Conductivity enhancement in K+-ion conducting dry Solid Polymer Electrolyte (SPE): [PEO: KNO3]: A consequence of KI dispersal and nano-ionic effect

Flexible films of dry Solid Polymer Electrolytes (SPEs): [PEO: KNO3] in varying salt concentrations have been hot-press cast. Salt concentration dependent conductivity study revealed two SPE films: [95PEO: 5KNO(3)] and [70PEO: 30KNO(3)] exhibiting relatively higher room temperature conductivity (sigma(rt)) similar to 2.76 x 10(-7) S/cm and similar to 4.31 x 10(-7) S/cm respectively. In order to increase sigma(rt) further, two strategies have been adopted. Firstly, fractional amount of KI has been dispersed as IInd-phase active filler into above two SPE film compositions which acted as Ist-phase host and Composite Polymer Electrolyte (CPE) films were hot-press cast. Filler particle concentration dependent conductivity study identified CPE films: [(95PEO: 5KNO(3)) + 7KI] and [(70PEO: 30KNO(3)) + 10 KI] as optimum conducting films with sigma(rt) similar to 6.15 x 10(-6) S/cm and similar to 3.98 x 10(-6) S/cm respectively. sigma(rt)-enhancement of approximately an order of magnitude was achieved by this approach. In second approach, dry powder mixture of (KNO3 + KI), in ratio that of above two CPE films, were subjected to high energy ball-milling separately for different durations prior to casting the films again. The conductivity measurements as a function of milling time identified CPE films: [(95PEO: 5KNO(3)) + 7KI] and [(70PEO: 3OKNO(3)) + 10 KI] in which two respective (KNO3 + KI) ratios milled for 4- and 6-h, exhibited almost similar value of sigma(rt) similar to 2.09 x 10(-5) S/cm. This approach increased sigma(rt) further by similar to 3-6 fold. The reason attributed for this has been Nano-ionic effect introduced at the interphase boundaries between KNO3 and KI, as a consequence of milling. These films have been referred to as milled CPE films. Subsequently, all the optimum conducting SPE and CPE (unmilled/milled) films were subjected to various characterization studies in order to evaluate their utility in potential All-Solid-State batteries. Ion transport behaviour has been characterized in terms of ionic conductivity (sigma), total ionic (t(ion)) and cation (t(+)) transference numbers, evaluated using different ac/dc techniques. Temperature dependent conductivity measurements have also been done to compute activation energy (E-a) value by linear least square fitting of respective 'log sigma -1/T' plots. Materials characterization vis-a-vis complexation of salt in polymeric host has been confirmed by SEM/XRD/FTIR/DSC analysis. (C) 2017 Elsevier B.V. All rights reserved.