Characterisation and modelling of the transport properties in lithium battery polymer electrolytes

• The ionic transport properties of solid polymer electrolytes can limit the performance of lithium batteries and are difficult to characterise. Few characterisation methods are available and the reported results show large discrepancies and the methods do not take variations of the properties with salt concentration into account although such are typical for polymer electrolytes. In this study, numerical macroscopic modelling, using the concentrated solution theory, was employed to determine the transport properties and thermodynamic activity factor, allowing concentration-dependent parameters. A copolymer of ethylene oxide and propylene oxide with 0.11 - 2 M LiTFSI was characterised at 25 degreesC using chronopotentiometry and concentration cell experiments. The determined ionic conductivity, kappa, apparent salt diffusion coefficient, D-s and cationic transport number, t(+)(0), were in line with previous results and kappa was also verified using electrochemical impedance spectroscopy. t(+)(0) values below 0.25 were measured, showing a decrease with increasing salt concentration. It was found that it was important to take into account the concentration dependence of the transport properties as well as the ionic interaction and the activity factor of the salt. The study resulted in a transport model well suited for the system that can easily be used to simulate the electrolyte behaviour for any current.

Nyckelord

lithium

polymer electrolyte

transport properties

modelling

characterisation

transference number measurements

molecular-weight

potentiostatic polarization

peo-litfsi

conductivity

system

cells

mobility

charge

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