Mukhtiar AHMED1, Fiaz ULLAH SHAH1, Patrik JOHANSSON1
1Lulea University of Technology, Lulea, Sweden, Lulea, Norbotton, Sweden
Five new n-tetrabutylphosphonium (P 4444 ) + cation based ionic liquids (ILs) with oligoether
substituted aromatic carboxylate anions have been synthesized. The nature and position of
the oligoether chain affect both thermal stability (up to 330 ºC), phase behaviour (T g < -55 ºC)
and ion transport. Furthermore, with the aim of application in lithium batteries, electrolytes
were created for two of the ILs by 10 mol% doping using the corresponding Li-salts. This
affects the ion diffusion negatively, from being higher and equal for cations and anions to
lower for all ions and unequal. This is due to stronger ionic interactions and formation of
aggregates, primarily between the Li + ions and the carboxylate group of the anions.
Electrochemically, the electrolytes have electrochemical stability windows up to 3.5 V, giving
some promise for battery application.