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

Abstract

New methods for the high-throughput characterisation of polymer electrolytes have
been developed. Polymer electrolytes for use in lithium ion batteries have been
prepared in a novel systematic manner that involves parallel preparation and subsequent
high-throughput conductivity measurements of up to 64 individual compositions in a
multi-electrode cell. The method of casting the polymer electrolytes directly onto the
substrate also allows high-throughput characterisation by x-ray diffraction. The
technique was applied specifically to a ternary system of PVdF-HFP, LiTFSI and PC.
By preparing a vast array of samples across the composition range, it was found that the
conductivity reached a maximum value when the weight fraction composition was
0.45/0.45/0.1 of PVdF-HFP/LiTFSI/PC with completely free standing samples. The
trend of increasing conductivity tended towards the maximum liquid conductivity of
LiTFSI/PC.

Due to limitations of this method with highly conductive polymer electrolytes, a
second novel alternative polymer synthesis, preparation and measurement technique
was developed for proton conducting polymers for fuel cell applications. In addition a
second multi-electrode cell was designed and constructed specifically allowing AC
Impedance measurements to be taken whilst allowing the polymer electrolytes to be
subjected to temperature and relative humidity effects. The multi-electrode cell was
calibrated using commercially available Nafion samples before being used with
synthesised samples. PEEK was sulfonated to SPEEK using varying temperatures and
reaction times to obtain many samples with differing DS values. The conductivity of
the samples was measured in situ using an in-plane 4 electrode impedance
measurement, over a range of environmental conditions. It was found that water loss
caused significant conductivity decay under PEMFC conditions for Nafion but not for
SPEEK samples. SPEEK with a DS of 75 % was found to have the maximum SPEEK
equilibration conductivity of 0.177 S cm-1, a value comparable to that of commercial
membranes. By blending this sample with a lower DS SPEEK, high conductivity
values could be maintained at temperatures of 105 °C and 75 % relative humidity with
maintained mechanical integrity. When an inorganic additive (Zr(HPO4)2) was
introduced into the blended samples, the conductivity was enhanced further due to
increased water retention within the phosphate structure.

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Identifiers

ORCID for John Owen: orcid.org/0000-0002-4938-3693

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