Abstract
Thermal treatment conditions of solid polymer polymer electrolyte (SPE) were studied with respect to their impact on the surface morphology, phase composition and chemical composition of an imidazolium ionic-liquid-based SPE, namely PVDF/NMP/[EMIM][TFSI] electrolyte. These investigations were done using scanning electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry as well as X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy. A thoroughly mixed blend of polymer matrix, ionic liquid and solvent was deposited on a ceramic substrate and was kept at a certain temperature for a specific time in order to achieve varying crystallinity. The morphology of all the electrolytes consists of spherulites whose average diameter increases with solvent evaporation rate. Raman mapping shows that these spherulites have a semicrystalline structure and the area between them is an amorphous region. Analysis of FTIR spectra as well as Raman spectroscopy showed that the β-phase becomes dominant over other phases, while DSC technique indicated decrease of crystallinity as the solvent evaporation rate increases. XPS and ToF-SIMS indicated that the chemical composition of the surface of the SPE samples with the highest solvent evaporation rate approaches the composition of the ionic liquid.
Highlights
Solid polymer electrolytes (SPEs) could be and safely prepared as flexible thin films in desirable sizes with good electrochemical stability and good mechanical properties [1,2,3,4,5]
This paper builds on earlier research which described the effect of thermal treatment conditions on AC/DC conductivity and current fluctuations of polyvinylidene fluoride (PVDF)/ionic liquid (IL)-based solid polymer electrolyte [18] as well as on the characterization of PVDF/NMP/[EMIM][TFSI] based amperometric sensors [30,31,32,33]
The solid polymer electrolyte is a mixture of three basic components: (i) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI], Merck, Darmstadt, Germany) as ionic liquid, (ii) poly-(vinylidene fluoride) (PVDF, Lyon, SigmaAldrich, France) as polymer matrix, (iii) N-methyl-pyrrolidone (NMP, VWR, Fontenay-sousBois, France) as a solvent
Summary
Solid polymer electrolytes (SPEs) could be and safely prepared as flexible thin films in desirable sizes with good electrochemical stability and good mechanical properties [1,2,3,4,5]. Several authors have described methods for fabricating electrochemical gas SPE-based sensors on a flexible substrate which are inexpensive and mass produced [8,13,14] These printed gas sensors may show a certain drawbacks in a low selectivity, a low consistency of performance in short-time and long-time periods [13]. Ion transport occurs predominantly in the amorphous region where the segmental motion of polymer chains becomes faster, the co-occurrence of crystalline and amorphous phases in PVDF-based SPEs fundamentally affects the ionic conductivity [17,19,20]. Besides techniques such as blending, addition of additives, etc. This paper builds on earlier research which described the effect of thermal treatment conditions on AC/DC conductivity and current fluctuations of PVDF/IL-based solid polymer electrolyte [18] as well as on the characterization of PVDF/NMP/[EMIM][TFSI] based amperometric sensors [30,31,32,33]
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