Ionic Conductivity in Crystalline Polymer Electrolytes
The ionic conductivity of a material is an essential property in order to evaluate its ability as an electrolyte in other words its abilityto conduct current. In polymers electrolytes it was longer assumed that amorphous phase was the sole phase involved in the conductivity. However, the article this essay is based on, the authors try toprove that despite this prevailing view, the ionic conductivity in the crystalline structure can be greater than that in the amorphous material above Tg.
The figure below show the conductivity as afunction of temperature for crystalline and amorphous PEO6:LiSbF6 materials and it is evident that crystalline phase shows a higher conductivity than amorphous phase.
Polymer Electrolytes can beformed by dissolving an ionic salt in a solid host polymer. They can be prepared in both the crystalline and amorphous phases [1-4]. The authors of the article in question based their study oncrystalline PEO6: LiSbF6 and PEO6:LiPF6. These were synthesised by dissolving LISbF6 or LiPF6 and Polyethylene oxide (PEO) in acetonitrile. It was important that the Mw in PEO was 1,000 in the synthesis on thecrystalline phase as at high Mw the amorphous phase would coexist. When comparing the crystalline phase to the amorphous phase of the same composition [5-6], the amorphous phase had to have anMw=100,000 (above entanglement limit for PEO of 3,200). A NMR study of polymer used in conductivity comparison, show that at room temperature the PEO6:LiSbF6 materials are respectively amorphous andcrystalline. So it is a good material for conductivity study, but why crystalline phase is a better conductor?
This can be explained by ionic transport method in solids which involves thehopping of ions between adjacent sites. In polymer electrolytes, the conventional view of ionic conductivity involves ions moving in a dynamic environment created by the polymer chain motion of the...
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