 15%, 20% and 30%) to the 60:1 and 50:1 samples. The thermal studies were carried out to investigate the melting enthalpies of the filler free and filler added samples using the Pyris 1 differential scanning calorimeter (DSC). 
Unlike the cation conducting PEs, here the anionic conductivity did not increase with the addition of the filler. However according to the conductivity and DSC results it can be concluded that the amorphous nature of the samples was increased. Optical micrographs confirmed this nature showing a reduction in size of the spherulites with addition of the filler.