High throughput studies of polymer electrolyte for battery and fuel cell applications

New methods for the high-throughput characterisation of polymer electrolytes have<br/>been developed. Polymer electrolytes for use in lithium ion batteries have been<br/>prepared in a novel systematic manner that involves parallel preparation and subsequent<br/>high-throughput conductivity measurements of up to 64 individual compositions in a<br/>multi-electrode cell. The method of casting the polymer electrolytes directly onto the<br/>substrate also allows high-throughput characterisation by x-ray diffraction. The<br/>technique was applied specifically to a ternary system of PVdF-HFP, LiTFSI and PC.<br/>By preparing a vast array of samples across the composition range, it was found that the<br/>conductivity reached a maximum value when the weight fraction composition was<br/>0.45/0.45/0.1 of PVdF-HFP/LiTFSI/PC with completely free standing samples. The<br/>trend of increasing conductivity tended towards the maximum liquid conductivity of<br/>LiTFSI/PC.<br/><br/>Due to limitations of this method with highly conductive polymer electrolytes, a<br/>second novel alternative polymer synthesis, preparation and measurement technique<br/>was developed for proton conducting polymers for fuel cell applications. In addition a<br/>second multi-electrode cell was designed and constructed specifically allowing AC<br/>Impedance measurements to be taken whilst allowing the polymer electrolytes to be<br/>subjected to temperature and relative humidity effects. The multi-electrode cell was<br/>calibrated using commercially available Nafion samples before being used with<br/>synthesised samples. PEEK was sulfonated to SPEEK using varying temperatures and<br/>reaction times to obtain many samples with differing DS values. The conductivity of<br/>the samples was measured in situ using an in-plane 4 electrode impedance<br/>measurement, over a range of environmental conditions. It was found that water loss<br/>caused significant conductivity decay under PEMFC conditions for Nafion but not for<br/>SPEEK samples. SPEEK with a DS of 75 % was found to have the maximum SPEEK<br/>equilibration conductivity of 0.177 S cm-1, a value comparable to that of commercial<br/>membranes. By blending this sample with a lower DS SPEEK, high conductivity<br/>values could be maintained at temperatures of 105 °C and 75 % relative humidity with<br/>maintained mechanical integrity. When an inorganic additive (Zr(HPO4)2) was<br/>introduced into the blended samples, the conductivity was enhanced further due to<br/>increased water retention within the phosphate structure.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2009

Author dc:creator

• Alcock, Hannah

Advisor dc:contributor.advisor

• Owen, John