Use this URL to cite or link to this record in EThOS: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.750987
Title: Conductivity and nuclear magnetic resonance studies on polymer electrolytes based on poly(ethylene oxide)
Author: Tomlin, Anthony Stephen
Awarding Body: University of St Andrews
Current Institution: University of St Andrews
Date of Award: 1988
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Abstract:
The thesis details studies relating to polymer electrolytes; the solid ionic conductors farmed by the dissolution of salts in suitable high molecular weight polymers. An outline of polymer electrolyte study is presented with respect to current understanding of the phase behaviour, morphology and conductance behaviour of the electrolyte materials. (In particular, those based upon the linear homopolymer poly(ethylene oxide), PEO.) An electrochemical study has been undertaken (298 K) involving a low molecular weight PEO analogue, PEO(400)e = CH3C02(CH2CH20) CO CH3 (n = 8 - 9 ), containing LiCF3SO3 or LiClO4. The study has shown that at low to medium salt concentrations in polyether media ion - ion interactions are important and are realized as ion association. The conductance vs. concentration behaviour has been modelled according to an equilibrium between single, ion pair and triple ion species where the concentration of simple (single) ions are small and decreasing, and above a total salt concentration of about 0.01 mol kg−1, the majority of the current is carried by triple ion species of the form Li2X- LiX2 (X = CF3SO3 , CIO4). Equilibrium constant data were obtained for single and triple ion formation (from neutral ion pairs). Determination of triple ion formation constants vs. temperature has shown that the triple ion formation process for LiCF3SO3 in PEO(400)e is an exothermic process, negative, whereas for LiClO4 AH = 0 kJinal−1. Using nuclear magnetic resonance (nmr), diffusion coefficients have been obtained for the oligomer chain in PEO(400)e and PEO(400)e.LiCF3SO3 solutions. The chain diffusion coefficients have been shown to give good agreement with those for salt diffusion, determined from conductance measurements via the Nernst - Einstein relation. An in - depth nmr investigation of the PEO.LICF3SO3 system (high molecular weight PEO) has shown that there is partition of lithium environments, probably within the salt rich crystalline phase (EQ/Li - 3.5/1). Significant numbers of lithium nuclei are not observed with the nmr technique because they occupy environments of law symmetry. This was reinforced by other nmr measurements which suggested cation - anion proximity in the crystalline phase. A mixed salt system has been studied, PEO. LiCF3SO3. Nal, and it has been shown that the mixing of salts gave materials with superior conductivities to the relevant single salt systems (PEO. LiCF3SO3 and PEO.Nal) of the same overall salt content. Nmr has shown that the mixed salt effect was due to a larger amorphous (conducting) polymer phase and more potential charge carriers for the mixed salt in comparison to the single salt materials. A marked effect upon lithium motion was observed for PEO.LiCF3SO3 Nal system in comparison to PEO.LiCF3SO3 and it has been proposed that this was due to the observed lithium species becoming mobile at notably lower temperatures for the mixed salt system.
Supervisor: MacCallum, James Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.750987  DOI: Not available
Keywords: QD565.P7T7 ; Electrolytes
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