New high-throughput methods of investigating polymer electrolytes

Polymer electrolyte films have been prepared by solution casting techniques from precursor solutions of a poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), lithium-bis(trifluoromethane) sulfonimide (LiTFSI), and propylene carbonate (PC). Arrays of graded composition were characterised by electrochemical impedance spectroscopy (EIS), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) using high throughput techniques. Impedance analysis showed the resistance of the films as a function of LiTFSI, PC and polymer content. The ternary plot of conductivity shows an area that combines a solid-like mechanical stability with high conductivity, 1 x 10(-5) S cm(-1) at the composition 0.55/0.15/0.30 wt% PVdF-HFP/LiTFSI/PC, increasing with PC content. In regions with less than a 50 wt% fraction of PVdF-HFP the films were too soft to give meaningful results by this method. The DSC measurements on solvent free, salt-doped polymers show a reduced crystallinity, and high throughput XRD patterns show that non-polar crystalline phases are suppressed by the presence of LiTFSI and PC. (C) 2010 Elsevier B.V. All rights reserved.